linux-kernel - Re: [PATCH v13 05/21] KVM: x86: Load guest FPU state when access XSAVE-managed MSRs

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Message-ID: <ae363ab5-8985-4c4e-910e-969d442cd7ed@zytor.com>
Date: Tue, 26 Aug 2025 21:56:59 -0700
From: Xin Li <xin@...or.com>
To: Chao Gao <chao.gao@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc: bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        john.allen@....com, mingo@...hat.com, minipli@...ecurity.net,
        mlevitsk@...hat.com, pbonzini@...hat.com, rick.p.edgecombe@...el.com,
        seanjc@...gle.com, tglx@...utronix.de, weijiang.yang@...el.com,
        x86@...nel.org
Subject: Re: [PATCH v13 05/21] KVM: x86: Load guest FPU state when access
 XSAVE-managed MSRs

On 8/21/2025 6:30 AM, Chao Gao wrote:
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index eb3088684e8a..d90f1009ac10 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -701,4 +701,28 @@ int ____kvm_emulate_hypercall(struct kvm_vcpu *vcpu, int cpl,
>   
>   int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
>   
> +/*
> + * Lock and/or reload guest FPU and access xstate MSRs. For accesses initiated
> + * by host, guest FPU is loaded in __msr_io(). For accesses initiated by guest,
> + * guest FPU should have been loaded already.
> + */
> +
> +static inline void kvm_get_xstate_msr(struct kvm_vcpu *vcpu,
> +				      struct msr_data *msr_info)
> +{
> +	KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm);
> +	kvm_fpu_get();
> +	rdmsrl(msr_info->index, msr_info->data);

s/rdmsrl/rdmsrq/

> +	kvm_fpu_put();
> +}
> +
> +static inline void kvm_set_xstate_msr(struct kvm_vcpu *vcpu,
> +				      struct msr_data *msr_info)
> +{
> +	KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm);
> +	kvm_fpu_get();
> +	wrmsrl(msr_info->index, msr_info->data);

s/wrmsrl/wrmsrq/


Perhaps it's time to remove rdmsrl() and wrmsrl(), as keeping them around
won't trigger any errors when the old APIs are still being used.

> +	kvm_fpu_put();
> +}
> +
>   #endif