linux-kernel - [PATCH] KVM: x86/mmu: Skip MMIO SPTE invalidation if enable_mmio

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Message-ID: <20250926135139.1597781-1-dmaluka@chromium.org>
Date: Fri, 26 Sep 2025 15:51:39 +0200
From: Dmytro Maluka <dmaluka@...omium.org>
To: kvm@...r.kernel.org,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org,
	Grzegorz Jaszczyk <jaszczyk@...gle.com>,
	Vineeth Pillai <vineethrp@...gle.com>,
	Tomasz Nowicki <tnowicki@...gle.com>,
	Chuanxiao Dong <chuanxiao.dong@...el.com>,
	Dmytro Maluka <dmaluka@...omium.org>
Subject: [PATCH] KVM: x86/mmu: Skip MMIO SPTE invalidation if enable_mmio_caching=0

If MMIO caching is disabled, there are no MMIO SPTEs to invalidate, so
the costly zapping of all pages is unnecessary even in the unlikely case
when the MMIO generation number has wrapped.

Signed-off-by: Dmytro Maluka <dmaluka@...omium.org>
---
 arch/x86/kvm/mmu/mmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6e838cb6c9e1..bad613e8fa95 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7339,6 +7339,9 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen)
 {
 	WARN_ON_ONCE(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS);
 
+	if (!enable_mmio_caching)
+		return;
+
 	gen &= MMIO_SPTE_GEN_MASK;
 
 	/*
-- 
2.51.0.536.g15c5d4f767-goog