Messages in this thread | | | Date | Sat, 12 Mar 2016 16:36:15 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v3 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops |
| |
* Andy Lutomirski <luto@kernel.org> wrote:
> This demotes an OOPS and likely panic due to a failed non-"safe" MSR > access to a WARN 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 <luto@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..f310714e6e6d 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(1, "unsafe MSR access error: RDMSR from 0x%x", > + (unsigned int)regs->cx);
Btw., instead of the safe/unsafe naming (which has an emotional and security secondary attribute), shouldn't we move this over to a _check() (or _checking()) naming instead that we do in other places in the kernel?
I.e.:
rdmsr(msr, l, h);
and:
if (rdmsr_check(msr, l, h)) { ... }
and then we could name the helpers as _check() and _nocheck() - which is neutral naming.
Thanks,
Ingo
| |