linux-kernel - [PATCH 27/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched

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Message-Id: <20211120045046.3940942-28-seanjc@google.com>
Date:   Sat, 20 Nov 2021 04:50:45 +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 27/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU
 in TDP MMU resched

When yielding in the TDP MMU iterator, service any pending TLB flush
before  dropping RCU protections in anticipation of using the callers RCU
"lock" as a proxy for vCPUs in the guest.

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

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 79a52717916c..55c16680b927 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -732,11 +732,11 @@ static inline bool tdp_mmu_iter_cond_resched(struct kvm *kvm,
 		return false;
 
 	if (need_resched() || rwlock_needbreak(&kvm->mmu_lock)) {
-		rcu_read_unlock();
-
 		if (flush)
 			kvm_flush_remote_tlbs(kvm);
 
+		rcu_read_unlock();
+
 		if (shared)
 			cond_resched_rwlock_read(&kvm->mmu_lock);
 		else
-- 
2.34.0.rc2.393.gf8c9666880-goog