linux-kernel - [PATCH v6 17/18] KVM: x86/tdp_mmu: Don't zap valid mirror roots in kvm_tdp_mmu_zap

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Message-ID: <20241222193445.349800-18-pbonzini@redhat.com>
Date: Sun, 22 Dec 2024 14:34:44 -0500
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: yan.y.zhao@...el.com,
	isaku.yamahata@...el.com,
	binbin.wu@...ux.intel.com,
	rick.p.edgecombe@...el.com
Subject: [PATCH v6 17/18] KVM: x86/tdp_mmu: Don't zap valid mirror roots in kvm_tdp_mmu_zap_all()

From: Rick Edgecombe <rick.p.edgecombe@...el.com>

Don't zap valid mirror roots in kvm_tdp_mmu_zap_all(), which in effect
is only direct roots (invalid and valid).

For TDX, kvm_tdp_mmu_zap_all() is only called during MMU notifier
release. Since, mirrored EPT comes from guest mem, it will never be
mapped to userspace, and won't apply. But in addition to be unnecessary,
mirrored EPT is cleaned up in a special way during VM destruction.

Pass the KVM_INVALID_ROOTS bit into __for_each_tdp_mmu_root_yield_safe()
as well, to clean up invalid direct roots, as is the current behavior.

While at it, remove an obsolete reference to work item-based zapping.

Co-developed-by: Yan Zhao <yan.y.zhao@...el.com>
Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Message-ID: <20240718211230.1492011-18-rick.p.edgecombe@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index ca2b95b75ca4..046b6ba31197 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -999,19 +999,21 @@ void kvm_tdp_mmu_zap_all(struct kvm *kvm)
 	struct kvm_mmu_page *root;
 
 	/*
-	 * Zap all roots, including invalid roots, as all SPTEs must be dropped
-	 * before returning to the caller.  Zap directly even if the root is
-	 * also being zapped by a worker.  Walking zapped top-level SPTEs isn't
-	 * all that expensive and mmu_lock is already held, which means the
-	 * worker has yielded, i.e. flushing the work instead of zapping here
-	 * isn't guaranteed to be any faster.
+	 * Zap all direct roots, including invalid direct roots, as all direct
+	 * SPTEs must be dropped before returning to the caller. For TDX, mirror
+	 * roots don't need handling in response to the mmu notifier (the caller).
+	 *
+	 * Zap directly even if the root is also being zapped by a concurrent
+	 * "fast zap".  Walking zapped top-level SPTEs isn't all that expensive
+	 * and mmu_lock is already held, which means the other thread has yielded.
 	 *
 	 * A TLB flush is unnecessary, KVM zaps everything if and only the VM
 	 * is being destroyed or the userspace VMM has exited.  In both cases,
 	 * KVM_RUN is unreachable, i.e. no vCPUs will ever service the request.
 	 */
 	lockdep_assert_held_write(&kvm->mmu_lock);
-	for_each_tdp_mmu_root_yield_safe(kvm, root)
+	__for_each_tdp_mmu_root_yield_safe(kvm, root, -1,
+					   KVM_DIRECT_ROOTS | KVM_INVALID_ROOTS)
 		tdp_mmu_zap_root(kvm, root, false);
 }
 
-- 
2.43.5