x86, trampoline: Common infrastructure for low memory trampolines

Common infrastructure for low memory trampolines.  This code installs
the trampolines permanently in low memory very early.  It also permits
multiple pieces of code to be used for this purpose.

This code also introduces a standard infrastructure for computing
symbol addresses in the trampoline code.

The only change to the actual SMP trampolines themselves is that the
64-bit trampoline has been made reusable -- the previous version would
overwrite the code with a status variable; this moves the status
variable to a separate location.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <4D5DFBE4.7090104@intel.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Matthieu Castet <castet.matthieu@free.fr>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>

arch/x86/Kconfig

@@ -217,10 +217,6 @@ config X86_HT
 	def_bool y
 	depends on SMP
 
-config X86_TRAMPOLINE
-	def_bool y
-	depends on SMP || (64BIT && ACPI_SLEEP)
-
 config X86_32_LAZY_GS
 	def_bool y
 	depends on X86_32 && !CC_STACKPROTECTOR

arch/x86/kernel/Makefile

@@ -47,7 +47,7 @@ obj-y			+= tsc.o io_delay.o rtc.o
 obj-y			+= pci-iommu_table.o
 obj-y			+= resource.o
 
-obj-$(CONFIG_X86_TRAMPOLINE)	+= trampoline.o
+obj-y				+= trampoline.o trampoline_$(BITS).o
 obj-y				+= process.o
 obj-y				+= i387.o xsave.o
 obj-y				+= ptrace.o
@@ -69,7 +69,6 @@ obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_SMP)		+= smpboot.o tsc_sync.o
 obj-$(CONFIG_SMP)		+= setup_percpu.o
 obj-$(CONFIG_X86_64_SMP)	+= tsc_sync.o
-obj-$(CONFIG_X86_TRAMPOLINE)	+= trampoline_$(BITS).o
 obj-$(CONFIG_X86_MPPARSE)	+= mpparse.o
 obj-y				+= apic/
 obj-$(CONFIG_X86_REBOOTFIXUPS)	+= reboot_fixups_32.o

arch/x86/kernel/head32.c

@@ -34,15 +34,6 @@ void __init i386_start_kernel(void)
 {
 	memblock_init();
 
-#ifdef CONFIG_X86_TRAMPOLINE
-	/*
-	 * But first pinch a few for the stack/trampoline stuff
-	 * FIXME: Don't need the extra page at 4K, but need to fix
-	 * trampoline before removing it. (see the GDT stuff)
-	 */
-	memblock_x86_reserve_range(PAGE_SIZE, PAGE_SIZE + PAGE_SIZE, "EX TRAMPOLINE");
-#endif
-
 	memblock_x86_reserve_range(__pa_symbol(&_text), __pa_symbol(&__bss_stop), "TEXT DATA BSS");
 
 #ifdef CONFIG_BLK_DEV_INITRD

arch/x86/kernel/head_64.S

@@ -136,10 +136,9 @@ ident_complete:
 	/* Fixup phys_base */
 	addq	%rbp, phys_base(%rip)
 
-#ifdef CONFIG_X86_TRAMPOLINE
+	/* Fixup trampoline */
 	addq	%rbp, trampoline_level4_pgt + 0(%rip)
 	addq	%rbp, trampoline_level4_pgt + (511*8)(%rip)
-#endif
 
 	/* Due to ENTRY(), sometimes the empty space gets filled with
 	 * zeros. Better take a jmp than relying on empty space being

arch/x86/kernel/setup.c

@@ -935,7 +935,7 @@ void __init setup_arch(char **cmdline_p)
 	printk(KERN_DEBUG "initial memory mapped : 0 - %08lx\n",
 			max_pfn_mapped<<PAGE_SHIFT);
 
-	reserve_trampoline_memory();
+	setup_trampolines();
 
 #ifdef CONFIG_ACPI_SLEEP
 	/*

arch/x86/kernel/smpboot.c

@@ -788,7 +788,7 @@ do_rest:
 	stack_start  = c_idle.idle->thread.sp;
 
 	/* start_ip had better be page-aligned! */
-	start_ip = setup_trampoline();
+	start_ip = trampoline_address();
 
 	/* So we see what's up */
 	announce_cpu(cpu, apicid);
@@ -798,6 +798,8 @@ do_rest:
 	 * the targeted processor.
 	 */
 
+	printk(KERN_DEBUG "smpboot cpu %d: start_ip = %lx\n", cpu, start_ip);
+
 	atomic_set(&init_deasserted, 0);
 
 	if (get_uv_system_type() != UV_NON_UNIQUE_APIC) {
@@ -851,8 +853,8 @@ do_rest:
 			pr_debug("CPU%d: has booted.\n", cpu);
 		else {
 			boot_error = 1;
-			if (*((volatile unsigned char *)trampoline_base)
+			if (*(volatile u32 *)TRAMPOLINE_SYM(trampoline_status)
-					== 0xA5)
+			    == 0xA5A5A5A5)
 				/* trampoline started but...? */
 				pr_err("CPU%d: Stuck ??\n", cpu);
 			else
@@ -878,7 +880,7 @@ do_rest:
 	}
 
 	/* mark "stuck" area as not stuck */
-	*((volatile unsigned long *)trampoline_base) = 0;
+	*(volatile u32 *)TRAMPOLINE_SYM(trampoline_status) = 0;
 
 	if (get_uv_system_type() != UV_NON_UNIQUE_APIC) {
 		/*

arch/x86/kernel/trampoline.c

@@ -2,39 +2,41 @@
 #include <linux/memblock.h>
 
 #include <asm/trampoline.h>
+#include <asm/cacheflush.h>
 #include <asm/pgtable.h>
 
-#if defined(CONFIG_X86_64) && defined(CONFIG_ACPI_SLEEP)
+unsigned char *x86_trampoline_base;
-#define __trampinit
-#define __trampinitdata
-#else
-#define __trampinit __cpuinit
-#define __trampinitdata __cpuinitdata
-#endif
 
-/* ready for x86_64 and x86 */
+void __init setup_trampolines(void)
-unsigned char *__trampinitdata trampoline_base;
-
-void __init reserve_trampoline_memory(void)
 {
 	phys_addr_t mem;
+	size_t size = PAGE_ALIGN(x86_trampoline_end - x86_trampoline_start);
 
 	/* Has to be in very low memory so we can execute real-mode AP code. */
-	mem = memblock_find_in_range(0, 1<<20, TRAMPOLINE_SIZE, PAGE_SIZE);
+	mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE);
 	if (mem == MEMBLOCK_ERROR)
 		panic("Cannot allocate trampoline\n");
 
-	trampoline_base = __va(mem);
+	x86_trampoline_base = __va(mem);
-	memblock_x86_reserve_range(mem, mem + TRAMPOLINE_SIZE, "TRAMPOLINE");
+	memblock_x86_reserve_range(mem, mem + size, "TRAMPOLINE");
+
+	printk(KERN_DEBUG "Base memory trampoline at [%p] %llx size %zu\n",
+	       x86_trampoline_base, (unsigned long long)mem, size);
+
+	memcpy(x86_trampoline_base, x86_trampoline_start, size);
 }
 
 /*
- * Currently trivial. Write the real->protected mode
+ * setup_trampolines() gets called very early, to guarantee the
- * bootstrap into the page concerned. The caller
+ * availability of low memory.  This is before the proper kernel page
- * has made sure it's suitably aligned.
+ * tables are set up, so we cannot set page permissions in that
+ * function.  Thus, we use an arch_initcall instead.
  */
-unsigned long __trampinit setup_trampoline(void)
+static int __init configure_trampolines(void)
 {
-	memcpy(trampoline_base, trampoline_data, TRAMPOLINE_SIZE);
+	size_t size = PAGE_ALIGN(x86_trampoline_end - x86_trampoline_start);
-	return virt_to_phys(trampoline_base);
+
+	set_memory_x((unsigned long)x86_trampoline_base, size >> PAGE_SHIFT);
+	return 0;
 }
+arch_initcall(configure_trampolines);

arch/x86/kernel/trampoline_32.S

@@ -32,9 +32,11 @@
 #include <asm/segment.h>
 #include <asm/page_types.h>
 
-/* We can free up trampoline after bootup if cpu hotplug is not supported. */
+#ifdef CONFIG_SMP
-__CPUINITRODATA
+
-.code16
+	.section ".x86_trampoline","a"
+	.balign PAGE_SIZE
+	.code16
 
 ENTRY(trampoline_data)
 r_base = .
@@ -44,7 +46,7 @@ r_base = .
 
 	cli			# We should be safe anyway
 
-	movl	$0xA5A5A5A5, trampoline_data - r_base
+	movl	$0xA5A5A5A5, trampoline_status - r_base
 				# write marker for master knows we're running
 
 	/* GDT tables in non default location kernel can be beyond 16MB and
@@ -72,5 +74,10 @@ boot_idt_descr:
 	.word	0				# idt limit = 0
 	.long	0				# idt base = 0L
 
+ENTRY(trampoline_status)
+	.long	0
+
 .globl trampoline_end
 trampoline_end:
+
+#endif /* CONFIG_SMP */

arch/x86/kernel/trampoline_64.S

@@ -32,13 +32,9 @@
 #include <asm/segment.h>
 #include <asm/processor-flags.h>
 
-#ifdef CONFIG_ACPI_SLEEP
+	.section ".x86_trampoline","a"
-.section .rodata, "a", @progbits
+	.balign PAGE_SIZE
-#else
+	.code16
-/* We can free up the trampoline after bootup if cpu hotplug is not supported. */
-__CPUINITRODATA
-#endif
-.code16
 
 ENTRY(trampoline_data)
 r_base = .
@@ -50,7 +46,7 @@ r_base = .
 	mov	%ax, %ss
 
 
-	movl	$0xA5A5A5A5, trampoline_data - r_base
+	movl	$0xA5A5A5A5, trampoline_status - r_base
 				# write marker for master knows we're running
 
 					# Setup stack
@@ -64,10 +60,13 @@ r_base = .
 	movzx	%ax, %esi		# Find the 32bit trampoline location
 	shll	$4, %esi
 
-					# Fixup the vectors
+					# Fixup the absolute vectors
-	addl	%esi, startup_32_vector - r_base
+	leal	(startup_32 - r_base)(%esi), %eax
-	addl	%esi, startup_64_vector - r_base
+	movl	%eax, startup_32_vector - r_base
-	addl	%esi, tgdt + 2 - r_base	# Fixup the gdt pointer
+	leal	(startup_64 - r_base)(%esi), %eax
+	movl	%eax, startup_64_vector - r_base
+	leal	(tgdt - r_base)(%esi), %eax
+	movl	%eax, (tgdt + 2 - r_base)
 
 	/*
 	 * GDT tables in non default location kernel can be beyond 16MB and
@@ -129,6 +128,7 @@ no_longmode:
 	jmp no_longmode
 #include "verify_cpu.S"
 
+	.balign 4
 	# Careful these need to be in the same 64K segment as the above;
 tidt:
 	.word	0			# idt limit = 0
@@ -156,6 +156,12 @@ startup_64_vector:
 	.long	startup_64 - r_base
 	.word	__KERNEL_CS, 0
 
+	.balign 4
+fixup_base:
+	.long	0
+ENTRY(trampoline_status)
+	.long	0
+
 trampoline_stack:
 	.org 0x1000
 trampoline_stack_end:

arch/x86/kernel/vmlinux.lds.S

@@ -240,6 +240,18 @@ SECTIONS
 
 	INIT_DATA_SECTION(16)
 
+	/*
+	 * Code and data for a variety of lowlevel trampolines, to be
+	 * copied into base memory (< 1 MiB) during initialization.
+	 * Since it is copied early, the main copy can be discarded
+	 * afterwards.
+	 */
+	 .x86_trampoline : AT(ADDR(.x86_trampoline) - LOAD_OFFSET) {
+		x86_trampoline_start = .;
+		*(.x86_trampoline)
+		x86_trampoline_end = .;
+	}
+
 	.x86_cpu_dev.init : AT(ADDR(.x86_cpu_dev.init) - LOAD_OFFSET) {
 		__x86_cpu_dev_start = .;
 		*(.x86_cpu_dev.init)
@@ -291,6 +303,7 @@ SECTIONS
 		*(.iommu_table)
 		__iommu_table_end = .;
 	}
+
 	. = ALIGN(8);
 	/*
 	 * .exit.text is discard at runtime, not link time, to deal with