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x86: Fix code patching for paravirt-alternatives on 486 

As reported in <http://bugs.debian.org/511703> and
<http://bugs.debian.org/515982>, kernels with paravirt-alternatives
enabled crash in text_poke_early() on at least some 486-class
processors.

The problem is that text_poke_early() itself uses inline functions
affected by paravirt-alternatives and so will modify instructions that
have already been prefetched.  Pentium and later processors will
invalidate the prefetched instructions in this case, but 486-class
processors do not.

Change sync_core() to limit prefetching on 486-class (and 386-class)
processors, and move the call to sync_core() above the call to the
modifiable local_irq_restore().

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
LKML-Reference: <1252547631.3423.134.camel@localhost>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Ben Hutchings 2009-09-10 02:53:50 +01:00 committed by H. Peter Anvin
parent b19ae39998
commit 5367b6887e
2 changed files with 14 additions and 4 deletions
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16
arch/x86/include/asm/processor.h
View File

@ -703,13 +703,23 @@ static inline void cpu_relax(void)
rep_nop();
}
/* Stop speculative execution: */
/* Stop speculative execution and prefetching of modified code. */
static inline void sync_core(void)
{
int tmp;
asm volatile("cpuid" : "=a" (tmp) : "0" (1)
: "ebx", "ecx", "edx", "memory");
#if defined(CONFIG_M386) || defined(CONFIG_M486)
if (boot_cpu_data.x86 < 5)
/* There is no speculative execution.
* jmp is a barrier to prefetching. */
asm volatile("jmp 1f\n1:\n" ::: "memory");
else
#endif
/* cpuid is a barrier to speculative execution.
* Prefetched instructions are automatically
* invalidated when modified. */
asm volatile("cpuid" : "=a" (tmp) : "0" (1)
: "ebx", "ecx", "edx", "memory");
}
static inline void __monitor(const void *eax, unsigned long ecx,

2
arch/x86/kernel/alternative.c
View File

@ -490,8 +490,8 @@ void *text_poke_early(void *addr, const void *opcode, size_t len)
unsigned long flags;
local_irq_save(flags);
memcpy(addr, opcode, len);
local_irq_restore(flags);
sync_core();
local_irq_restore(flags);
/* Could also do a CLFLUSH here to speed up CPU recovery; but
that causes hangs on some VIA CPUs. */
return addr;