From fbd704374d111bed16a19261176fa30e2379c87c Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sat, 2 Apr 2016 07:01:37 -0700 Subject: x86/msr: Carry on after a non-"safe" MSR access fails 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. To be clear, this type of failure should *not* happen. This patch exists to minimize the chance of nasty undebuggable failures happening when a CONFIG_PARAVIRT=y bug in the non-"safe" MSR helpers gets fixed. Tested-by: Boris Ostrovsky Signed-off-by: Andy Lutomirski Acked-by: Linus Torvalds Cc: Andrew Morton Cc: Arjan van de Ven Cc: Borislav Petkov Cc: KVM list Cc: Paolo Bonzini Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: xen-devel Link: http://lkml.kernel.org/r/26567b216aae70e795938f4b567eace5a0eb90ba.1459605520.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/msr.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'arch/x86/include') diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h index 7a79ee2778b3..25f169c6eb95 100644 --- a/arch/x86/include/asm/msr.h +++ b/arch/x86/include/asm/msr.h @@ -84,7 +84,10 @@ 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); @@ -111,7 +114,10 @@ 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); } -- cgit v1.2.3