[PATCH 16/28] KVM: x86/mmu: WARN if old _or_ new SPTE is REMOVED in non-atomic path

Sean Christopherson
2021-11-20T04:52:49Z

WARN if the new_spte being set by __tdp_mmu_set_spte() is a REMOVED_SPTE,
which is called out by the comment as being disallowed but not actually
checked. Keep the WARN on the old_spte as well, because overwriting a
REMOVED_SPTE in the non-atomic path is also disallowed (as evidence by
lack of splats with the existing WARN).

Fixes: 08f07c800e9d ("KVM: x86/mmu: Flush TLBs after zap in TDP MMU PF handler")
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/tdp_mmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 085f6b09e5f3..d9524b387221 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -638,13 +638,13 @@ static inline void __tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
lockdep_assert_held_write(&kvm->mmu_lock);

/*
- * No thread should be using this function to set SPTEs to the
+ * No thread should be using this function to set SPTEs to or from the
* temporary removed SPTE value.
* If operating under the MMU lock in read mode, tdp_mmu_set_spte_atomic
* should be used. If operating under the MMU lock in write mode, the
* use of the removed SPTE should not be necessary.
*/
- WARN_ON(is_removed_spte(iter->old_spte));
+ WARN_ON(is_removed_spte(iter->old_spte) || is_removed_spte(new_spte));

kvm_tdp_mmu_write_spte(iter->sptep, new_spte);

--
2.34.0.rc2.393.gf8c9666880-goog