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From: Paolo Bonzini <pbonzini@redhat.com>
To: Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc: Wanpeng Li <wanpengli@tencent.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Joerg Roedel <joro@8bytes.org>, Borislav Petkov <bp@alien8.de>,
	Sean Christopherson <seanjc@google.com>,
	Jim Mattson <jmattson@google.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v3 05/12] KVM: x86/mmu: allow APICv memslot to be partially enabled
Date: Tue, 3 Aug 2021 11:12:33 +0200	[thread overview]
Message-ID: <596639a1-4df3-54e7-3f72-1bd292e592a2@redhat.com> (raw)
In-Reply-To: <20210802183329.2309921-6-mlevitsk@redhat.com>

On 02/08/21 20:33, Maxim Levitsky wrote:
> on AMD, APIC virtualization needs to dynamicaly inhibit the AVIC in a
> response to some events, and this is problematic and not efficient to do by
> enabling/disabling the memslot that covers APIC's mmio range.
> Plus due to SRCU locking, it makes it more complex to request AVIC inhibition.
> 
> Instead, the APIC memslot will be always enabled, but the MMU code
> will not install a SPTE for it, when arch.apic_access_memslot_enabled == false
> and instead jump straight to emulating the access.
> 
> When inhibiting the AVIC, this SPTE will be zapped.
> 
> This code is based on a suggestion from Sean Christopherson:
> https://lkml.org/lkml/2021/7/19/2970
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>   arch/x86/kvm/mmu/mmu.c | 23 ++++++++++++++++++-----
>   1 file changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 6f77f6efd43c..965b562da893 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3857,11 +3857,24 @@ static bool kvm_faultin_pfn(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
>   	if (slot && (slot->flags & KVM_MEMSLOT_INVALID))
>   		goto out_retry;
>   
> -	/* Don't expose private memslots to L2. */
> -	if (is_guest_mode(vcpu) && !kvm_is_visible_memslot(slot)) {
> -		*pfn = KVM_PFN_NOSLOT;
> -		*writable = false;
> -		return false;
> +	if (!kvm_is_visible_memslot(slot)) {
> +		/* Don't expose private memslots to L2. */
> +		if (is_guest_mode(vcpu)) {
> +			*pfn = KVM_PFN_NOSLOT;
> +			*writable = false;
> +			return false;
> +		}
> +		/*
> +		 * If the APIC access page exists but is disabled, go directly
> +		 * to emulation without caching the MMIO access or creating a
> +		 * MMIO SPTE.  That way the cache doesn't need to be purged
> +		 * when the AVIC is re-enabled.
> +		 */
> +		if (slot && slot->id == APIC_ACCESS_PAGE_PRIVATE_MEMSLOT &&
> +		    !vcpu->kvm->arch.apic_access_memslot_enabled) {

In addition to using apicv_inhibit_reasons, I would change the subject 
to "allow APICv memslot to be enabled but invisible".  Otherwise looks good.

Paolo

> +			*r = RET_PF_EMULATE;
> +			return true;
> +		}
>   	}
>   
>   	async = false;
> 


  reply	other threads:[~2021-08-03  9:12 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-02 18:33 [PATCH v3 00/12] My AVIC patch queue Maxim Levitsky
2021-08-02 18:33 ` [PATCH v3 01/12] Revert "KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock" Maxim Levitsky
2021-08-03  8:05   ` Paolo Bonzini
2021-08-03 15:11     ` Sean Christopherson
2021-08-03 17:29       ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 02/12] KVM: x86/mmu: bump mmu notifier count in kvm_zap_gfn_range Maxim Levitsky
2021-08-03  9:00   ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 03/12] KVM: x86/mmu: rename try_async_pf to kvm_faultin_pfn Maxim Levitsky
2021-08-03  9:00   ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 04/12] KVM: x86/mmu: allow kvm_faultin_pfn to return page fault handling code Maxim Levitsky
2021-08-03  9:00   ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 05/12] KVM: x86/mmu: allow APICv memslot to be partially enabled Maxim Levitsky
2021-08-03  9:12   ` Paolo Bonzini [this message]
2021-08-02 18:33 ` [PATCH v3 06/12] KVM: x86: don't disable APICv memslot when inhibited Maxim Levitsky
2021-08-03  8:44   ` Paolo Bonzini
2021-08-09 18:51     ` Maxim Levitsky
2021-08-09 19:14       ` Sean Christopherson
2021-08-02 18:33 ` [PATCH v3 07/12] KVM: x86: APICv: fix race in kvm_request_apicv_update on SVM Maxim Levitsky
2021-08-02 18:33 ` [PATCH v3 08/12] KVM: SVM: add warning for mistmatch between AVIC state and AVIC access page state Maxim Levitsky
2021-08-03  8:45   ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 09/12] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use Maxim Levitsky
2021-08-03  8:47   ` Paolo Bonzini
2021-08-03  9:01   ` Paolo Bonzini
2021-08-03  9:11   ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 10/12] KVM: SVM: remove svm_toggle_avic_for_irq_window Maxim Levitsky
2021-08-03  9:11   ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 11/12] KVM: SVM: call avic_vcpu_load/avic_vcpu_put when enabling/disabling AVIC Maxim Levitsky
2021-08-03  9:00   ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 12/12] KVM: SVM: AVIC: drop unsupported AVIC base relocation code Maxim Levitsky

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