linux-kernel - [PATCH 12/28] KVM: x86/mmu: Batch TLB flushes from TDP MMU for MMU notifier change

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Message-Id: <20211120045046.3940942-13-seanjc@google.com>
Date:   Sat, 20 Nov 2021 04:50:30 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Hou Wenlong <houwenlong93@...ux.alibaba.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 12/28] KVM: x86/mmu: Batch TLB flushes from TDP MMU for MMU
 notifier change_spte

Batch TLB flushes (with other MMUs) when handling ->change_spte()
notifications in the TDP MMU.  The MMU notifier path in question doesn't
allow yielding and correcty flushes before dropping mmu_lock.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 8e446ef03022..06b500fab248 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1182,13 +1182,12 @@ static bool set_spte_gfn(struct kvm *kvm, struct tdp_iter *iter,
  */
 bool kvm_tdp_mmu_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	bool flush = kvm_tdp_mmu_handle_gfn(kvm, range, set_spte_gfn);
-
-	/* FIXME: return 'flush' instead of flushing here. */
-	if (flush)
-		kvm_flush_remote_tlbs_with_address(kvm, range->start, 1);
-
-	return false;
+	/*
+	 * No need to handle the remote TLB flush under RCU protection, the
+	 * target SPTE _must_ be a leaf SPTE, i.e. cannot result in freeing a
+	 * shadow page.  See the WARN on pfn_changed in __handle_changed_spte().
+	 */
+	return kvm_tdp_mmu_handle_gfn(kvm, range, set_spte_gfn);
 }
 
 /*
-- 
2.34.0.rc2.393.gf8c9666880-goog