[PATCH v2 10/15] KVM: x86/mmu: Drop KVM_BUG_ON() on shared lock to zap child external PTEs

[Yan Zhao]

From: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>

Drop the KVM_BUG_ON() in the KVM MMU core before zapping child external
PTEs, since requiring zapping PTEs to be protected by exclusive mmu_lock is
TDX's specific requirement.

No need to plumb the shared/exclusive info into the remove_external_spte()
op or move the KVM_BUG_ON() to TDX, because
- There's already an assertion of exclusive mmu_lock protection in TDX.
- The KVM_BUG_ON() is a bit redundant given that if there's any bug causing
  zapping of leaf PTEs in S-EPT under shared mmu_lock, SEAMCALL failures
  due to contention would result in TDX_BUG_ON() in TDX.

Link: https://lore.kernel.org/kvm/aYUarHf3KEwHGuJe@xxxxxxxxxx/
Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
---
MMU_refactors v2:
- Updated commit log and title. (Yan)
---
 arch/x86/kvm/mmu/tdp_mmu.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index ada4a0837298..553a30628960 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -473,10 +473,8 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared)
 		}
 		handle_changed_spte(kvm, sp, gfn, old_spte, FROZEN_SPTE, level, shared);
 
-		if (is_mirror_sp(sp)) {
-			KVM_BUG_ON(shared, kvm);
+		if (is_mirror_sp(sp))
 			remove_external_spte(kvm, gfn, old_spte, level);
-		}
 	}
 
 	if (is_mirror_sp(sp) &&
-- 
2.43.2