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

[Marcelo Tosatti]

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@xxxxxxxxxxxxxx>
> ---
>  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;

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