Messages in this thread Patch in this message | | | From | Ben Hutchings <> | Date | Thu, 10 Sep 2009 02:53:50 +0100 | Subject | [PATCH v2] x86: Fix code patching for paravirt-alternatives on 486 |
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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> --- Second try, incorporating the jmp into sync_core().
Also not signed as I know git has trouble with MIME.
Ben.
arch/x86/include/asm/processor.h | 16 +++++++++++++--- 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 c776826..2db56c5 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 4869351..de7353c 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -498,8 +498,8 @@ static void *__init_or_module text_poke_early(void *addr, const void *opcode, 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; -- 1.6.3.3
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