KVM: MMU: Use ptep_user for cmpxchg_gpte()

The address of the gpte was already calculated and stored in ptep_user
before entering cmpxchg_gpte().

This patch makes cmpxchg_gpte() to use that to make it clear that we
are using the same address during walk_addr_generic().

Note that the unlikely annotations are used to show that the conditions
are something unusual rather than for performance.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 12 insertions, 14 deletions

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index e3f81418797e..6c4dc010c4cb 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -79,21 +79,19 @@ static gfn_t gpte_to_gfn_lvl(pt_element_t gpte, int lvl)
 }
 
 static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
-                         gfn_t table_gfn, unsigned index,
-                         pt_element_t orig_pte, pt_element_t new_pte)
+                               pt_element_t __user *ptep_user, unsigned index,
+                               pt_element_t orig_pte, pt_element_t new_pte)
 {
+        int npages;
         pt_element_t ret;
         pt_element_t *table;
         struct page *page;
-        gpa_t gpa;
 
-        gpa = mmu->translate_gpa(vcpu, table_gfn << PAGE_SHIFT,
-                                 PFERR_USER_MASK|PFERR_WRITE_MASK);
-        if (gpa == UNMAPPED_GVA)
+        npages = get_user_pages_fast((unsigned long)ptep_user, 1, 1, &page);
+        /* Check if the user is doing something meaningless. */
+        if (unlikely(npages != 1))
                 return -EFAULT;
 
-        page = gfn_to_page(vcpu->kvm, gpa_to_gfn(gpa));
-
         table = kmap_atomic(page, KM_USER0);
         ret = CMPXCHG(&table[index], orig_pte, new_pte);
         kunmap_atomic(table, KM_USER0);
@@ -220,9 +218,9 @@ walk:
                         int ret;
                         trace_kvm_mmu_set_accessed_bit(table_gfn, index,
                                                        sizeof(pte));
-                        ret = FNAME(cmpxchg_gpte)(vcpu, mmu, table_gfn,
-                                        index, pte, pte|PT_ACCESSED_MASK);
-                        if (ret < 0) {
+                        ret = FNAME(cmpxchg_gpte)(vcpu, mmu, ptep_user, index,
+                                                  pte, pte|PT_ACCESSED_MASK);
+                        if (unlikely(ret < 0)) {
                                 present = false;
                                 break;
                         } else if (ret)
@@ -279,9 +277,9 @@ walk:
                 int ret;
 
                 trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
-                ret = FNAME(cmpxchg_gpte)(vcpu, mmu, table_gfn, index, pte,
-                            pte|PT_DIRTY_MASK);
-                if (ret < 0) {
+                ret = FNAME(cmpxchg_gpte)(vcpu, mmu, ptep_user, index,
+                                          pte, pte|PT_DIRTY_MASK);
+                if (unlikely(ret < 0)) {
                         present = false;
                         goto error;
                 } else if (ret)