linux-kernel - [PATCH 05/10] KVM: SVM: Drop vcpu_svm's pointless avic_backing

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Message-ID: <20230815213533.548732-6-seanjc@google.com>
Date:   Tue, 15 Aug 2023 14:35:28 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     kvm@...r.kernel.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 05/10] KVM: SVM: Drop vcpu_svm's pointless avic_backing_page field

Drop vcpu_svm's avic_backing_page pointer and instead grab the physical
address of KVM's vAPIC page directly from the source.  Getting a physical
address from a kernel virtual address is not an expensive operation, and
getting the physical address from a struct page is *more* expensive for
CONFIG_SPARSEMEM=y kernels.  Regardless, none of the paths that consume
the address are hot paths, i.e. shaving cycles is not a priority.

Eliminating the "cache" means KVM doesn't have to worry about the cache
being invalid, which will simplify a future fix when dealing with vCPU IDs
that are too big.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/avic.c | 4 +---
 arch/x86/kvm/svm/svm.h  | 1 -
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 954bdb45033b..e49b682c8469 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -243,7 +243,7 @@ int avic_vm_init(struct kvm *kvm)
 
 static phys_addr_t avic_get_backing_page_address(struct vcpu_svm *svm)
 {
-	return __sme_set(page_to_phys(svm->avic_backing_page));
+	return __sme_set(__pa(svm->vcpu.arch.apic->regs));
 }
 
 void avic_init_vmcb(struct vcpu_svm *svm, struct vmcb *vmcb)
@@ -305,8 +305,6 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
 			return ret;
 	}
 
-	svm->avic_backing_page = virt_to_page(vcpu->arch.apic->regs);
-
 	/* Setting AVIC backing page address in the phy APIC ID table */
 	entry = avic_get_physical_id_entry(vcpu, id);
 	if (!entry)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 2237230aad98..a9fde1bb85ee 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -261,7 +261,6 @@ struct vcpu_svm {
 
 	u32 ldr_reg;
 	u32 dfr_reg;
-	struct page *avic_backing_page;
 	u64 *avic_physical_id_cache;
 
 	/*
-- 
2.41.0.694.ge786442a9b-goog