Re: [Xen-devel] [PATCH v1 4/5] x86/msr: introduce guest_rdmsr()

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Sergey Dyasli [mailto:sergey.dyasli@xxxxxxxxxx]
> Sent: Wednesday, August 30, 2017 6:35 PM
> 
> The new function is responsible for handling RDMSR from both HVM and
> PV
> guests. Currently it handles only 2 MSRs:
> 
>     MSR_INTEL_PLATFORM_INFO
>     MSR_INTEL_MISC_FEATURES_ENABLES
> 
> It has a different behaviour compared to the old MSR handlers: if MSR
> is being handled by guest_rdmsr() then RDMSR will either succeed (if
> a guest is allowed to access it based on its MSR policy) or produce
> a GP fault. A guest will never see a H/W value of some MSR unknown to
> this function.
> 
> guest_rdmsr() unifies and replaces the handling code from
> vmx_msr_read_intercept() and priv_op_read_msr().
> 
> Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with a small comment:

> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -3334,11 +3334,16 @@ int hvm_msr_read_intercept(unsigned int msr,
> uint64_t *msr_content)
>      struct vcpu *v = current;
>      struct domain *d = v->domain;
>      uint64_t *var_range_base, *fixed_range_base;
> -    int ret = X86EMUL_OKAY;
> +    int ret;
> 
>      var_range_base = (uint64_t *)v->arch.hvm_vcpu.mtrr.var_ranges;
>      fixed_range_base = (uint64_t *)v->arch.hvm_vcpu.mtrr.fixed_ranges;
> 
> +    if ( (ret = guest_rdmsr(v, msr, msr_content)) !=
> X86EMUL_UNHANDLEABLE )
> +        return ret;
> +    else
> +        ret = X86EMUL_OKAY;
> +

no need to add 'else' here.

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