linux-kernel - [RFC PATCH 1/8] KVM: x86/mmu: Return old SPTE from mmu_spte_clear_track

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Date:   Fri, 31 Jul 2020 14:23:16 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        eric van tassell <Eric.VanTassell@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [RFC PATCH 1/8] 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.  Tracking pinned SPTEs will use the old SPTE
in rmap_remove() to determine whether or not the SPTE is pinned.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/mmu/mmu.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 289dddff2615f..d737042fea55e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -930,9 +930,9 @@ 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;
@@ -943,7 +943,7 @@ 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);
 
@@ -960,7 +960,7 @@ 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;
 }
 
 /*
@@ -1484,7 +1484,9 @@ static u64 *rmap_get_next(struct rmap_iterator *iter)
 
 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);
 }
 
-- 
2.28.0