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From: Maxim Levitsky <mlevitsk@redhat.com>
To: 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>,
	x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
	linux-kernel@vger.kernel.org (open list:X86 ARCHITECTURE (32-BIT
	AND 64-BIT)),
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Maxim Levitsky <mlevitsk@redhat.com>
Subject: [PATCH v3 05/12] KVM: x86/mmu: allow APICv memslot to be partially enabled
Date: Mon,  2 Aug 2021 21:33:22 +0300	[thread overview]
Message-ID: <20210802183329.2309921-6-mlevitsk@redhat.com> (raw)
In-Reply-To: <20210802183329.2309921-1-mlevitsk@redhat.com>

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) {
+			*r = RET_PF_EMULATE;
+			return true;
+		}
 	}
 
 	async = false;
-- 
2.26.3


  parent reply	other threads:[~2021-08-02 18:34 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 ` Maxim Levitsky [this message]
2021-08-03  9:12   ` [PATCH v3 05/12] KVM: x86/mmu: allow APICv memslot to be partially enabled Paolo Bonzini
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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