KVM: MMU: add SPTE_HOST_WRITEABLE flag to the shadow ptes

this flag notify that the host physical page we are pointing to from
the spte is write protected, and therefore we cant change its access
to be write unless we run get_user_pages(write = 1).

(this is needed for change_pte support in kvm)

Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index d2fec9c12d22..72558f8ff3f5 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -273,9 +273,13 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
         if (mmu_notifier_retry(vcpu, vcpu->arch.update_pte.mmu_seq))
                 return;
         kvm_get_pfn(pfn);
+        /*
+         * we call mmu_set_spte() with reset_host_protection = true beacuse that
+         * vcpu->arch.update_pte.pfn was fetched from get_user_pages(write = 1).
+         */
         mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
                      gpte & PT_DIRTY_MASK, NULL, PT_PAGE_TABLE_LEVEL,
-                     gpte_to_gfn(gpte), pfn, true);
+                     gpte_to_gfn(gpte), pfn, true, true);
 }
 
 /*
@@ -308,7 +312,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                                      user_fault, write_fault,
                                      gw->ptes[gw->level-1] & PT_DIRTY_MASK,
                                      ptwrite, level,
-                                     gw->gfn, pfn, false);
+                                     gw->gfn, pfn, false, true);
                         break;
                 }
 
@@ -558,6 +562,7 @@ static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
 static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 {
         int i, offset, nr_present;
+        bool reset_host_protection;
 
         offset = nr_present = 0;
 
@@ -595,9 +600,16 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 
                 nr_present++;
                 pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
+                if (!(sp->spt[i] & SPTE_HOST_WRITEABLE)) {
+                        pte_access &= ~ACC_WRITE_MASK;
+                        reset_host_protection = 0;
+                } else {
+                        reset_host_protection = 1;
+                }
                 set_spte(vcpu, &sp->spt[i], pte_access, 0, 0,
                          is_dirty_gpte(gpte), PT_PAGE_TABLE_LEVEL, gfn,
-                         spte_to_pfn(sp->spt[i]), true, false);
+                         spte_to_pfn(sp->spt[i]), true, false,
+                         reset_host_protection);
         }
 
         return !nr_present;