linux-kernel - Re: [PATCH 10/10] KVM: x86: Suppress userspace access failures on unsupported, "emulated" MSRs

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Message-ID: <672782e6-b143-42d0-9ed6-8c343d02e49d@intel.com>
Date: Fri, 26 Apr 2024 15:43:16 +0800
From: "Yang, Weijiang" <weijiang.yang@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 10/10] KVM: x86: Suppress userspace access failures on
 unsupported, "emulated" MSRs

On 4/26/2024 2:14 AM, Sean Christopherson wrote:
> Extend KVM's suppression of userspace MSR access failures to MSRs that KVM
> reports as emulated, but are ultimately unsupported, e.g. if the VMX MSRs
> are emulated by KVM, but are unsupported given the vCPU model.
>
> Suggested-by: Weijiang Yang<weijiang.yang@...el.com>
> Signed-off-by: Sean Christopherson<seanjc@...gle.com>
> ---
>   arch/x86/kvm/x86.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4c91189342ff..14cfa25ef0e7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -491,7 +491,7 @@ static bool kvm_is_immutable_feature_msr(u32 msr)
>   	return false;
>   }
>   
> -static bool kvm_is_msr_to_save(u32 msr_index)
> +static bool kvm_is_advertised_msr(u32 msr_index)
>   {
>   	unsigned int i;
>   
> @@ -500,6 +500,11 @@ static bool kvm_is_msr_to_save(u32 msr_index)
>   			return true;
>   	}
>   
> +	for (i = 0; i < num_emulated_msrs; i++) {
> +		if (emulated_msrs[i] == msr_index)
> +			return true;
> +	}
> +
>   	return false;
>   }
>   
> @@ -529,11 +534,11 @@ static __always_inline int kvm_do_msr_access(struct kvm_vcpu *vcpu, u32 msr,
>   
>   	/*
>   	 * Userspace is allowed to read MSRs, and write '0' to MSRs, that KVM
> -	 * reports as to-be-saved, even if an MSR isn't fully supported.
> +	 * advertises to userspace, even if an MSR isn't fully supported.
>   	 * Simply check that @data is '0', which covers both the write '0' case
>   	 * and all reads (in which case @data is zeroed on failure; see above).
>   	 */
> -	if (host_initiated && !*data && kvm_is_msr_to_save(msr))
> +	if (host_initiated && !*data && kvm_is_advertised_msr(msr))
>   		return 0;
>   
>   	if (!ignore_msrs) {

Reviewed-by: Weijiang Yang <weijiang.yang@...el.com>