KVM: MMU: Simplify calculation of pte access

The nx bit is awkwardly placed in the 63rd bit position; furthermore it
has a reversed meaning compared to the other bits, which means we can't use
a bitwise and to calculate compounded access masks.

So, we simplify things by creating a new 3-bit exec/write/user access word,
and doing all calculations in that.

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

2 files changed, 43 insertions, 29 deletions

diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index 62a74151f847..f8a2137c64a2 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -85,7 +85,8 @@ static int dbg = 1;
 #define PT_PAGE_SIZE_MASK (1ULL << 7)
 #define PT_PAT_MASK (1ULL << 7)
 #define PT_GLOBAL_MASK (1ULL << 8)
-#define PT64_NX_MASK (1ULL << 63)
+#define PT64_NX_SHIFT 63
+#define PT64_NX_MASK (1ULL << PT64_NX_SHIFT)
 
 #define PT_PAT_SHIFT 7
 #define PT_DIR_PAT_SHIFT 12
@@ -153,6 +154,11 @@ static int dbg = 1;
 
 #define RMAP_EXT 4
 
+#define ACC_EXEC_MASK    1
+#define ACC_WRITE_MASK   PT_WRITABLE_MASK
+#define ACC_USER_MASK    PT_USER_MASK
+#define ACC_ALL          (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
+
 struct kvm_rmap_desc {
         u64 *shadow_ptes[RMAP_EXT];
         struct kvm_rmap_desc *more;
@@ -921,7 +927,7 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, struct page *page)
                                 >> PAGE_SHIFT;
                         new_table = kvm_mmu_get_page(vcpu, pseudo_gfn,
                                                      v, level - 1,
-                                                     1, 3, &table[index]);
+                                                     1, ACC_ALL, &table[index]);
                         if (!new_table) {
                                 pgprintk("nonpaging_map: ENOMEM\n");
                                 kvm_release_page_clean(page);
@@ -988,7 +994,7 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
 
                 ASSERT(!VALID_PAGE(root));
                 sp = kvm_mmu_get_page(vcpu, root_gfn, 0,
-                                      PT64_ROOT_LEVEL, 0, 0, NULL);
+                                      PT64_ROOT_LEVEL, 0, ACC_ALL, NULL);
                 root = __pa(sp->spt);
                 ++sp->root_count;
                 vcpu->mmu.root_hpa = root;
@@ -1009,7 +1015,7 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
                         root_gfn = 0;
                 sp = kvm_mmu_get_page(vcpu, root_gfn, i << 30,
                                       PT32_ROOT_LEVEL, !is_paging(vcpu),
-                                      0, NULL);
+                                      ACC_ALL, NULL);
                 root = __pa(sp->spt);
                 ++sp->root_count;
                 vcpu->mmu.pae_root[i] = root | PT_PRESENT_MASK;
diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h
index 8086f827120f..7688cbf413c8 100644
--- a/drivers/kvm/paging_tmpl.h
+++ b/drivers/kvm/paging_tmpl.h
@@ -66,7 +66,8 @@ struct guest_walker {
         int level;
         gfn_t table_gfn[PT_MAX_FULL_LEVELS];
         pt_element_t pte;
-        pt_element_t inherited_ar;
+        unsigned pt_access;
+        unsigned pte_access;
         gfn_t gfn;
         u32 error_code;
 };
@@ -110,7 +111,7 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
 {
         pt_element_t pte;
         gfn_t table_gfn;
-        unsigned index;
+        unsigned index, pt_access, pte_access;
         gpa_t pte_gpa;
 
         pgprintk("%s: addr %lx\n", __FUNCTION__, addr);
@@ -128,7 +129,7 @@ walk:
         ASSERT((!is_long_mode(vcpu) && is_pae(vcpu)) ||
                (vcpu->cr3 & CR3_NONPAE_RESERVED_BITS) == 0);
 
-        walker->inherited_ar = PT_USER_MASK | PT_WRITABLE_MASK;
+        pt_access = ACC_ALL;
 
         for (;;) {
                 index = PT_INDEX(addr, walker->level);
@@ -165,6 +166,14 @@ walk:
                         pte |= PT_ACCESSED_MASK;
                 }
 
+                pte_access = pte & (PT_WRITABLE_MASK | PT_USER_MASK);
+                pte_access |= ACC_EXEC_MASK;
+#if PTTYPE == 64
+                if (is_nx(vcpu))
+                        pte_access &= ~(pte >> PT64_NX_SHIFT);
+#endif
+                pte_access &= pt_access;
+
                 if (walker->level == PT_PAGE_TABLE_LEVEL) {
                         walker->gfn = gpte_to_gfn(pte);
                         break;
@@ -180,7 +189,7 @@ walk:
                         break;
                 }
 
-                walker->inherited_ar &= pte;
+                pt_access = pte_access;
                 --walker->level;
         }
 
@@ -197,7 +206,10 @@ walk:
         }
 
         walker->pte = pte;
-        pgprintk("%s: pte %llx\n", __FUNCTION__, (u64)pte);
+        walker->pt_access = pt_access;
+        walker->pte_access = pte_access;
+        pgprintk("%s: pte %llx pte_access %x pt_access %x\n",
+                 __FUNCTION__, (u64)pte, pt_access, pte_access);
         return 1;
 
 not_present:
@@ -218,7 +230,8 @@ err:
 }
 
 static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
-                           u64 *shadow_pte, u64 access_bits,
+                           u64 *shadow_pte, unsigned pt_access,
+                           unsigned pte_access,
                            int user_fault, int write_fault,
                            int *ptwrite, struct guest_walker *walker,
                            gfn_t gfn)
@@ -228,12 +241,11 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
         int was_rmapped = is_rmap_pte(*shadow_pte);
         struct page *page;
 
-        pgprintk("%s: spte %llx gpte %llx access %llx write_fault %d"
+        pgprintk("%s: spte %llx gpte %llx access %x write_fault %d"
                  " user_fault %d gfn %lx\n",
-                 __FUNCTION__, *shadow_pte, (u64)gpte, access_bits,
+                 __FUNCTION__, *shadow_pte, (u64)gpte, pt_access,
                  write_fault, user_fault, gfn);
 
-        access_bits &= gpte;
         /*
          * We don't set the accessed bit, since we sometimes want to see
          * whether the guest actually used the pte (in order to detect
@@ -242,12 +254,12 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
         spte = PT_PRESENT_MASK | PT_DIRTY_MASK;
         spte |= gpte & PT64_NX_MASK;
         if (!dirty)
-                access_bits &= ~PT_WRITABLE_MASK;
+                pte_access &= ~ACC_WRITE_MASK;
 
         page = gfn_to_page(vcpu->kvm, gfn);
 
         spte |= PT_PRESENT_MASK;
-        if (access_bits & PT_USER_MASK)
+        if (pte_access & ACC_USER_MASK)
                 spte |= PT_USER_MASK;
 
         if (is_error_page(page)) {
@@ -259,7 +271,7 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
 
         spte |= page_to_phys(page);
 
-        if ((access_bits & PT_WRITABLE_MASK)
+        if ((pte_access & ACC_WRITE_MASK)
             || (write_fault && !is_write_protection(vcpu) && !user_fault)) {
                 struct kvm_mmu_page *shadow;
 
@@ -273,7 +285,7 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
                 if (shadow) {
                         pgprintk("%s: found shadow page for %lx, marking ro\n",
                                  __FUNCTION__, gfn);
-                        access_bits &= ~PT_WRITABLE_MASK;
+                        pte_access &= ~ACC_WRITE_MASK;
                         if (is_writeble_pte(spte)) {
                                 spte &= ~PT_WRITABLE_MASK;
                                 kvm_x86_ops->tlb_flush(vcpu);
@@ -285,7 +297,7 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
 
 unshadowed:
 
-        if (access_bits & PT_WRITABLE_MASK)
+        if (pte_access & ACC_WRITE_MASK)
                 mark_page_dirty(vcpu->kvm, gfn);
 
         pgprintk("%s: setting spte %llx\n", __FUNCTION__, spte);
@@ -317,8 +329,8 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
         if (bytes < sizeof(pt_element_t))
                 return;
         pgprintk("%s: gpte %llx spte %p\n", __FUNCTION__, (u64)gpte, spte);
-        FNAME(set_pte)(vcpu, gpte, spte, PT_USER_MASK | PT_WRITABLE_MASK, 0,
-                       0, NULL, NULL, gpte_to_gfn(gpte));
+        FNAME(set_pte)(vcpu, gpte, spte, ACC_ALL, ACC_ALL,
+                       0, 0, NULL, NULL, gpte_to_gfn(gpte));
 }
 
 /*
@@ -331,6 +343,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
         hpa_t shadow_addr;
         int level;
         u64 *shadow_ent;
+        unsigned access = walker->pt_access;
 
         if (!is_present_pte(walker->pte))
                 return NULL;
@@ -349,7 +362,6 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                 u64 shadow_pte;
                 int metaphysical;
                 gfn_t table_gfn;
-                unsigned hugepage_access = 0;
 
                 shadow_ent = ((u64 *)__va(shadow_addr)) + index;
                 if (is_shadow_present_pte(*shadow_ent)) {
@@ -365,20 +377,15 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                 if (level - 1 == PT_PAGE_TABLE_LEVEL
                     && walker->level == PT_DIRECTORY_LEVEL) {
                         metaphysical = 1;
-                        hugepage_access = walker->pte;
-                        hugepage_access &= PT_USER_MASK | PT_WRITABLE_MASK;
                         if (!is_dirty_pte(walker->pte))
-                                hugepage_access &= ~PT_WRITABLE_MASK;
-                        hugepage_access >>= PT_WRITABLE_SHIFT;
-                        if (walker->pte & PT64_NX_MASK)
-                                hugepage_access |= (1 << 2);
+                                access &= ~ACC_WRITE_MASK;
                         table_gfn = gpte_to_gfn(walker->pte);
                 } else {
                         metaphysical = 0;
                         table_gfn = walker->table_gfn[level - 2];
                 }
                 shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
-                                               metaphysical, hugepage_access,
+                                               metaphysical, access,
                                                shadow_ent);
                 shadow_addr = __pa(shadow_page->spt);
                 shadow_pte = shadow_addr | PT_PRESENT_MASK | PT_ACCESSED_MASK
@@ -387,7 +394,8 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
         }
 
         FNAME(set_pte)(vcpu, walker->pte, shadow_ent,
-                       walker->inherited_ar, user_fault, write_fault,
+                       access, walker->pte_access & access,
+                       user_fault, write_fault,
                        ptwrite, walker, walker->gfn);
 
         return shadow_ent;