linux-kernel - [RFC PATCH 6/9] KVM: x86/mmu: Process only valid TDP MMU roots when aging a gfn range

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Message-ID: <20240801183453.57199-7-seanjc@google.com>
Date: Thu,  1 Aug 2024 11:34:50 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 6/9] KVM: x86/mmu: Process only valid TDP MMU roots when
 aging a gfn range

Skip invalid TDP MMU roots when aging a gfn range.  There is zero reason
to process invalid roots, as they by definition hold stale information.
E.g. if a root is invalid because its from a previous memslot generation,
in the unlikely event the root has a SPTE for the gfn, then odds are good
that the gfn=>hva mapping is different, i.e. doesn't map to the hva that
is being aged by the primary MMU.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 2b0fc601d2ce..b358642890e1 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1202,9 +1202,11 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
 
 	/*
 	 * Don't support rescheduling, none of the MMU notifiers that funnel
-	 * into this helper allow blocking; it'd be dead, wasteful code.
+	 * into this helper allow blocking; it'd be dead, wasteful code.  Note,
+	 * this helper must NOT be used to unmap GFNs, as it processes only
+	 * valid roots!
 	 */
-	for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
+	for_each_valid_tdp_mmu_root(kvm, root, range->slot->as_id) {
 		rcu_read_lock();
 
 		tdp_root_for_each_leaf_pte(iter, root, range->start, range->end)
-- 
2.46.0.rc1.232.g9752f9e123-goog