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parisc: Add lws_atomic_xchg and lws_atomic_store syscalls
This patch adds two new LWS routines - lws_atomic_xchg and lws_atomic_store. These are simpler than the CAS routines. Currently, we use the CAS routines for atomic stores. This is inefficient since it requires both winning the spinlock and a successful CAS operation. Change has been tested on c8000 and rp3440. In v2, I moved the code to disble/enable page faults inside the spinlocks. Signed-off-by: John David Anglin <dave.anglin@bell.net> Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
John David Anglin
Helge Deller
parent
d0585d742f
commit
72c3dd8207
@ -90,7 +90,7 @@ ENTRY(linux_gateway_page)
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/* ADDRESS 0xb0 to 0xb8, lws uses two insns for entry */
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/* Light-weight-syscall entry must always be located at 0xb0 */
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/* WARNING: Keep this number updated with table size changes */
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#define __NR_lws_entries (3)
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#define __NR_lws_entries (5)
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lws_entry:
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gate lws_start, %r0 /* increase privilege */
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@ -884,6 +884,395 @@ cas2_lock_start:
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ASM_EXCEPTIONTABLE_ENTRY(20b-linux_gateway_page, 31b-linux_gateway_page)
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#endif
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/***************************************************
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LWS atomic exchange.
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%r26 - Exchange address
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%r25 - Size of the variable (0/1/2/3 for 8/16/32/64 bit)
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%r24 - Address of new value
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%r23 - Address of old value
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%r28 - Return non-zero on failure
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%r21 - Kernel error code
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%r21 returns the following error codes:
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EAGAIN - CAS is busy, ldcw failed, try again.
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EFAULT - Read or write failed.
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If EAGAIN is returned, %r28 indicates the busy reason:
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r28 == 1 - CAS is busy. lock contended.
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r28 == 2 - CAS is busy. ldcw failed.
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r28 == 3 - CAS is busy. page fault.
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Scratch: r20, r1
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****************************************************/
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lws_atomic_xchg:
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#ifdef CONFIG_64BIT
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/* Wide mode user process? */
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bb,<,n %sp, 31, atomic_xchg_begin
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/* Clip the input registers for 32-bit processes. We don't
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need to clip %r23 as we only use it for word operations */
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depdi 0, 31, 32, %r26
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depdi 0, 31, 32, %r25
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depdi 0, 31, 32, %r24
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depdi 0, 31, 32, %r23
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#endif
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atomic_xchg_begin:
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/* Check the validity of the size pointer */
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subi,>>= 3, %r25, %r0
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b,n lws_exit_nosys
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/* Jump to the functions which will load the old and new values into
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registers depending on the their size */
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shlw %r25, 2, %r1
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blr %r1, %r0
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nop
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/* Perform exception checks */
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/* 8-bit exchange */
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1: ldb 0(%r24), %r20
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copy %r23, %r20
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depi_safe 0, 31, 2, %r20
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b atomic_xchg_start
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2: stbys,e %r0, 0(%r20)
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nop
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nop
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nop
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/* 16-bit exchange */
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3: ldh 0(%r24), %r20
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copy %r23, %r20
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depi_safe 0, 31, 2, %r20
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b atomic_xchg_start
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4: stbys,e %r0, 0(%r20)
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nop
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nop
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nop
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/* 32-bit exchange */
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5: ldw 0(%r24), %r20
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b atomic_xchg_start
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6: stbys,e %r0, 0(%r23)
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nop
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nop
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nop
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nop
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nop
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/* 64-bit exchange */
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#ifdef CONFIG_64BIT
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7: ldd 0(%r24), %r20
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8: stdby,e %r0, 0(%r23)
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#else
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7: ldw 0(%r24), %r20
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8: ldw 4(%r24), %r20
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copy %r23, %r20
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depi_safe 0, 31, 2, %r20
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9: stbys,e %r0, 0(%r20)
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10: stbys,e %r0, 4(%r20)
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#endif
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atomic_xchg_start:
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/* Trigger memory reference interruptions without writing to memory */
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copy %r26, %r28
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depi_safe 0, 31, 2, %r28
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11: ldw 0(%r28), %r1
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12: stbys,e %r0, 0(%r28)
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/* Calculate 8-bit hash index from virtual address */
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extru_safe %r26, 27, 8, %r20
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/* Load start of lock table */
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ldil L%lws_lock_start, %r28
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ldo R%lws_lock_start(%r28), %r28
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/* Find lock to use, the hash index is one of 0 to
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255, multiplied by 16 (keep it 16-byte aligned)
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and add to the lock table offset. */
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shlw %r20, 4, %r20
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add %r20, %r28, %r20
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rsm PSW_SM_I, %r0 /* Disable interrupts */
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/* Try to acquire the lock */
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LDCW 0(%sr2,%r20), %r28
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comclr,<> %r0, %r28, %r0
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b,n lws_wouldblock
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/* Disable page faults to prevent sleeping in critical region */
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lws_pagefault_disable %r21,%r28
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/* NOTES:
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This all works because intr_do_signal
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and schedule both check the return iasq
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and see that we are on the kernel page
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so this process is never scheduled off
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or is ever sent any signal of any sort,
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thus it is wholly atomic from userspace's
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perspective
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*/
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/* Jump to the correct function */
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blr %r1, %r0
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/* Set %r28 as non-zero for now */
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ldo 1(%r0),%r28
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/* 8-bit exchange */
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14: ldb 0(%r26), %r1
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15: stb %r1, 0(%r23)
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15: ldb 0(%r24), %r1
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17: stb %r1, 0(%r26)
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b lws_exit_noerror
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copy %r0, %r28
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nop
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nop
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/* 16-bit exchange */
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18: ldh 0(%r26), %r1
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19: sth %r1, 0(%r23)
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20: ldh 0(%r24), %r1
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21: sth %r1, 0(%r26)
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b lws_exit_noerror
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copy %r0, %r28
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nop
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nop
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/* 32-bit exchange */
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22: ldw 0(%r26), %r1
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23: stw %r1, 0(%r23)
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24: ldw 0(%r24), %r1
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25: stw %r1, 0(%r26)
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b lws_exit_noerror
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copy %r0, %r28
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nop
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nop
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/* 64-bit exchange */
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#ifdef CONFIG_64BIT
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26: ldd 0(%r26), %r1
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27: std %r1, 0(%r23)
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28: ldd 0(%r24), %r1
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29: std %r1, 0(%r26)
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#else
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26: flddx 0(%r26), %fr4
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27: fstdx %fr4, 0(%r23)
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28: flddx 0(%r24), %fr4
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29: fstdx %fr4, 0(%r26)
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#endif
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b lws_exit_noerror
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copy %r0, %r28
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/* A fault occurred on load or stbys,e store */
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30: b,n lws_fault
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ASM_EXCEPTIONTABLE_ENTRY(1b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(2b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(3b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(4b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(5b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(6b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(7b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(8b-linux_gateway_page, 30b-linux_gateway_page)
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#ifndef CONFIG_64BIT
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ASM_EXCEPTIONTABLE_ENTRY(9b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(10b-linux_gateway_page, 30b-linux_gateway_page)
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#endif
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ASM_EXCEPTIONTABLE_ENTRY(11b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(12b-linux_gateway_page, 30b-linux_gateway_page)
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/* A page fault occurred in critical region */
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31: b,n lws_pagefault
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ASM_EXCEPTIONTABLE_ENTRY(14b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(15b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(16b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(17b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(18b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(19b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(20b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(21b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(22b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(23b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(24b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(25b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(26b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(27b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(28b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(29b-linux_gateway_page, 31b-linux_gateway_page)
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/***************************************************
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LWS atomic store.
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%r26 - Address to store
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%r25 - Size of the variable (0/1/2/3 for 8/16/32/64 bit)
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%r24 - Address of value to store
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%r28 - Return non-zero on failure
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%r21 - Kernel error code
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%r21 returns the following error codes:
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EAGAIN - CAS is busy, ldcw failed, try again.
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EFAULT - Read or write failed.
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If EAGAIN is returned, %r28 indicates the busy reason:
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r28 == 1 - CAS is busy. lock contended.
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r28 == 2 - CAS is busy. ldcw failed.
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r28 == 3 - CAS is busy. page fault.
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Scratch: r20, r1
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****************************************************/
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lws_atomic_store:
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#ifdef CONFIG_64BIT
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/* Wide mode user process? */
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bb,<,n %sp, 31, atomic_store_begin
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/* Clip the input registers for 32-bit processes. We don't
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need to clip %r23 as we only use it for word operations */
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depdi 0, 31, 32, %r26
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depdi 0, 31, 32, %r25
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depdi 0, 31, 32, %r24
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#endif
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atomic_store_begin:
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/* Check the validity of the size pointer */
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subi,>>= 3, %r25, %r0
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b,n lws_exit_nosys
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shlw %r25, 1, %r1
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blr %r1, %r0
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nop
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/* Perform exception checks */
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/* 8-bit store */
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1: ldb 0(%r24), %r20
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b,n atomic_store_start
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nop
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nop
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/* 16-bit store */
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2: ldh 0(%r24), %r20
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b,n atomic_store_start
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nop
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nop
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/* 32-bit store */
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3: ldw 0(%r24), %r20
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b,n atomic_store_start
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nop
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nop
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/* 64-bit store */
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#ifdef CONFIG_64BIT
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4: ldd 0(%r24), %r20
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#else
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4: ldw 0(%r24), %r20
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5: ldw 4(%r24), %r20
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#endif
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atomic_store_start:
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/* Trigger memory reference interruptions without writing to memory */
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copy %r26, %r28
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depi_safe 0, 31, 2, %r28
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6: ldw 0(%r28), %r1
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7: stbys,e %r0, 0(%r28)
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/* Calculate 8-bit hash index from virtual address */
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extru_safe %r26, 27, 8, %r20
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/* Load start of lock table */
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ldil L%lws_lock_start, %r28
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ldo R%lws_lock_start(%r28), %r28
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/* Find lock to use, the hash index is one of 0 to
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255, multiplied by 16 (keep it 16-byte aligned)
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and add to the lock table offset. */
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shlw %r20, 4, %r20
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add %r20, %r28, %r20
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rsm PSW_SM_I, %r0 /* Disable interrupts */
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/* Try to acquire the lock */
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LDCW 0(%sr2,%r20), %r28
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comclr,<> %r0, %r28, %r0
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b,n lws_wouldblock
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/* Disable page faults to prevent sleeping in critical region */
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lws_pagefault_disable %r21,%r28
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/* NOTES:
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This all works because intr_do_signal
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and schedule both check the return iasq
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and see that we are on the kernel page
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so this process is never scheduled off
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or is ever sent any signal of any sort,
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thus it is wholly atomic from userspace's
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perspective
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*/
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/* Jump to the correct function */
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blr %r1, %r0
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/* Set %r28 as non-zero for now */
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ldo 1(%r0),%r28
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/* 8-bit store */
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9: ldb 0(%r24), %r1
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10: stb %r1, 0(%r26)
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b lws_exit_noerror
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copy %r0, %r28
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/* 16-bit store */
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11: ldh 0(%r24), %r1
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12: sth %r1, 0(%r26)
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b lws_exit_noerror
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copy %r0, %r28
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/* 32-bit store */
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13: ldw 0(%r24), %r1
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14: stw %r1, 0(%r26)
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b lws_exit_noerror
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copy %r0, %r28
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/* 64-bit store */
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#ifdef CONFIG_64BIT
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15: ldd 0(%r24), %r1
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16: std %r1, 0(%r26)
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#else
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15: flddx 0(%r24), %fr4
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16: fstdx %fr4, 0(%r26)
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#endif
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b lws_exit_noerror
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copy %r0, %r28
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/* A fault occurred on load or stbys,e store */
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30: b,n lws_fault
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ASM_EXCEPTIONTABLE_ENTRY(1b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(2b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(3b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(4b-linux_gateway_page, 30b-linux_gateway_page)
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#ifndef CONFIG_64BIT
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ASM_EXCEPTIONTABLE_ENTRY(5b-linux_gateway_page, 30b-linux_gateway_page)
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#endif
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ASM_EXCEPTIONTABLE_ENTRY(6b-linux_gateway_page, 30b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(7b-linux_gateway_page, 30b-linux_gateway_page)
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/* A page fault occurred in critical region */
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31: b,n lws_pagefault
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ASM_EXCEPTIONTABLE_ENTRY(9b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(10b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(11b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(12b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(13b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(14b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(15b-linux_gateway_page, 31b-linux_gateway_page)
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ASM_EXCEPTIONTABLE_ENTRY(16b-linux_gateway_page, 31b-linux_gateway_page)
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/* Make sure nothing else is placed on this page */
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.align PAGE_SIZE
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END(linux_gateway_page)
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@ -903,6 +1292,8 @@ ENTRY(lws_table)
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LWS_ENTRY(compare_and_swap32) /* 0 - ELF32 Atomic 32bit CAS */
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LWS_ENTRY(compare_and_swap64) /* 1 - ELF64 Atomic 32bit CAS */
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LWS_ENTRY(compare_and_swap_2) /* 2 - Atomic 64bit CAS */
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LWS_ENTRY(atomic_xchg) /* 3 - Atomic Exchange */
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LWS_ENTRY(atomic_store) /* 4 - Atomic Store */
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END(lws_table)
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/* End of lws table */
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