----- junaids@xxxxxxxxxx wrote:
> When the guest indicates that the TLB doesn't need to be flushed in a
> CR3 switch, we can also skip resyncing the shadow page tables since
> an
> out-of-sync shadow page table is equivalent to an out-of-sync TLB.
>
> Signed-off-by: Junaid Shahid <junaids@xxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 39 ++++++++++++++++++++++++++++++++++++---
> arch/x86/kvm/vmx.c | 9 ++++++---
> arch/x86/kvm/x86.c | 6 +++---
> 3 files changed, 45 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 8b3229f8ae71..160dc84c15be 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -4068,7 +4068,18 @@ static bool fast_cr3_switch(struct kvm_vcpu
> *vcpu, gpa_t old_cr3,
> * have set here and allocate a new one.
> */
>
> - kvm_mmu_sync_roots(vcpu);
> + if (!skip_tlb_flush)
> + kvm_mmu_sync_roots(vcpu);
> +
> + /*
> + * The last MMIO access's GVA and GPA are cached in the
> + * VCPU. When switching to a new CR3, that GVA->GPA
> + * mapping may no longer be valid. So clear any cached
> + * MMIO info even when we don't need to sync the shadow
> + * page tables.
> + */
> + vcpu_clear_mmio_info(vcpu, MMIO_GVA_ANY);
> +
> __clear_sp_write_flooding_count(
> page_header(mmu->root_hpa));
> mmu->set_cr3(vcpu, mmu->root_hpa | pcid,
> @@ -5140,6 +5151,21 @@ void kvm_mmu_invlpg(struct kvm_vcpu *vcpu,
> gva_t gva)
> struct kvm_mmu *mmu = &vcpu->arch.mmu;
>
> mmu->invlpg(vcpu, gva, mmu->root_hpa);
> +
> + /*
> + * INVLPG is required to invalidate any global mappings for the VA,
> + * irrespective of PCID. Since it would take us roughly similar
> amount
> + * of work to determine whether the prev_cr3 mapping of the VA is
> marked
> + * global, or to just sync it blindly, so we might as well just
> always
> + * sync it.
> + *
> + * Mappings not reachable via the current cr3 or the prev_cr3 will
> be
> + * synced when switching to that cr3, so nothing needs to be done
> here
> + * for them.
> + */
> + if (VALID_PAGE(mmu->prev_root_hpa))
> + mmu->invlpg(vcpu, gva, mmu->prev_root_hpa);
> +
> kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
> ++vcpu->stat.invlpg;
> }
> @@ -5154,11 +5180,18 @@ void kvm_mmu_invpcid_gva(struct kvm_vcpu
> *vcpu, gva_t gva, unsigned long pcid)
> kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
> }
>
> + if (VALID_PAGE(mmu->prev_root_hpa) &&
> + pcid == kvm_get_pcid(vcpu, mmu->prev_cr3)) {
> + mmu->invlpg(vcpu, gva, mmu->prev_root_hpa);
> + kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
> + }
> +
I think that KVM_REQ_TLB_FLUSH was needed for prev PCID as part of patch 8.
This will solve the issue I mentioned there of breaking INVPCID handling.
> ++vcpu->stat.invlpg;
>
> /*
> - * Mappings not reachable via the current cr3 will be synced when
> - * switching to that cr3, so nothing needs to be done here for
> them.
> + * Mappings not reachable via the current cr3 or the prev_cr3 will
> be
> + * synced when switching to that cr3, so nothing needs to be done
> here
> + * for them.
> */
> }
> EXPORT_SYMBOL_GPL(kvm_mmu_invpcid_gva);
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 234498e0000f..b11ec063564f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8422,10 +8422,13 @@ static int handle_invpcid(struct kvm_vcpu
> *vcpu)
> kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
> }
>
> + if (kvm_get_pcid(vcpu, vcpu->arch.mmu.prev_cr3) == operand.pcid)
> + kvm_mmu_free_roots(vcpu, KVM_MMU_ROOT_PREVIOUS);
> +
> /*
> - * If the current cr3 does not use the given PCID, then nothing
> - * needs to be done here because a resync will happen anyway
> - * before switching to any other CR3.
> + * If neither the current cr3 nor the prev_cr3 use the given
> + * PCID, then nothing needs to be done here because a resync
> + * will happen anyway before switching to any other CR3.
> */
>
> skip_emulated_instruction(vcpu);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index baeb8447ede2..7b7da35f1ea6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -855,10 +855,10 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned
> long cr3)
> #endif
>
> if (cr3 == old_cr3 && !pdptrs_changed(vcpu)) {
> - kvm_mmu_sync_roots(vcpu);
> -
> - if (!skip_tlb_flush)
> + if (!skip_tlb_flush) {
> + kvm_mmu_sync_roots(vcpu);
> kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
> + }
> return 0;
> }
>
> --
> 2.17.0.441.gb46fe60e1d-goog
