KVM: MMU: Consolidate two guest pte reads in kvm_mmu_pte_write()

kvm_mmu_pte_write() reads guest ptes in two different occasions, both to
allow a 32-bit pae guest to update a pte with 4-byte writes.  Consolidate
these into a single read, which also allows us to consolidate another read
from an invlpg speculating a gpte into the shadow page table.

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

1 files changed, 31 insertions, 38 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 4455ddbe36f4..91f8b171c825 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2560,36 +2560,11 @@ static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu)
 }
 
 static void mmu_guess_page_from_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
-                                          const u8 *new, int bytes)
+                                          u64 gpte)
 {
         gfn_t gfn;
-        int r;
-        u64 gpte = 0;
         pfn_t pfn;
 
-        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_gpte(gpte))
                 return;
         gfn = (gpte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
@@ -2640,7 +2615,34 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
         int r;
 
         pgprintk("%s: gpa %llx bytes %d\n", __func__, gpa, bytes);
-        mmu_guess_page_from_pte_write(vcpu, gpa, new, bytes);
+
+        switch (bytes) {
+        case 4:
+                gentry = *(const u32 *)new;
+                break;
+        case 8:
+                gentry = *(const u64 *)new;
+                break;
+        default:
+                gentry = 0;
+                break;
+        }
+
+        /*
+         * 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) && bytes == 4) {
+                /* Handle a 32-bit guest writing two halves of a 64-bit gpte */
+                gpa &= ~(gpa_t)7;
+                r = kvm_read_guest(vcpu->kvm, gpa, &gentry, 8);
+                if (r)
+                        gentry = 0;
+        }
+
+        mmu_guess_page_from_pte_write(vcpu, gpa, gentry);
         spin_lock(&vcpu->kvm->mmu_lock);
         kvm_mmu_access_page(vcpu, gfn);
         kvm_mmu_free_some_pages(vcpu);
@@ -2705,20 +2707,11 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
                                 continue;
                 }
                 spte = &sp->spt[page_offset / sizeof(*spte)];
-                if ((gpa & (pte_size - 1)) || (bytes < pte_size)) {
-                        gentry = 0;
-                        r = kvm_read_guest_atomic(vcpu->kvm,
-                                                  gpa & ~(u64)(pte_size - 1),
-                                                  &gentry, pte_size);
-                        new = (const void *)&gentry;
-                        if (r < 0)
-                                new = NULL;
-                }
                 while (npte--) {
                         entry = *spte;
                         mmu_pte_write_zap_pte(vcpu, sp, spte);
-                        if (new)
-                                mmu_pte_write_new_pte(vcpu, sp, spte, new);
+                        if (gentry)
+                                mmu_pte_write_new_pte(vcpu, sp, spte, &gentry);
                         mmu_pte_write_flush_tlb(vcpu, entry, *spte);
                         ++spte;
                 }