[PATCH 6.12.y 2/2] KVM: x86/mmu: Split kvm_mmu_zap_all_fast() into "front" and "back" halves

[Sasha Levin <sashal@kernel.org>]

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit b27622c4eeb125814081baaefe9175191be5b94d ]

Split kvm_mmu_zap_all_fast() into a "front half" and a "back half", where
the front half is everything that runs with mmu_lock held for write, and
the back half is the code that runs outside of mmu_lock.  This will allow
putting more code inside kvm_arch_flush_shadow_memslot()'s critical section
without having to take mmu_lock twice in quick succession.

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/20260709204948.1988414-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/mmu/mmu.c | 37 +++++++++++++++++++++++++------------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 8d46a307a2a3b..1c9d6132e24ad 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6489,20 +6489,11 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm)
 	kvm_mmu_commit_zap_page(kvm, &kvm->arch.zapped_obsolete_pages);
 }
 
-/*
- * Fast invalidate all shadow pages and use lock-break technique
- * to zap obsolete pages.
- *
- * It's required when memslot is being deleted or VM is being
- * destroyed, in these cases, we should ensure that KVM MMU does
- * not use any resource of the being-deleted slot or all slots
- * after calling the function.
- */
-static void kvm_mmu_zap_all_fast(struct kvm *kvm)
+static void __kvm_mmu_zap_all_fast_front_half(struct kvm *kvm)
 {
 	lockdep_assert_held(&kvm->slots_lock);
+	lockdep_assert_held_write(&kvm->mmu_lock);
 
-	write_lock(&kvm->mmu_lock);
 	trace_kvm_mmu_zap_all_fast(kvm);
 
 	/*
@@ -6534,8 +6525,12 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm)
 	kvm_make_all_cpus_request(kvm, KVM_REQ_MMU_FREE_OBSOLETE_ROOTS);
 
 	kvm_zap_obsolete_pages(kvm);
+}
 
-	write_unlock(&kvm->mmu_lock);
+static void __kvm_mmu_zap_all_fast_back_half(struct kvm *kvm)
+{
+	lockdep_assert_held(&kvm->slots_lock);
+	lockdep_assert_not_held(&kvm->mmu_lock);
 
 	/*
 	 * Zap the invalidated TDP MMU roots, all SPTEs must be dropped before
@@ -6554,6 +6549,24 @@ static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm)
 	return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages));
 }
 
+/*
+ * Fast invalidate all shadow pages and use lock-break technique
+ * to zap obsolete pages.
+ *
+ * It's required when memslot is being deleted or VM is being
+ * destroyed, in these cases, we should ensure that KVM MMU does
+ * not use any resource of the being-deleted slot or all slots
+ * after calling the function.
+ */
+static void kvm_mmu_zap_all_fast(struct kvm *kvm)
+{
+	write_lock(&kvm->mmu_lock);
+	__kvm_mmu_zap_all_fast_front_half(kvm);
+	write_unlock(&kvm->mmu_lock);
+
+	__kvm_mmu_zap_all_fast_back_half(kvm);
+}
+
 int kvm_mmu_init_vm(struct kvm *kvm)
 {
 	int r;
-- 
2.53.0