diff mbox

[v3,05/19] KVM: MMU: optimize to handle dirty bit

Message ID 4E0C320A.8080104@cn.fujitsu.com (mailing list archive)
State New, archived
Headers show

Commit Message

Xiao Guangrong June 30, 2011, 8:21 a.m. UTC 
If dirty bit is not set, we can make the pte access read-only to avoid handing
dirty bit everywhere

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
 arch/x86/kvm/mmu.c         |   13 +++++------
 arch/x86/kvm/paging_tmpl.h |   46 ++++++++++++++++++-------------------------
 2 files changed, 25 insertions(+), 34 deletions(-)

Comments

Marcelo Tosatti July 5, 2011, 7:27 p.m. UTC | #1 
On Thu, Jun 30, 2011 at 04:21:30PM +0800, Xiao Guangrong wrote:
> If dirty bit is not set, we can make the pte access read-only to avoid handing
> dirty bit everywhere
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>

> -static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
> +static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte,
> +				   bool last)
>  {
>  	unsigned access;
>  
>  	access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
> +	if (last && !is_dirty_gpte(gpte))
> +		access &= ~ACC_WRITE_MASK;
> +

What if the walker marks the dirty bit on the gpte?

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Xiao Guangrong July 6, 2011, 1:22 a.m. UTC | #2 
On 07/06/2011 03:27 AM, Marcelo Tosatti wrote:
> On Thu, Jun 30, 2011 at 04:21:30PM +0800, Xiao Guangrong wrote:
>> If dirty bit is not set, we can make the pte access read-only to avoid handing
>> dirty bit everywhere
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
> 
>> -static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
>> +static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte,
>> +				   bool last)
>>  {
>>  	unsigned access;
>>  
>>  	access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
>> +	if (last && !is_dirty_gpte(gpte))
>> +		access &= ~ACC_WRITE_MASK;
>> +
> 
> What if the walker marks the dirty bit on the gpte?
> 

Actually, we get guest pte access after mark the dirty bit:

	if (write_fault && unlikely(!is_dirty_gpte(pte))) {
		int ret;

		trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
		ret = FNAME(cmpxchg_gpte)(vcpu, mmu, ptep_user, index,
					  pte, pte|PT_DIRTY_MASK);
		if (unlikely(ret < 0)) {
			present = false;
			goto error;
		} else if (ret)
			goto walk;

		mark_page_dirty(vcpu->kvm, table_gfn);
		pte |= PT_DIRTY_MASK;
		walker->ptes[walker->level - 1] = pte;
	}

	pte_access = pt_access & FNAME(gpte_access)(vcpu, pte, true);
 
So, i think it works well :-)
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Marcelo Tosatti July 6, 2011, 4:51 p.m. UTC | #3 
On Wed, Jul 06, 2011 at 09:22:28AM +0800, Xiao Guangrong wrote:
> On 07/06/2011 03:27 AM, Marcelo Tosatti wrote:
> > On Thu, Jun 30, 2011 at 04:21:30PM +0800, Xiao Guangrong wrote:
> >> If dirty bit is not set, we can make the pte access read-only to avoid handing
> >> dirty bit everywhere
> >>
> >> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
> > 
> >> -static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
> >> +static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte,
> >> +				   bool last)
> >>  {
> >>  	unsigned access;
> >>  
> >>  	access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
> >> +	if (last && !is_dirty_gpte(gpte))
> >> +		access &= ~ACC_WRITE_MASK;
> >> +
> > 
> > What if the walker marks the dirty bit on the gpte?
> > 
> 
> Actually, we get guest pte access after mark the dirty bit:
> 
> 	if (write_fault && unlikely(!is_dirty_gpte(pte))) {
> 		int ret;
> 
> 		trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
> 		ret = FNAME(cmpxchg_gpte)(vcpu, mmu, ptep_user, index,
> 					  pte, pte|PT_DIRTY_MASK);
> 		if (unlikely(ret < 0)) {
> 			present = false;
> 			goto error;
> 		} else if (ret)
> 			goto walk;
> 
> 		mark_page_dirty(vcpu->kvm, table_gfn);
> 		pte |= PT_DIRTY_MASK;
> 		walker->ptes[walker->level - 1] = pte;
> 	}
> 
> 	pte_access = pt_access & FNAME(gpte_access)(vcpu, pte, true);
>  
> So, i think it works well :-)

I think you meant after marking the accessed bit. The dirty bit is set
just before returning.

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Xiao Guangrong July 6, 2011, 7:12 p.m. UTC | #4 
On 07/07/2011 12:51 AM, Marcelo Tosatti wrote:
> On Wed, Jul 06, 2011 at 09:22:28AM +0800, Xiao Guangrong wrote:
>> On 07/06/2011 03:27 AM, Marcelo Tosatti wrote:
>>> On Thu, Jun 30, 2011 at 04:21:30PM +0800, Xiao Guangrong wrote:
>>>> If dirty bit is not set, we can make the pte access read-only to avoid handing
>>>> dirty bit everywhere
>>>>
>>>> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
>>>
>>>> -static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
>>>> +static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte,
>>>> +				   bool last)
>>>>  {
>>>>  	unsigned access;
>>>>  
>>>>  	access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
>>>> +	if (last && !is_dirty_gpte(gpte))
>>>> +		access &= ~ACC_WRITE_MASK;
>>>> +
>>>
>>> What if the walker marks the dirty bit on the gpte?
>>>
>>
>> Actually, we get guest pte access after mark the dirty bit:
>>
>> 	if (write_fault && unlikely(!is_dirty_gpte(pte))) {
>> 		int ret;
>>
>> 		trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
>> 		ret = FNAME(cmpxchg_gpte)(vcpu, mmu, ptep_user, index,
>> 					  pte, pte|PT_DIRTY_MASK);
>> 		if (unlikely(ret < 0)) {
>> 			present = false;
>> 			goto error;
>> 		} else if (ret)
>> 			goto walk;
>>
>> 		mark_page_dirty(vcpu->kvm, table_gfn);
>> 		pte |= PT_DIRTY_MASK;
>> 		walker->ptes[walker->level - 1] = pte;
>> 	}
>>
>> 	pte_access = pt_access & FNAME(gpte_access)(vcpu, pte, true);
>>  
>> So, i think it works well :-)
> 
> I think you meant after marking the accessed bit. The dirty bit is set
> just before returning.
> 

In this patch, i moved getting pte_access to the behind of setting dirty bit set
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Marcelo Tosatti July 7, 2011, 8:15 a.m. UTC | #5 
On Thu, Jul 07, 2011 at 03:12:26AM +0800, Xiao Guangrong wrote:
> >> So, i think it works well :-)
> > 
> > I think you meant after marking the accessed bit. The dirty bit is set
> > just before returning.
> > 
> 
> In this patch, i moved getting pte_access to the behind of setting dirty bit set

OK

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diff mbox

Patch

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index d1986b7..98812c2 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1923,7 +1923,7 @@  static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
 
 static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		    unsigned pte_access, int user_fault,
-		    int write_fault, int dirty, int level,
+		    int write_fault, int level,
 		    gfn_t gfn, pfn_t pfn, bool speculative,
 		    bool can_unsync, bool host_writable)
 {
@@ -1938,8 +1938,7 @@  static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 	spte = PT_PRESENT_MASK;
 	if (!speculative)
 		spte |= shadow_accessed_mask;
-	if (!dirty)
-		pte_access &= ~ACC_WRITE_MASK;
+
 	if (pte_access & ACC_EXEC_MASK)
 		spte |= shadow_x_mask;
 	else
@@ -2023,7 +2022,7 @@  done:
 
 static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 			 unsigned pt_access, unsigned pte_access,
-			 int user_fault, int write_fault, int dirty,
+			 int user_fault, int write_fault,
 			 int *ptwrite, int level, gfn_t gfn,
 			 pfn_t pfn, bool speculative,
 			 bool host_writable)
@@ -2059,7 +2058,7 @@  static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 	}
 
 	if (set_spte(vcpu, sptep, pte_access, user_fault, write_fault,
-		      dirty, level, gfn, pfn, speculative, true,
+		      level, gfn, pfn, speculative, true,
 		      host_writable)) {
 		if (write_fault)
 			*ptwrite = 1;
@@ -2129,7 +2128,7 @@  static int direct_pte_prefetch_many(struct kvm_vcpu *vcpu,
 
 	for (i = 0; i < ret; i++, gfn++, start++)
 		mmu_set_spte(vcpu, start, ACC_ALL,
-			     access, 0, 0, 1, NULL,
+			     access, 0, 0, NULL,
 			     sp->role.level, gfn,
 			     page_to_pfn(pages[i]), true, true);
 
@@ -2193,7 +2192,7 @@  static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
 			unsigned pte_access = ACC_ALL;
 
 			mmu_set_spte(vcpu, iterator.sptep, ACC_ALL, pte_access,
-				     0, write, 1, &pt_write,
+				     0, write, &pt_write,
 				     level, gfn, pfn, prefault, map_writable);
 			direct_pte_prefetch(vcpu, iterator.sptep);
 			++vcpu->stat.pf_fixed;
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 13978dc..e06c9e4 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -101,11 +101,15 @@  static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 	return (ret != orig_pte);
 }
 
-static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
+static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte,
+				   bool last)
 {
 	unsigned access;
 
 	access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
+	if (last && !is_dirty_gpte(gpte))
+		access &= ~ACC_WRITE_MASK;
+
 #if PTTYPE == 64
 	if (vcpu->arch.mmu.nx)
 		access &= ~(gpte >> PT64_NX_SHIFT);
@@ -227,8 +231,6 @@  walk:
 			pte |= PT_ACCESSED_MASK;
 		}
 
-		pte_access = pt_access & FNAME(gpte_access)(vcpu, pte);
-
 		walker->ptes[walker->level - 1] = pte;
 
 		if ((walker->level == PT_PAGE_TABLE_LEVEL) ||
@@ -269,7 +271,7 @@  walk:
 			break;
 		}
 
-		pt_access = pte_access;
+		pt_access &= FNAME(gpte_access)(vcpu, pte, false);
 		--walker->level;
 	}
 
@@ -293,6 +295,7 @@  walk:
 		walker->ptes[walker->level - 1] = pte;
 	}
 
+	pte_access = pt_access & FNAME(gpte_access)(vcpu, pte, true);
 	walker->pt_access = pt_access;
 	walker->pte_access = pte_access;
 	pgprintk("%s: pte %llx pte_access %x pt_access %x\n",
@@ -373,7 +376,7 @@  static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
 		return;
 
 	pgprintk("%s: gpte %llx spte %p\n", __func__, (u64)gpte, spte);
-	pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
+	pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte, true);
 	pfn = gfn_to_pfn_atomic(vcpu->kvm, gpte_to_gfn(gpte));
 	if (is_error_pfn(pfn)) {
 		kvm_release_pfn_clean(pfn);
@@ -385,7 +388,7 @@  static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
 	 * vcpu->arch.update_pte.pfn was fetched from get_user_pages(write = 1).
 	 */
 	mmu_set_spte(vcpu, spte, sp->role.access, pte_access, 0, 0,
-		     is_dirty_gpte(gpte), NULL, PT_PAGE_TABLE_LEVEL,
+		     NULL, PT_PAGE_TABLE_LEVEL,
 		     gpte_to_gfn(gpte), pfn, true, true);
 }
 
@@ -436,7 +439,6 @@  static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
 		unsigned pte_access;
 		gfn_t gfn;
 		pfn_t pfn;
-		bool dirty;
 
 		if (spte == sptep)
 			continue;
@@ -449,18 +451,18 @@  static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
 		if (FNAME(prefetch_invalid_gpte)(vcpu, sp, spte, gpte))
 			continue;
 
-		pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
+		pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte,
+								  true);
 		gfn = gpte_to_gfn(gpte);
-		dirty = is_dirty_gpte(gpte);
 		pfn = pte_prefetch_gfn_to_pfn(vcpu, gfn,
-				      (pte_access & ACC_WRITE_MASK) && dirty);
+				      pte_access & ACC_WRITE_MASK);
 		if (is_error_pfn(pfn)) {
 			kvm_release_pfn_clean(pfn);
 			break;
 		}
 
 		mmu_set_spte(vcpu, spte, sp->role.access, pte_access, 0, 0,
-			     dirty, NULL, PT_PAGE_TABLE_LEVEL, gfn,
+			     NULL, PT_PAGE_TABLE_LEVEL, gfn,
 			     pfn, true, true);
 	}
 }
@@ -476,7 +478,6 @@  static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 {
 	unsigned access = gw->pt_access;
 	struct kvm_mmu_page *sp = NULL;
-	bool dirty = is_dirty_gpte(gw->ptes[gw->level - 1]);
 	int top_level;
 	unsigned direct_access;
 	struct kvm_shadow_walk_iterator it;
@@ -485,8 +486,6 @@  static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 		return NULL;
 
 	direct_access = gw->pt_access & gw->pte_access;
-	if (!dirty)
-		direct_access &= ~ACC_WRITE_MASK;
 
 	top_level = vcpu->arch.mmu.root_level;
 	if (top_level == PT32E_ROOT_LEVEL)
@@ -545,7 +544,7 @@  static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 	}
 
 	mmu_set_spte(vcpu, it.sptep, access, gw->pte_access & access,
-		     user_fault, write_fault, dirty, ptwrite, it.level,
+		     user_fault, write_fault, ptwrite, it.level,
 		     gw->gfn, pfn, prefault, map_writable);
 	FNAME(pte_prefetch)(vcpu, gw, it.sptep);
 
@@ -628,17 +627,9 @@  static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 		return 0;
 
 	/* mmio */
-	if (is_error_pfn(pfn)) {
-		unsigned access = walker.pte_access;
-		bool dirty = is_dirty_gpte(walker.ptes[walker.level - 1]);
-
-		if (dirty)
-			access &= ~ACC_WRITE_MASK;
-
+	if (is_error_pfn(pfn))
 		return kvm_handle_bad_page(vcpu, mmu_is_nested(vcpu) ? 0 :
-					   addr, access, walker.gfn, pfn);
-	}
-
+				      addr, walker.pte_access, walker.gfn, pfn);
 	spin_lock(&vcpu->kvm->mmu_lock);
 	if (mmu_notifier_retry(vcpu, mmu_seq))
 		goto out_unlock;
@@ -855,11 +846,12 @@  static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 		}
 
 		nr_present++;
-		pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
+		pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte,
+								  true);
 		host_writable = sp->spt[i] & SPTE_HOST_WRITEABLE;
 
 		set_spte(vcpu, &sp->spt[i], pte_access, 0, 0,
-			 is_dirty_gpte(gpte), PT_PAGE_TABLE_LEVEL, gfn,
+			 PT_PAGE_TABLE_LEVEL, gfn,
 			 spte_to_pfn(sp->spt[i]), true, false,
 			 host_writable);
 	}