KVM: MMU: optimize to handle dirty bit

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>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 25 insertions, 34 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index d1986b7dcec7..98812c25727b 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 f0fb1a4c522d..c9fe97bd8c82 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);
@@ -232,8 +236,6 @@ retry_walk:
                         pte |= PT_ACCESSED_MASK;
                 }
 
-                pte_access = pt_access & FNAME(gpte_access)(vcpu, pte);
-
                 walker->ptes[walker->level - 1] = pte;
 
                 if (FNAME(is_last_gpte)(walker, vcpu, mmu, pte)) {
@@ -268,7 +270,7 @@ retry_walk:
                         break;
                 }
 
-                pt_access = pte_access;
+                pt_access &= FNAME(gpte_access)(vcpu, pte, false);
                 --walker->level;
         }
 
@@ -293,6 +295,7 @@ retry_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",
@@ -367,7 +370,7 @@ 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);
@@ -379,7 +382,7 @@ 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);
 }
 
@@ -430,7 +433,6 @@ 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;
@@ -443,18 +445,18 @@ 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);
         }
 }
@@ -470,7 +472,6 @@ 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;
@@ -479,8 +480,6 @@ 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)
@@ -539,7 +538,7 @@ 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);
 
@@ -622,17 +621,9 @@ 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;
@@ -849,11 +840,12 @@ 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);
         }