This demotes an OOPS and likely panic due to a failed non-"safe" MSR access to a WARN_ONCE and, for RDMSR, a return value of zero. If panic_on_oops is set, then failed unsafe MSR accesses will still oops and panic.
To be clear, this type of failure should *not* happen. This patch exists to minimize the chance of nasty undebuggable failures due on systems that used to work due to a now-fixed CONFIG_PARAVIRT=y bug. Signed-off-by: Andy Lutomirski <l...@kernel.org> --- arch/x86/include/asm/msr.h | 10 ++++++++-- arch/x86/mm/extable.c | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h index 93fb7c1cffda..1487054a1a70 100644 --- a/arch/x86/include/asm/msr.h +++ b/arch/x86/include/asm/msr.h @@ -92,7 +92,10 @@ static inline unsigned long long native_read_msr(unsigned int msr) { DECLARE_ARGS(val, low, high); - asm volatile("rdmsr" : EAX_EDX_RET(val, low, high) : "c" (msr)); + asm volatile("1: rdmsr\n" + "2:\n" + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_rdmsr_unsafe) + : EAX_EDX_RET(val, low, high) : "c" (msr)); if (msr_tracepoint_active(__tracepoint_read_msr)) do_trace_read_msr(msr, EAX_EDX_VAL(val, low, high), 0); return EAX_EDX_VAL(val, low, high); @@ -119,7 +122,10 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr, static inline void native_write_msr(unsigned int msr, unsigned low, unsigned high) { - asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high) : "memory"); + asm volatile("1: wrmsr\n" + "2:\n" + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wrmsr_unsafe) + : : "c" (msr), "a"(low), "d" (high) : "memory"); if (msr_tracepoint_active(__tracepoint_read_msr)) do_trace_write_msr(msr, ((u64)high << 32 | low), 0); } diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index 9dd7e4b7fcde..9e6749b34524 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -49,6 +49,39 @@ bool ex_handler_ext(const struct exception_table_entry *fixup, } EXPORT_SYMBOL(ex_handler_ext); +bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup, + struct pt_regs *regs, int trapnr) +{ + WARN_ONCE(1, "unchecked MSR access error: RDMSR from 0x%x", + (unsigned int)regs->cx); + + /* If panic_on_oops is set, don't try to recover. */ + if (panic_on_oops) + return false; + + regs->ip = ex_fixup_addr(fixup); + regs->ax = 0; + regs->dx = 0; + return true; +} +EXPORT_SYMBOL(ex_handler_rdmsr_unsafe); + +bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup, + struct pt_regs *regs, int trapnr) +{ + WARN_ONCE(1, "unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x)\n", + (unsigned int)regs->cx, + (unsigned int)regs->dx, (unsigned int)regs->ax); + + /* If panic_on_oops is set, don't try to recover. */ + if (panic_on_oops) + return false; + + regs->ip = ex_fixup_addr(fixup); + return true; +} +EXPORT_SYMBOL(ex_handler_wrmsr_unsafe); + bool ex_has_fault_handler(unsigned long ip) { const struct exception_table_entry *e; -- 2.5.0 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel