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Merge patch series "RISC-V: Fixes for riscv_has_extension[un]likely()'s alternative dependency"

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Conor Dooley <conor.dooley@microchip.com> says:

Here's my attempt at fixing both the use of an FPU on XIP kernels and
the issue that Jason ran into where CONFIG_FPU, which needs the
alternatives frame work for has_fpu() checks, could be enabled without
the alternatives actually being present.

For the former, a "slow" fallback that does not use alternatives is
added to riscv_has_extension_[un]likely() that can be used with XIP.
Obviously, we want to make use of Jisheng's alternatives based approach
where possible, so any users of riscv_has_extension_[un]likely() will
want to make sure that they select RISCV_ALTERNATIVE.
If they don't however, they'll hit the fallback path which (should,
sparing a silly mistake from me!) behave in the same way, thus
succeeding silently. Sounds like a

To prevent "depends on !XIP_KERNEL; select RISCV_ALTERNATIVE" spreading
like the plague through the various places that want to check for the
presence of extensions, and sidestep the potential silent "success"
mentioned above, all users RISCV_ALTERNATIVE are converted from selects
to dependencies, with the option being selected for all !XIP_KERNEL
builds.

I know that the VDSO was a key place that Jisheng wanted to use the new
helper rather than static branches, and I think the fallback path
should not cause issues there.

See the thread at [1] for the prior discussion.

1 - https://lore.kernel.org/linux-riscv/20230128172856.3814-1-jszhang@kernel.org/T/#m21390d570997145d31dd8bb95002fd61f99c6573

[Palmer: these were also merged into fixes, but there's a cleanup that
depends on the merge so I'm taking it into for-next as well.]

* b4-shazam-merge:
  RISC-V: always select RISCV_ALTERNATIVE for non-xip kernels
  RISC-V: add non-alternative fallback for riscv_has_extension_[un]likely()

Link: https://lore.kernel.org/r/20230324100538.3514663-1-conor.dooley@microchip.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

* commit '1ee7fc3f4d0a93831a20d5566f203d5ad6d44de8':
  RISC-V: always select RISCV_ALTERNATIVE for non-xip kernels
  RISC-V: add non-alternative fallback for riscv_has_extension_[un]likely()
This commit is contained in:
Palmer Dabbelt 2023-03-29 11:56:08 -07:00
commit be693ef2a4
No known key found for this signature in database
GPG Key ID: 2E1319F35FBB1889
3 changed files with 38 additions and 30 deletions
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12
arch/riscv/Kconfig
View File

@ -127,6 +127,7 @@ config RISCV
select OF_IRQ
select PCI_DOMAINS_GENERIC if PCI
select PCI_MSI if PCI
select RISCV_ALTERNATIVE if !XIP_KERNEL
select RISCV_INTC
select RISCV_TIMER if RISCV_SBI
select SIFIVE_PLIC
@ -420,9 +421,8 @@ config RISCV_ISA_SVNAPOT
config RISCV_ISA_SVPBMT
bool "SVPBMT extension support"
depends on 64BIT && MMU
depends on !XIP_KERNEL
depends on RISCV_ALTERNATIVE
default y
select RISCV_ALTERNATIVE
help
Adds support to dynamically detect the presence of the SVPBMT
ISA-extension (Supervisor-mode: page-based memory types) and
@ -447,8 +447,8 @@ config TOOLCHAIN_HAS_ZBB
config RISCV_ISA_ZBB
bool "Zbb extension support for bit manipulation instructions"
depends on TOOLCHAIN_HAS_ZBB
depends on !XIP_KERNEL && MMU
select RISCV_ALTERNATIVE
depends on MMU
depends on RISCV_ALTERNATIVE
default y
help
Adds support to dynamically detect the presence of the ZBB
@ -462,9 +462,9 @@ config RISCV_ISA_ZBB
config RISCV_ISA_ZICBOM
bool "Zicbom extension support for non-coherent DMA operation"
depends on !XIP_KERNEL && MMU
depends on MMU
depends on RISCV_ALTERNATIVE
default y
select RISCV_ALTERNATIVE
select RISCV_DMA_NONCOHERENT
help
Adds support to dynamically detect the presence of the ZICBOM

6
arch/riscv/Kconfig.errata
View File

@ -2,8 +2,7 @@ menu "CPU errata selection"
config ERRATA_SIFIVE
bool "SiFive errata"
depends on !XIP_KERNEL
select RISCV_ALTERNATIVE
depends on RISCV_ALTERNATIVE
help
All SiFive errata Kconfig depend on this Kconfig. Disabling
this Kconfig will disable all SiFive errata. Please say "Y"
@ -35,8 +34,7 @@ config ERRATA_SIFIVE_CIP_1200
config ERRATA_THEAD
bool "T-HEAD errata"
depends on !XIP_KERNEL
select RISCV_ALTERNATIVE
depends on RISCV_ALTERNATIVE
help
All T-HEAD errata Kconfig depend on this Kconfig. Disabling
this Kconfig will disable all T-HEAD errata. Please say "Y"

50
arch/riscv/include/asm/hwcap.h
View File

@ -59,18 +59,31 @@ struct riscv_isa_ext_data {
unsigned int isa_ext_id;
};
unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
#define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit);
#define riscv_isa_extension_available(isa_bitmap, ext) \
__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
static __always_inline bool
riscv_has_extension_likely(const unsigned long ext)
{
compiletime_assert(ext < RISCV_ISA_EXT_MAX,
"ext must be < RISCV_ISA_EXT_MAX");
asm_volatile_goto(
ALTERNATIVE("j %l[l_no]", "nop", 0, %[ext], 1)
:
: [ext] "i" (ext)
:
: l_no);
if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
asm_volatile_goto(
ALTERNATIVE("j %l[l_no]", "nop", 0, %[ext], 1)
:
: [ext] "i" (ext)
:
: l_no);
} else {
if (!__riscv_isa_extension_available(NULL, ext))
goto l_no;
}
return true;
l_no:
@ -83,26 +96,23 @@ riscv_has_extension_unlikely(const unsigned long ext)
compiletime_assert(ext < RISCV_ISA_EXT_MAX,
"ext must be < RISCV_ISA_EXT_MAX");
asm_volatile_goto(
ALTERNATIVE("nop", "j %l[l_yes]", 0, %[ext], 1)
:
: [ext] "i" (ext)
:
: l_yes);
if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
asm_volatile_goto(
ALTERNATIVE("nop", "j %l[l_yes]", 0, %[ext], 1)
:
: [ext] "i" (ext)
:
: l_yes);
} else {
if (__riscv_isa_extension_available(NULL, ext))
goto l_yes;
}
return false;
l_yes:
return true;
}
unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
#define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit);
#define riscv_isa_extension_available(isa_bitmap, ext) \
__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
#endif
#endif /* _ASM_RISCV_HWCAP_H */