KVM: x86/mmu: Return old SPTE from mmu_spte_clear_track_bits()

Return the old SPTE when clearing a SPTE and push the "old SPTE present"
check to the caller.  Private shadow page support will use the old SPTE
in rmap_remove() to determine whether or not there is a linked private
shadow page.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <b16bac1fd1357aaf39e425aab2177d3f89ee8318.1625186503.git.isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 85c7049..d9e3ac6 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -592,9 +592,9 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
  * Rules for using mmu_spte_clear_track_bits:
  * It sets the sptep from present to nonpresent, and track the
  * state bits, it is used to clear the last level sptep.
- * Returns non-zero if the PTE was previously valid.
+ * Returns the old PTE.
  */
-static int mmu_spte_clear_track_bits(u64 *sptep)
+static u64 mmu_spte_clear_track_bits(u64 *sptep)
 {
        kvm_pfn_t pfn;
        u64 old_spte = *sptep;
@@ -605,7 +605,7 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
                old_spte = __update_clear_spte_slow(sptep, 0ull);
 
        if (!is_shadow_present_pte(old_spte))
-               return 0;
+               return old_spte;
 
        pfn = spte_to_pfn(old_spte);
 
@@ -622,7 +622,7 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
        if (is_dirty_spte(old_spte))
                kvm_set_pfn_dirty(pfn);
 
-       return 1;
+       return old_spte;
 }
 
 /*
@@ -1119,7 +1119,9 @@ out:
 
 static void drop_spte(struct kvm *kvm, u64 *sptep)
 {
-       if (mmu_spte_clear_track_bits(sptep))
+       u64 old_spte = mmu_spte_clear_track_bits(sptep);
+
+       if (is_shadow_present_pte(old_spte))
                rmap_remove(kvm, sptep);
 }