linux-kernel - Re: [PATCH 3/6] KVM: x86: introduce kvm_register_clear

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Message-ID: <YGtCzhDbnAQVgI+8@google.com>
Date:   Mon, 5 Apr 2021 17:03:10 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 3/6] KVM: x86: introduce kvm_register_clear_available

On Thu, Apr 01, 2021, Maxim Levitsky wrote:
> Small refactoring that will be used in the next patch.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---
>  arch/x86/kvm/kvm_cache_regs.h | 7 +++++++
>  arch/x86/kvm/svm/svm.c        | 6 ++----
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
> index 2e11da2f5621..07d607947805 100644
> --- a/arch/x86/kvm/kvm_cache_regs.h
> +++ b/arch/x86/kvm/kvm_cache_regs.h
> @@ -55,6 +55,13 @@ static inline void kvm_register_mark_available(struct kvm_vcpu *vcpu,
>  	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
>  }
>  
> +static inline void kvm_register_clear_available(struct kvm_vcpu *vcpu,

I don't love the name, because it makes me think too hard about available vs.
dirty.  :-)   If we drop the optimizations, what if we also drop this patch to
avoid bikeshedding the name?

> +					       enum kvm_reg reg)
> +{
> +	__clear_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
> +	__clear_bit(reg, (unsigned long *)&vcpu->arch.regs_dirty);
> +}
> +
>  static inline void kvm_register_mark_dirty(struct kvm_vcpu *vcpu,
>  					   enum kvm_reg reg)
>  {
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 271196400495..2843732299a2 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3880,10 +3880,8 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
>  		vcpu->arch.apf.host_apf_flags =
>  			kvm_read_and_reset_apf_flags();
>  
> -	if (npt_enabled) {
> -		vcpu->arch.regs_avail &= ~(1 << VCPU_EXREG_PDPTR);
> -		vcpu->arch.regs_dirty &= ~(1 << VCPU_EXREG_PDPTR);
> -	}
> +	if (npt_enabled)
> +		kvm_register_clear_available(vcpu, VCPU_EXREG_PDPTR);
>  
>  	/*
>  	 * We need to handle MC intercepts here before the vcpu has a chance to
> -- 
> 2.26.2
>