Re: [PATCH 07/11] KVM: MMU: fast prefetch spte on invlpg path

Marcelo Tosatti
2011-08-23T01:05:45Z

On Tue, Aug 16, 2011 at 02:44:42PM +0800, Xiao Guangrong wrote:
> Fast prefetch spte for the unsync shadow page on invlpg path
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
> ---
> arch/x86/include/asm/kvm_host.h | 4 +---
> arch/x86/kvm/mmu.c | 38 +++++++++++++++-----------------------
> arch/x86/kvm/paging_tmpl.h | 30 ++++++++++++++++++------------
> arch/x86/kvm/x86.c | 4 ++--
> 4 files changed, 36 insertions(+), 40 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 58ea3a7..927ba73 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -460,7 +460,6 @@ struct kvm_arch {
> unsigned int n_requested_mmu_pages;
> unsigned int n_max_mmu_pages;
> unsigned int indirect_shadow_pages;
> - atomic_t invlpg_counter;
> struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];
> /*
> * Hash table of struct kvm_mmu_page.
> @@ -754,8 +753,7 @@ int fx_init(struct kvm_vcpu *vcpu);
>
> void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu);
> void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
> - const u8 *new, int bytes,
> - bool guest_initiated);
> + const u8 *new, int bytes);
> int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn);
> int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva);
> void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu);
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index ed3e778..f6de2fc 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3530,8 +3530,7 @@ static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu)
> }
>
> void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
> - const u8 *new, int bytes,
> - bool guest_initiated)
> + const u8 *new, int bytes)
> {
> gfn_t gfn = gpa >> PAGE_SHIFT;
> union kvm_mmu_page_role mask = { .word = 0 };
> @@ -3540,7 +3539,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
> LIST_HEAD(invalid_list);
> u64 entry, gentry, *spte;
> unsigned pte_size, page_offset, misaligned, quadrant, offset;
> - int level, npte, invlpg_counter, r, flooded = 0;
> + int level, npte, r, flooded = 0;
> bool remote_flush, local_flush, zap_page;
>
> /*
> @@ -3555,19 +3554,16 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
>
> pgprintk("%s: gpa %llx bytes %d\n", __func__, gpa, bytes);
>
> - invlpg_counter = atomic_read(&vcpu->kvm->arch.invlpg_counter);
> -
> /*
> * Assume that the pte write on a page table of the same type
> * as the current vcpu paging mode since we update the sptes only
> * when they have the same mode.
> */
> - if ((is_pae(vcpu) && bytes == 4) || !new) {
> + if (is_pae(vcpu) && bytes == 4) {
> /* Handle a 32-bit guest writing two halves of a 64-bit gpte */
> - if (is_pae(vcpu)) {
> - gpa &= ~(gpa_t)7;
> - bytes = 8;
> - }
> + gpa &= ~(gpa_t)7;
> + bytes = 8;
> +
> r = kvm_read_guest(vcpu->kvm, gpa, &gentry, min(bytes, 8));
> if (r)
> gentry = 0;
> @@ -3593,22 +3589,18 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
> */
> mmu_topup_memory_caches(vcpu);
> spin_lock(&vcpu->kvm->mmu_lock);
> - if (atomic_read(&vcpu->kvm->arch.invlpg_counter) != invlpg_counter)
> - gentry = 0;
> kvm_mmu_free_some_pages(vcpu);
> ++vcpu->kvm->stat.mmu_pte_write;
> trace_kvm_mmu_audit(vcpu, AUDIT_PRE_PTE_WRITE);
> - if (guest_initiated) {
> - if (gfn == vcpu->arch.last_pt_write_gfn
> - && !last_updated_pte_accessed(vcpu)) {
> - ++vcpu->arch.last_pt_write_count;
> - if (vcpu->arch.last_pt_write_count >= 3)
> - flooded = 1;
> - } else {
> - vcpu->arch.last_pt_write_gfn = gfn;
> - vcpu->arch.last_pt_write_count = 1;
> - vcpu->arch.last_pte_updated = NULL;
> - }
> + if (gfn == vcpu->arch.last_pt_write_gfn
> + && !last_updated_pte_accessed(vcpu)) {
> + ++vcpu->arch.last_pt_write_count;
> + if (vcpu->arch.last_pt_write_count >= 3)
> + flooded = 1;
> + } else {
> + vcpu->arch.last_pt_write_gfn = gfn;
> + vcpu->arch.last_pt_write_count = 1;
> + vcpu->arch.last_pte_updated = NULL;
> }
>
> mask.cr0_wp = mask.cr4_pae = mask.nxe = 1;
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 7862c05..bdc2241 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -670,20 +670,27 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
> {
> struct kvm_shadow_walk_iterator iterator;
> struct kvm_mmu_page *sp;
> - gpa_t pte_gpa = -1;
> int level;
> u64 *sptep;
>
> vcpu_clear_mmio_info(vcpu, gva);
>
> - spin_lock(&vcpu->kvm->mmu_lock);
> + /*
> + * No need to check return value here, rmap_can_add() can
> + * help us to skip pte prefetch later.
> + */
> + mmu_topup_memory_caches(vcpu);
>
> + spin_lock(&vcpu->kvm->mmu_lock);
> for_each_shadow_entry(vcpu, gva, iterator) {
> level = iterator.level;
> sptep = iterator.sptep;
>
> sp = page_header(__pa(sptep));
> if (is_last_spte(*sptep, level)) {
> + pt_element_t gpte;
> + gpa_t pte_gpa;
> +
> if (!sp->unsync)
> break;
>
> @@ -692,22 +699,21 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
>
> if (mmu_page_zap_pte(vcpu->kvm, sp, sptep))
> kvm_flush_remote_tlbs(vcpu->kvm);
> +
> + if (rmap_can_add(vcpu))
> + break;

if (!rmap_can_add(vcpu))
break;

?

> +
> + if (kvm_read_guest_atomic(vcpu->kvm, pte_gpa, &gpte,
> + sizeof(pt_element_t)))
> + break;
> +
> + FNAME(update_pte)(vcpu, sp, sptep, &gpte);
> }
>
> if (!is_shadow_present_pte(*sptep) || !sp->unsync_children)
> break;