KVM: MMU: Optimize is_last_gpte()

Instead of branchy code depending on level, gpte.ps, and mmu configuration,
prepare everything in a bitmap during mode changes and look it up during
runtime.

Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

4 files changed, 41 insertions, 20 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3318bde206a5..43aeb9422839 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -298,6 +298,13 @@ struct kvm_mmu {
         u64 *lm_root;
         u64 rsvd_bits_mask[2][4];
 
+        /*
+         * Bitmap: bit set = last pte in walk
+         * index[0:1]: level (zero-based)
+         * index[2]: pte.ps
+         */
+        u8 last_pte_bitmap;
+
         bool nx;
 
         u64 pdptrs[4]; /* pae */
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9c6188931f87..d289fee1ffb8 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3447,6 +3447,15 @@ static inline unsigned gpte_access(struct kvm_vcpu *vcpu, u64 gpte)
         return access;
 }
 
+static inline bool is_last_gpte(struct kvm_mmu *mmu, unsigned level, unsigned gpte)
+{
+        unsigned index;
+
+        index = level - 1;
+        index |= (gpte & PT_PAGE_SIZE_MASK) >> (PT_PAGE_SIZE_SHIFT - 2);
+        return mmu->last_pte_bitmap & (1 << index);
+}
+
 #define PTTYPE 64
 #include "paging_tmpl.h"
 #undef PTTYPE
@@ -3548,6 +3557,24 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu
         }
 }
 
+static void update_last_pte_bitmap(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
+{
+        u8 map;
+        unsigned level, root_level = mmu->root_level;
+        const unsigned ps_set_index = 1 << 2;  /* bit 2 of index: ps */
+
+        if (root_level == PT32E_ROOT_LEVEL)
+                --root_level;
+        /* PT_PAGE_TABLE_LEVEL always terminates */
+        map = 1 | (1 << ps_set_index);
+        for (level = PT_DIRECTORY_LEVEL; level <= root_level; ++level) {
+                if (level <= PT_PDPE_LEVEL
+                    && (mmu->root_level >= PT32E_ROOT_LEVEL || is_pse(vcpu)))
+                        map |= 1 << (ps_set_index | (level - 1));
+        }
+        mmu->last_pte_bitmap = map;
+}
+
 static int paging64_init_context_common(struct kvm_vcpu *vcpu,
                                         struct kvm_mmu *context,
                                         int level)
@@ -3557,6 +3584,7 @@ static int paging64_init_context_common(struct kvm_vcpu *vcpu,
 
         reset_rsvds_bits_mask(vcpu, context);
         update_permission_bitmask(vcpu, context);
+        update_last_pte_bitmap(vcpu, context);
 
         ASSERT(is_pae(vcpu));
         context->new_cr3 = paging_new_cr3;
@@ -3586,6 +3614,7 @@ static int paging32_init_context(struct kvm_vcpu *vcpu,
 
         reset_rsvds_bits_mask(vcpu, context);
         update_permission_bitmask(vcpu, context);
+        update_last_pte_bitmap(vcpu, context);
 
         context->new_cr3 = paging_new_cr3;
         context->page_fault = paging32_page_fault;
@@ -3647,6 +3676,7 @@ static int init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
         }
 
         update_permission_bitmask(vcpu, context);
+        update_last_pte_bitmap(vcpu, context);
 
         return 0;
 }
@@ -3724,6 +3754,7 @@ static int init_kvm_nested_mmu(struct kvm_vcpu *vcpu)
         }
 
         update_permission_bitmask(vcpu, g_context);
+        update_last_pte_bitmap(vcpu, g_context);
 
         return 0;
 }
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 584660775d08..69871080e866 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -20,7 +20,8 @@
 #define PT_ACCESSED_MASK (1ULL << PT_ACCESSED_SHIFT)
 #define PT_DIRTY_SHIFT 6
 #define PT_DIRTY_MASK (1ULL << PT_DIRTY_SHIFT)
-#define PT_PAGE_SIZE_MASK (1ULL << 7)
+#define PT_PAGE_SIZE_SHIFT 7
+#define PT_PAGE_SIZE_MASK (1ULL << PT_PAGE_SIZE_SHIFT)
 #define PT_PAT_MASK (1ULL << 7)
 #define PT_GLOBAL_MASK (1ULL << 8)
 #define PT64_NX_SHIFT 63
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 1b4c14d235a0..134ea7b1c585 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -103,24 +103,6 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
         return (ret != orig_pte);
 }
 
-static bool FNAME(is_last_gpte)(struct guest_walker *walker,
-                                struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
-                                pt_element_t gpte)
-{
-        if (walker->level == PT_PAGE_TABLE_LEVEL)
-                return true;
-
-        if ((walker->level == PT_DIRECTORY_LEVEL) && is_large_pte(gpte) &&
-            (PTTYPE == 64 || is_pse(vcpu)))
-                return true;
-
-        if ((walker->level == PT_PDPE_LEVEL) && is_large_pte(gpte) &&
-            (mmu->root_level == PT64_ROOT_LEVEL))
-                return true;
-
-        return false;
-}
-
 static int FNAME(update_accessed_dirty_bits)(struct kvm_vcpu *vcpu,
                                              struct kvm_mmu *mmu,
                                              struct guest_walker *walker,
@@ -247,7 +229,7 @@ retry_walk:
                 pte_access = pt_access & gpte_access(vcpu, pte);
 
                 walker->ptes[walker->level - 1] = pte;
-        } while (!FNAME(is_last_gpte)(walker, vcpu, mmu, pte));
+        } while (!is_last_gpte(mmu, walker->level, pte));
 
         eperm |= permission_fault(mmu, pte_access, access);
         if (unlikely(eperm)) {