linux-kernel - [PATCH v4 17/18] KVM: x86/tdp_mmu: Don't zap valid mirror roots in kvm_tdp_mmu_zap

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Message-Id: <20240718211230.1492011-18-rick.p.edgecombe@intel.com>
Date: Thu, 18 Jul 2024 14:12:29 -0700
From: Rick Edgecombe <rick.p.edgecombe@...el.com>
To: seanjc@...gle.com,
	pbonzini@...hat.com,
	kvm@...r.kernel.org
Cc: kai.huang@...el.com,
	dmatlack@...gle.com,
	erdemaktas@...gle.com,
	isaku.yamahata@...il.com,
	linux-kernel@...r.kernel.org,
	sagis@...gle.com,
	yan.y.zhao@...el.com,
	rick.p.edgecombe@...el.com
Subject: [PATCH v4 17/18] KVM: x86/tdp_mmu: Don't zap valid mirror roots in kvm_tdp_mmu_zap_all()

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.

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>
---
v4:
 - New patch
---
 arch/x86/kvm/mmu/tdp_mmu.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 2f3ba9d477e9..465c9fdb3301 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1044,19 +1044,23 @@ 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 roots, except valid mirror 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) and
+	 * they also won't be invalid until the VM is being torn down.
+	 *
+	 * 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.
 	 *
 	 * 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);
 }
 
-- 
2.34.1