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| author |   Ben Hutchings <ben@decadent.org.uk> | 2009-09-10 02:53:50 +0100 |
|---|---|---|
| committer |   H. Peter Anvin <hpa@zytor.com> | 2009-09-10 16:50:19 -0700 |
| commit | 5367b6887e7d8c870a5da7d9b8c6e9c207684e43 (patch) | |
| tree | eab362078a7964850b00f8d781aa9c9f5ff01df7 | |
| parent | x86, msr: change msr-reg.o to obj-y, and export its symbols (diff) | |
| download | linux-dev-5367b6887e7d8c870a5da7d9b8c6e9c207684e43.tar.xz linux-dev-5367b6887e7d8c870a5da7d9b8c6e9c207684e43.zip | |
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>
| -rw-r--r-- | arch/x86/include/asm/processor.h | 16 | ||||
| -rw-r--r-- | arch/x86/kernel/alternative.c | 2 |
2 files changed, 14 insertions, 4 deletions
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index c7768269b1cf..2db56c57a281 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -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, diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index f57658702571..b8ebd0b689b1 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -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; |