linux-kernel - [PATCH v12 50/84] KVM: VMX: Use __kvm_faultin

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Message-ID: <20240726235234.228822-51-seanjc@google.com>
Date: Fri, 26 Jul 2024 16:51:59 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Tianrui Zhao <zhaotianrui@...ngson.cn>, 
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>, 
	Michael Ellerman <mpe@...erman.id.au>, Anup Patel <anup@...infault.org>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Janosch Frank <frankja@...ux.ibm.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, 
	Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, loongarch@...ts.linux.dev, linux-mips@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>, David Stevens <stevensd@...omium.org>
Subject: [PATCH v12 50/84] KVM: VMX: Use __kvm_faultin_page() to get APIC
 access page/pfn

Use __kvm_faultin_page() get the APIC access page so that KVM can
precisely release the refcounted page, i.e. to remove yet another user
of kvm_pfn_to_refcounted_page().  While the path isn't handling a guest
page fault, the semantics are effectively the same; KVM just happens to
be mapping the pfn into a VMCS field instead of a secondary MMU.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 30032585f7dc..b109bd282a52 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6786,8 +6786,10 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_memslots *slots = kvm_memslots(kvm);
 	struct kvm_memory_slot *slot;
+	struct page *refcounted_page;
 	unsigned long mmu_seq;
 	kvm_pfn_t pfn;
+	bool ign;
 
 	/* Defer reload until vmcs01 is the current VMCS. */
 	if (is_guest_mode(vcpu)) {
@@ -6823,7 +6825,7 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
 	 * controls the APIC-access page memslot, and only deletes the memslot
 	 * if APICv is permanently inhibited, i.e. the memslot won't reappear.
 	 */
-	pfn = gfn_to_pfn_memslot(slot, gfn);
+	pfn = __kvm_faultin_pfn(slot, gfn, FOLL_WRITE, &ign, &refcounted_page);
 	if (is_error_noslot_pfn(pfn))
 		return;
 
@@ -6834,10 +6836,13 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
 		vmcs_write64(APIC_ACCESS_ADDR, pfn_to_hpa(pfn));
 
 	/*
-	 * Do not pin apic access page in memory, the MMU notifier
-	 * will call us again if it is migrated or swapped out.
+	 * Do not pin the APIC access page in memory so that it can be freely
+	 * migrated, the MMU notifier will call us again if it is migrated or
+	 * swapped out.  KVM backs the memslot with anonymous memory, the pfn
+	 * should always point at a refcounted page (if the pfn is valid).
 	 */
-	kvm_release_pfn_clean(pfn);
+	if (!WARN_ON_ONCE(!refcounted_page))
+		kvm_release_page_clean(refcounted_page);
 
 	/*
 	 * No need for a manual TLB flush at this point, KVM has already done a
-- 
2.46.0.rc1.232.g9752f9e123-goog