linux-kernel - Re: [RFC PATCH 03/24] KVM: SVM: Add helpers to set/clear ASID flush in VMCB

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Message-ID: <2b040c2922dae99b42db7cc0bf5cc070607c3464.camel@redhat.com>
Date: Thu, 03 Apr 2025 16:00:35 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>, Sean Christopherson
 <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jim Mattson <jmattson@...gle.com>, 
 Vitaly Kuznetsov <vkuznets@...hat.com>, Rik van Riel <riel@...riel.com>,
 Tom Lendacky <thomas.lendacky@....com>,  x86@...nel.org,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 03/24] KVM: SVM: Add helpers to set/clear ASID flush
 in VMCB

On Wed, 2025-03-26 at 19:35 +0000, Yosry Ahmed wrote:
> Incoming changes will add more code paths that set tlb_ctl to
> TLB_CONTROL_FLUSH_ASID, and will eliminate the use of
> TLB_CONTROL_FLUSH_ALL_ASID except as fallback when FLUSHBYASID is not
> available. Introduce set/clear helpers to set tlb_ctl to
> TLB_CONTROL_FLUSH_ASID or TLB_CONTROL_DO_NOTHING.
> 
> Opportunistically move the TLB_CONTROL_* definitions to
> arch/x86/kvm/svm/svm.h as they are not used outside of arch/x86/kvm/svm/.

Same microscopic nitpick as in previous patch :) 
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@...ux.dev>
> ---
>  arch/x86/include/asm/svm.h |  5 -----
>  arch/x86/kvm/svm/nested.c  |  2 +-
>  arch/x86/kvm/svm/sev.c     |  2 +-
>  arch/x86/kvm/svm/svm.c     |  4 ++--
>  arch/x86/kvm/svm/svm.h     | 15 +++++++++++++++
>  5 files changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 9b7fa99ae9513..a97da63562eb3 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -171,11 +171,6 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
>  };
>  
>  
> -#define TLB_CONTROL_DO_NOTHING 0
> -#define TLB_CONTROL_FLUSH_ALL_ASID 1
> -#define TLB_CONTROL_FLUSH_ASID 3
> -#define TLB_CONTROL_FLUSH_ASID_LOCAL 7
> -
>  #define V_TPR_MASK 0x0f
>  
>  #define V_IRQ_SHIFT 8
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 834b67672d50f..11b02a0340d9e 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -681,7 +681,7 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
>  	/* Done at vmrun: asid.  */
>  
>  	/* Also overwritten later if necessary.  */
> -	vmcb02->control.tlb_ctl = TLB_CONTROL_DO_NOTHING;
> +	vmcb_clr_flush_asid(vmcb02);
>  
>  	/* nested_cr3.  */
>  	if (nested_npt_enabled(svm))
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 0bc708ee27887..d613f81addf1c 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3479,7 +3479,7 @@ int pre_sev_run(struct vcpu_svm *svm, int cpu)
>  		return 0;
>  
>  	sd->sev_vmcbs[asid] = svm->vmcb;
> -	svm->vmcb->control.tlb_ctl = TLB_CONTROL_FLUSH_ASID;
> +	vmcb_set_flush_asid(svm->vmcb);
>  	vmcb_mark_dirty(svm->vmcb, VMCB_ASID);
>  	return 0;
>  }
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 28a6d2c0f250f..0e302ae9a8435 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4006,7 +4006,7 @@ static void svm_flush_tlb_asid(struct kvm_vcpu *vcpu)
>  	 * VM-Exit (via kvm_mmu_reset_context()).
>  	 */
>  	if (static_cpu_has(X86_FEATURE_FLUSHBYASID))
> -		svm->vmcb->control.tlb_ctl = TLB_CONTROL_FLUSH_ASID;
> +		vmcb_set_flush_asid(svm->vmcb);
>  	else
>  		svm->current_vmcb->asid_generation--;
>  }
> @@ -4373,7 +4373,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
>  		svm->nested.nested_run_pending = 0;
>  	}
>  
> -	svm->vmcb->control.tlb_ctl = TLB_CONTROL_DO_NOTHING;
> +	vmcb_clr_flush_asid(svm->vmcb);
>  	vmcb_mark_all_clean(svm->vmcb);
>  
>  	/* if exit due to PF check for async PF */
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index d4490eaed55dd..d2c49cbfbf1ca 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -409,6 +409,21 @@ static inline bool vmcb_is_dirty(struct vmcb *vmcb, int bit)
>          return !test_bit(bit, (unsigned long *)&vmcb->control.clean);
>  }
>  
> +#define TLB_CONTROL_DO_NOTHING 0
> +#define TLB_CONTROL_FLUSH_ALL_ASID 1
> +#define TLB_CONTROL_FLUSH_ASID 3
> +#define TLB_CONTROL_FLUSH_ASID_LOCAL 7
> +
> +static inline void vmcb_set_flush_asid(struct vmcb *vmcb)
> +{
> +	vmcb->control.tlb_ctl = TLB_CONTROL_FLUSH_ASID;
> +}
> +
> +static inline void vmcb_clr_flush_asid(struct vmcb *vmcb)
> +{
> +	vmcb->control.tlb_ctl = TLB_CONTROL_DO_NOTHING;
> +}
> +
>  static __always_inline struct vcpu_svm *to_svm(struct kvm_vcpu *vcpu)
>  {
>  	return container_of(vcpu, struct vcpu_svm, vcpu);


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

Best regards,
	Maxim Levitsky