[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 3/3] x86/emul: Support CPUID faulting via a speculative MSR read
On 20/02/17 10:59, Jan Beulich wrote: >>>> On 20.02.17 at 11:28, <andrew.cooper3@xxxxxxxxxx> wrote: >> --- a/xen/arch/x86/x86_emulate/x86_emulate.c >> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c >> @@ -5424,10 +5424,25 @@ x86_emulate( >> break; >> >> case X86EMUL_OPC(0x0f, 0xa2): /* cpuid */ >> + msr_val = 0; >> fail_if(ops->cpuid == NULL); >> + >> + /* Speculatively read MSR_INTEL_MISC_FEATURES_ENABLES. */ >> + if ( ops->read_msr && >> + (rc = ops->read_msr(MSR_INTEL_MISC_FEATURES_ENABLES, >> + &msr_val, ctxt)) == X86EMUL_EXCEPTION ) >> + { >> + /* Not implemented. Squash the exception and proceed normally. >> */ >> + x86_emul_reset_event(ctxt); >> + rc = X86EMUL_OKAY; >> + } >> + if ( rc != X86EMUL_OKAY ) >> + goto done; >> + >> + generate_exception_if((msr_val & MSR_MISC_FEATURES_CPUID_FAULTING) >> && >> + !mode_ring0(), EXC_GP, 0); /* Faulting >> active? */ > Could you please move the mode_ring0() check up to bypass the > MSR read in the first place? Ok. > >> --- a/xen/arch/x86/x86_emulate/x86_emulate.h >> +++ b/xen/arch/x86/x86_emulate/x86_emulate.h >> @@ -413,12 +413,7 @@ struct x86_emulate_ops >> int (*wbinvd)( >> struct x86_emulate_ctxt *ctxt); >> >> - /* >> - * cpuid: Emulate CPUID via given set of EAX-EDX inputs/outputs. >> - * >> - * May return X86EMUL_EXCEPTION, which causes the emulator to inject >> - * #GP[0]. Used to implement CPUID faulting. >> - */ >> + /* cpuid: Emulate CPUID via given set of EAX-EDX inputs/outputs. */ >> int (*cpuid)( >> uint32_t leaf, >> uint32_t subleaf, > Are there any ways left for the hook to fail? IOW, should its return > type become void now? In principle, it should return RETRY when putting a cpuid entry into the vmevent ring. At the moment, that logic is wedged into the vmx hook, so emulated cpuid instructions don't generate events, but I am looking to fix this (mis)behaviour in the long run. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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