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Date: Tue, 9 Nov 2010 10:06:31 +0200
From: Gleb Natapov <gleb@...hat.com>
To: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc: Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 3/3] KVM: MMU: retry #PF for softmmu
On Thu, Nov 04, 2010 at 06:36:36PM +0800, Xiao Guangrong wrote:
> Retry #PF for softmmu only when the current vcpu has the same
> root shadow page as the time when #PF occurs. it means they
> have same paging environment.
>
Avi had an idea to allocate spte at the fault time, get reference
to it and populate it on completion instead of prefaulting. How hard
will it be?
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> ---
> arch/x86/include/asm/kvm_host.h | 6 ++++++
> arch/x86/kvm/mmu.c | 33 ++++++++++++++++++++++++++++++++-
> arch/x86/kvm/x86.c | 16 ++++++++++++++--
> virt/kvm/async_pf.c | 1 +
> 4 files changed, 53 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 7f20f2c..b99ef7d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -192,6 +192,8 @@ struct kvm_mmu_page {
> struct list_head link;
> struct hlist_node hash_link;
>
> + struct kref apfs_counter;
> +
> /*
> * The following two entries are used to key the shadow page in the
> * hash table.
> @@ -600,6 +602,7 @@ struct kvm_x86_ops {
> struct kvm_arch_async_pf {
> u32 token;
> gfn_t gfn;
> + struct kvm_mmu_page *root_sp;
> };
>
> extern struct kvm_x86_ops *kvm_x86_ops;
> @@ -697,6 +700,8 @@ void kvm_inject_nmi(struct kvm_vcpu *vcpu);
>
> int fx_init(struct kvm_vcpu *vcpu);
>
> +struct kvm_mmu_page *get_vcpu_root_sp(struct kvm_vcpu *vcpu, gva_t gva);
> +void kvm_mmu_release_apf_sp(struct kvm_mmu_page *sp);
> 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,
> @@ -822,6 +827,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
> void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu,
> struct kvm_async_pf *work);
> bool kvm_arch_can_inject_async_page_present(struct kvm_vcpu *vcpu);
> +void kvm_arch_clear_async_pf(struct kvm_async_pf *work);
> extern bool kvm_find_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);
>
> #endif /* _ASM_X86_KVM_HOST_H */
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index f3fad4f..60cc9f9 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -993,6 +993,19 @@ static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, int nr)
> percpu_counter_add(&kvm_total_used_mmu_pages, nr);
> }
>
> +static void free_shadow_page(struct kref *kref)
> +{
> + struct kvm_mmu_page *sp;
> +
> + sp = container_of(kref, struct kvm_mmu_page, apfs_counter);
> + kmem_cache_free(mmu_page_header_cache, sp);
> +}
> +
> +void kvm_mmu_release_apf_sp(struct kvm_mmu_page *sp)
> +{
> + kref_put(&sp->apfs_counter, free_shadow_page);;
> +}
> +
> static void kvm_mmu_free_page(struct kvm *kvm, struct kvm_mmu_page *sp)
> {
> ASSERT(is_empty_shadow_page(sp->spt));
> @@ -1001,7 +1014,7 @@ static void kvm_mmu_free_page(struct kvm *kvm, struct kvm_mmu_page *sp)
> __free_page(virt_to_page(sp->spt));
> if (!sp->role.direct)
> __free_page(virt_to_page(sp->gfns));
> - kmem_cache_free(mmu_page_header_cache, sp);
> + kvm_mmu_release_apf_sp(sp);
> kvm_mod_used_mmu_pages(kvm, -1);
> }
>
> @@ -1026,6 +1039,7 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
> sp->multimapped = 0;
> sp->parent_pte = parent_pte;
> kvm_mod_used_mmu_pages(vcpu->kvm, +1);
> + kref_init(&sp->apfs_counter);
> return sp;
> }
>
> @@ -2597,11 +2611,28 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
> error_code & PFERR_WRITE_MASK, gfn);
> }
>
> +struct kvm_mmu_page *get_vcpu_root_sp(struct kvm_vcpu *vcpu, gva_t gva)
> +{
> + struct kvm_shadow_walk_iterator iterator;
> + bool ret;
> +
> + shadow_walk_init(&iterator, vcpu, gva);
> + ret = shadow_walk_okay(&iterator);
> + WARN_ON(!ret);
> +
> + return page_header(__pa(iterator.sptep));
> +}
> +
> static int kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn)
> {
> struct kvm_arch_async_pf arch;
> +
> arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id;
> arch.gfn = gfn;
> + if (!tdp_enabled) {
> + arch.root_sp = get_vcpu_root_sp(vcpu, gva);
> + kref_get(&arch.root_sp->apfs_counter);
> + }
>
> return kvm_setup_async_pf(vcpu, gva, gfn, &arch);
> }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index aacc5eb..72d672f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6174,14 +6174,17 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
> {
> int r;
>
> - if (!tdp_enabled || is_error_page(work->page))
> + if (is_error_page(work->page))
> return;
>
> r = kvm_mmu_reload(vcpu);
> +
> if (unlikely(r))
> return;
>
> - vcpu->arch.mmu.page_fault(vcpu, work->gva, 0, true);
> + if (tdp_enabled ||
> + get_vcpu_root_sp(vcpu, work->gva) == work->arch.root_sp)
> + vcpu->arch.mmu.page_fault(vcpu, work->gva, 0, true);
> }
>
> static inline u32 kvm_async_pf_hash_fn(gfn_t gfn)
> @@ -6269,10 +6272,19 @@ void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
> }
> }
>
> +void kvm_arch_clear_async_pf(struct kvm_async_pf *work)
> +{
> + if (!tdp_enabled)
> + kvm_mmu_release_apf_sp(work->arch.root_sp);
> +}
> +
> void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
> struct kvm_async_pf *work)
> {
> trace_kvm_async_pf_ready(work->arch.token, work->gva);
> +
> + kvm_arch_clear_async_pf(work);
> +
> if (is_error_page(work->page))
> work->arch.token = ~0; /* broadcast wakeup */
> else
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index 74268b4..c3d4788 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -101,6 +101,7 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
> typeof(*work), queue);
> cancel_work_sync(&work->work);
> list_del(&work->queue);
> + kvm_arch_clear_async_pf(work);
> if (!work->done) /* work was canceled */
> kmem_cache_free(async_pf_cache, work);
> }
> --
> 1.7.0.4
--
Gleb.
--
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