From: Sean Christopherson Date: Wed, 11 Jun 2025 22:45:14 +0000 (-0700) Subject: KVM: SVM: Drop vcpu_svm's pointless avic_backing_page field X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d8527f133c0a810b2e803a03aa186cfef721fbf8;p=thirdparty%2Fkernel%2Fstable.git 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. WARN if KVM attempts to allocate a vCPU's AVIC backing page without an in-kernel local APIC. avic_init_vcpu() bails early if the APIC is not in-kernel, and KVM disallows enabling an in-kernel APIC after vCPUs have been created, i.e. it should be impossible to reach avic_init_backing_page() without the vAPIC being allocated. Tested-by: Sairaj Kodilkar Reviewed-by: Naveen N Rao (AMD) Link: https://lore.kernel.org/r/20250611224604.313496-13-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c index 75317c189409..f0401c1e355c 100644 --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -237,7 +237,7 @@ free_avic: 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) @@ -282,7 +282,7 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu) (id > X2AVIC_MAX_PHYSICAL_ID)) return -EINVAL; - if (!vcpu->arch.apic->regs) + if (WARN_ON_ONCE(!vcpu->arch.apic->regs)) return -EINVAL; if (kvm_apicv_activated(vcpu->kvm)) { @@ -299,8 +299,6 @@ 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 cc27877d69ae..1585288200f4 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -306,7 +306,6 @@ struct vcpu_svm { u32 ldr_reg; u32 dfr_reg; - struct page *avic_backing_page; u64 *avic_physical_id_cache; /*