[PATCH 7.1.y 7/8] KVM: x86/mmu: Use split "zap all fast" helpers when invalidating memslot

[Sasha Levin <sashal@kernel.org>]

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit db095727ff5739f4f46ee641ee6ef450032886db ]

Manually invoke the front half and back half of the "zap all fast" flow
when invalidating a memslot so that mmu_lock is acquired at function scope
in kvm_arch_flush_shadow_memslot().   This will allow putting more code
inside the critical section without having to take mmu_lock twice in quick
succession.

Opportunistically open code checking whether or not to do the fast zap, to
discourage removing the local "zap_all" in a future cleanup, i.e. to ensure
the SLOT_ZAP_ALL quirk is queried exactly once.  Processing the front half
but not the back half of the fast zap (if SLOT_ZAP_ALL were disabled
concurrently) would result in KVM unnecessarily keeping invalid TDP MMU
roots until the VM is destroyed.

No functional change intended.

Cc: stable@vger.kernel.org # 6.12.x
Reviewed-by: Michael Roth <michael.roth@amd.com>
Link: https://patch.msgid.link/20260709204948.1988414-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Stable-dep-of: d1a3c2162334 ("KVM: SEV: Forcefully invalidate SNP VMSA if its backing gmem page is zapped")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/mmu/mmu.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 10c28f78bf276..43fadc53a1b92 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7454,12 +7454,6 @@ static void kvm_mmu_zap_memslot_pages_and_flush(struct kvm *kvm,
 	kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, flush);
 }
 
-static inline bool kvm_memslot_flush_zap_all(struct kvm *kvm)
-{
-	return kvm->arch.vm_type == KVM_X86_DEFAULT_VM &&
-	       kvm_check_has_quirk(kvm, KVM_X86_QUIRK_SLOT_ZAP_ALL);
-}
-
 void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
 				   struct kvm_memory_slot *slot)
 {
@@ -7470,16 +7464,23 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
 		.may_block = true,
 		.attr_filter = KVM_FILTER_PRIVATE | KVM_FILTER_SHARED,
 	};
+	bool zap_all = kvm->arch.vm_type == KVM_X86_DEFAULT_VM &&
+		       kvm_check_has_quirk(kvm, KVM_X86_QUIRK_SLOT_ZAP_ALL);
 	bool flush;
 
-	if (kvm_memslot_flush_zap_all(kvm)) {
-		kvm_mmu_zap_all_fast(kvm);
+	write_lock(&kvm->mmu_lock);
+
+	if (zap_all) {
+		__kvm_mmu_zap_all_fast_front_half(kvm);
 	} else {
-		write_lock(&kvm->mmu_lock);
 		flush = kvm_unmap_gfn_range(kvm, &range);
 		kvm_mmu_zap_memslot_pages_and_flush(kvm, slot, flush);
-		write_unlock(&kvm->mmu_lock);
 	}
+
+	write_unlock(&kvm->mmu_lock);
+
+	if (zap_all)
+		__kvm_mmu_zap_all_fast_back_half(kvm);
 }
 
 void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen)
-- 
2.53.0