У вт, 2023-08-15 у 14:35 -0700, Sean Christopherson пише:
> 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@xxxxxxxxxx>
> ---
> 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));
I overall agree with this patch however the old code was safer:
svm->avic_backing_page is set to physical address of the apic registers
only in the avic_init_backing_page() and after checking the
vcpu->arch.apic->regs != NULL and now in theory NULL vcpu->arch.apic->regs
are not checked.
I know that you later add a patch which adds a similar warning, but I prefer that
you fold it with this patch.
> }
>
> 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;
>
> /*
Best regards,
Maxim Levitsky
