KVM: MMU: Avoid calling gfn_to_page() in mmu_set_spte()

Since gfn_to_page() is a sleeping function, and we want to make the core mmu
spinlocked, we need to pass the page from the walker context (which can sleep)
to the shadow context (which cannot).

[marcelo: avoid recursive locking of mmap_sem]

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

3 files changed, 73 insertions, 10 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 3b91227969a5..c0b757be7b99 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -890,11 +890,10 @@ struct page *gva_to_page(struct kvm_vcpu *vcpu, gva_t gva)
 static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
                          unsigned pt_access, unsigned pte_access,
                          int user_fault, int write_fault, int dirty,
-                         int *ptwrite, gfn_t gfn)
+                         int *ptwrite, gfn_t gfn, struct page *page)
 {
         u64 spte;
         int was_rmapped = is_rmap_pte(*shadow_pte);
-        struct page *page;
 
         pgprintk("%s: spte %llx access %x write_fault %d"
                  " user_fault %d gfn %lx\n",
@@ -912,8 +911,6 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
         if (!(pte_access & ACC_EXEC_MASK))
                 spte |= PT64_NX_MASK;
 
-        page = gfn_to_page(vcpu->kvm, gfn);
-
         spte |= PT_PRESENT_MASK;
         if (pte_access & ACC_USER_MASK)
                 spte |= PT_USER_MASK;
@@ -979,6 +976,11 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
         int level = PT32E_ROOT_LEVEL;
         hpa_t table_addr = vcpu->arch.mmu.root_hpa;
         int pt_write = 0;
+        struct page *page;
+
+        down_read(&current->mm->mmap_sem);
+        page = gfn_to_page(vcpu->kvm, gfn);
+        up_read(&current->mm->mmap_sem);
 
         for (; ; level--) {
                 u32 index = PT64_INDEX(v, level);
@@ -989,7 +991,7 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
 
                 if (level == 1) {
                         mmu_set_spte(vcpu, &table[index], ACC_ALL, ACC_ALL,
-                                     0, write, 1, &pt_write, gfn);
+                                     0, write, 1, &pt_write, gfn, page);
                         return pt_write || is_io_pte(table[index]);
                 }
 
@@ -1005,6 +1007,7 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
                                                      NULL);
                         if (!new_table) {
                                 pgprintk("nonpaging_map: ENOMEM\n");
+                                kvm_release_page_clean(page);
                                 return -ENOMEM;
                         }
 
@@ -1347,6 +1350,43 @@ static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu)
         return !!(spte && (*spte & PT_ACCESSED_MASK));
 }
 
+static void mmu_guess_page_from_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
+                                          const u8 *new, int bytes)
+{
+        gfn_t gfn;
+        int r;
+        u64 gpte = 0;
+
+        if (bytes != 4 && bytes != 8)
+                return;
+
+        /*
+         * Assume that the pte write on a page table of the same type
+         * as the current vcpu paging mode.  This is nearly always true
+         * (might be false while changing modes).  Note it is verified later
+         * by update_pte().
+         */
+        if (is_pae(vcpu)) {
+                /* Handle a 32-bit guest writing two halves of a 64-bit gpte */
+                if ((bytes == 4) && (gpa % 4 == 0)) {
+                        r = kvm_read_guest(vcpu->kvm, gpa & ~(u64)7, &gpte, 8);
+                        if (r)
+                                return;
+                        memcpy((void *)&gpte + (gpa % 8), new, 4);
+                } else if ((bytes == 8) && (gpa % 8 == 0)) {
+                        memcpy((void *)&gpte, new, 8);
+                }
+        } else {
+                if ((bytes == 4) && (gpa % 4 == 0))
+                        memcpy((void *)&gpte, new, 4);
+        }
+        if (!is_present_pte(gpte))
+                return;
+        gfn = (gpte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+        vcpu->arch.update_pte.gfn = gfn;
+        vcpu->arch.update_pte.page = gfn_to_page(vcpu->kvm, gfn);
+}
+
 void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
                        const u8 *new, int bytes)
 {
@@ -1367,6 +1407,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
         int npte;
 
         pgprintk("%s: gpa %llx bytes %d\n", __FUNCTION__, gpa, bytes);
+        mmu_guess_page_from_pte_write(vcpu, gpa, new, bytes);
         mutex_lock(&vcpu->kvm->lock);
         ++vcpu->kvm->stat.mmu_pte_write;
         kvm_mmu_audit(vcpu, "pre pte write");
@@ -1437,6 +1478,10 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
         }
         kvm_mmu_audit(vcpu, "post pte write");
         mutex_unlock(&vcpu->kvm->lock);
+        if (vcpu->arch.update_pte.page) {
+                kvm_release_page_clean(vcpu->arch.update_pte.page);
+                vcpu->arch.update_pte.page = NULL;
+        }
 }
 
 int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 136a65d72b0a..3d7846ba26e1 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -245,6 +245,7 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
 {
         pt_element_t gpte;
         unsigned pte_access;
+        struct page *npage;
 
         gpte = *(const pt_element_t *)pte;
         if (~gpte & (PT_PRESENT_MASK | PT_ACCESSED_MASK)) {
@@ -256,8 +257,14 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
                 return;
         pgprintk("%s: gpte %llx spte %p\n", __FUNCTION__, (u64)gpte, spte);
         pte_access = page->role.access & FNAME(gpte_access)(vcpu, gpte);
+        if (gpte_to_gfn(gpte) != vcpu->arch.update_pte.gfn)
+                return;
+        npage = vcpu->arch.update_pte.page;
+        if (!npage)
+                return;
+        get_page(npage);
         mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
-                     gpte & PT_DIRTY_MASK, NULL, gpte_to_gfn(gpte));
+                     gpte & PT_DIRTY_MASK, NULL, gpte_to_gfn(gpte), npage);
 }
 
 /*
@@ -265,7 +272,8 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
  */
 static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                          struct guest_walker *walker,
-                         int user_fault, int write_fault, int *ptwrite)
+                         int user_fault, int write_fault, int *ptwrite,
+                         struct page *page)
 {
         hpa_t shadow_addr;
         int level;
@@ -321,8 +329,10 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                         r = kvm_read_guest_atomic(vcpu->kvm,
                                                   walker->pte_gpa[level - 2],
                                                   &curr_pte, sizeof(curr_pte));
-                        if (r || curr_pte != walker->ptes[level - 2])
+                        if (r || curr_pte != walker->ptes[level - 2]) {
+                                kvm_release_page_clean(page);
                                 return NULL;
+                        }
                 }
                 shadow_addr = __pa(shadow_page->spt);
                 shadow_pte = shadow_addr | PT_PRESENT_MASK | PT_ACCESSED_MASK
@@ -333,7 +343,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
         mmu_set_spte(vcpu, shadow_ent, access, walker->pte_access & access,
                      user_fault, write_fault,
                      walker->ptes[walker->level-1] & PT_DIRTY_MASK,
-                     ptwrite, walker->gfn);
+                     ptwrite, walker->gfn, page);
 
         return shadow_ent;
 }
@@ -362,6 +372,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
         u64 *shadow_pte;
         int write_pt = 0;
         int r;
+        struct page *page;
 
         pgprintk("%s: addr %lx err %x\n", __FUNCTION__, addr, error_code);
         kvm_mmu_audit(vcpu, "pre page fault");
@@ -388,9 +399,11 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
                 return 0;
         }
 
+        page = gfn_to_page(vcpu->kvm, walker.gfn);
+
         mutex_lock(&vcpu->kvm->lock);
         shadow_pte = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
-                                  &write_pt);
+                                  &write_pt, page);
         pgprintk("%s: shadow pte %p %llx ptwrite %d\n", __FUNCTION__,
                  shadow_pte, *shadow_pte, write_pt);
 
diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
index 44b89259f6c4..20597bc16744 100644
--- a/include/asm-x86/kvm_host.h
+++ b/include/asm-x86/kvm_host.h
@@ -224,6 +224,11 @@ struct kvm_vcpu_arch {
         int   last_pt_write_count;
         u64  *last_pte_updated;
 
+        struct {
+                gfn_t gfn;          /* presumed gfn during guest pte update */
+                struct page *page;  /* page corresponding to that gfn */
+        } update_pte;
+
         struct i387_fxsave_struct host_fx_image;
         struct i387_fxsave_struct guest_fx_image;