Re: [Xen-devel] [PATCH] x86: always supply .cpuid() handler to x86_emulate()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 10/11/16 12:30, Jan Beulich wrote:
> --- a/xen/arch/x86/traps.c
> +++ b/xen/arch/x86/traps.c
> @@ -2755,6 +2755,24 @@ static int priv_op_write_msr(unsigned in
>      return X86EMUL_UNHANDLEABLE;
>  }
>  
> +int pv_emul_cpuid(unsigned int *eax, unsigned int *ebx, unsigned int *ecx,
> +                  unsigned int *edx, struct x86_emulate_ctxt *ctxt)
> +{
> +    struct cpu_user_regs regs = *ctxt->regs;

You need a CPUID faulting check here, matching the hvm side of things,
or you will leave a latent bug which gets exposed when switching to
using full x86_emulate() for PV guests.

Would it be wise to add a fail_if(!ops->cpuid) to x86_emulate() to catch
other misuses?

~Andrew

> +
> +    regs._eax = *eax;
> +    regs._ecx = *ecx;
> +
> +    pv_cpuid(&regs);
> +
> +    *eax = regs._eax;
> +    *ebx = regs._ebx;
> +    *ecx = regs._ecx;
> +    *edx = regs._edx;
> +
> +    return X86EMUL_OKAY;
> +}
> +
>  /* Instruction fetch with error handling. */
>  #define insn_fetch(type, base, eip, limit)                                  \
>  ({  unsigned long _rc, _ptr = (base) + (eip);                               \


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