linux-kernel - Re: [PATCH v7 10/26] KVM: x86: Refine xsave-managed guest register/MSR reset handling

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Date:   Thu, 30 Nov 2023 19:36:49 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, seanjc@...gle.com,
        pbonzini@...hat.com, dave.hansen@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, chao.gao@...el.com,
        rick.p.edgecombe@...el.com, john.allen@....com
Subject: Re: [PATCH v7 10/26] KVM: x86: Refine xsave-managed guest
 register/MSR reset handling

On Fri, 2023-11-24 at 00:53 -0500, Yang Weijiang wrote:
> Tweak the code a bit to facilitate resetting more xstate components in
> the future, e.g., adding CET's xstate-managed MSRs.
> 
> No functional change intended.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/kvm/x86.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b9c2c0cd4cf5..16b4f2dd138a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12132,6 +12132,11 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>  		static_branch_dec(&kvm_has_noapic_vcpu);
>  }
>  
> +static inline bool is_xstate_reset_needed(void)
> +{
> +	return kvm_cpu_cap_has(X86_FEATURE_MPX);
> +}
> +
>  void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  {
>  	struct kvm_cpuid_entry2 *cpuid_0x1;
> @@ -12189,7 +12194,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  	kvm_async_pf_hash_reset(vcpu);
>  	vcpu->arch.apf.halted = false;
>  
> -	if (vcpu->arch.guest_fpu.fpstate && kvm_mpx_supported()) {
> +	if (vcpu->arch.guest_fpu.fpstate && is_xstate_reset_needed()) {
>  		struct fpstate *fpstate = vcpu->arch.guest_fpu.fpstate;
>  
>  		/*
> @@ -12199,8 +12204,12 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  		if (init_event)
>  			kvm_put_guest_fpu(vcpu);
>  
> -		fpstate_clear_xstate_component(fpstate, XFEATURE_BNDREGS);
> -		fpstate_clear_xstate_component(fpstate, XFEATURE_BNDCSR);
> +		if (kvm_cpu_cap_has(X86_FEATURE_MPX)) {
> +			fpstate_clear_xstate_component(fpstate,
> +						       XFEATURE_BNDREGS);
> +			fpstate_clear_xstate_component(fpstate,
> +						       XFEATURE_BNDCSR);
> +		}
>  
>  		if (init_event)
>  			kvm_load_guest_fpu(vcpu);

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky