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Tue, 12 May 2026 13:35:46 -0700 (PDT) Received: from [192.168.10.48] ([176.206.106.181]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45ba2aaec3asm5293703f8f.15.2026.05.12.13.35.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 May 2026 13:35:46 -0700 (PDT) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: seanjc@google.com Subject: [PATCH v2] KVM: x86: use again the flush argument of __link_shadow_page() Date: Tue, 12 May 2026 22:35:45 +0200 Message-ID: <20260512203545.3031339-1-pbonzini@redhat.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Except in the case of parentless nested-TDP pages, mmu_page_zap_pte() clears the SPTE but leaves the invalid_list empty. In this case, using kvm_flush_remote_tlbs() as kvm_mmu_remote_flush_or_zap() does is overkill. Avoid flushing the entirety of the remote TLBs unless the invalid_list was populated: instead, use a more efficient gfn-targeting flush (if available) and skip it altogether if the caller guarantees that a TLB flush is not necessary. Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 892246204435..f0144ae8d891 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2526,6 +2526,23 @@ static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator) __shadow_walk_next(iterator, *iterator->sptep); } +/* + * Note: while normally KVM uses a "bool flush" return value to let + * the caller batch flushes, __link_shadow_page() flushes immediately + * before populating the parent PTE with the new shadow page. The + * typical callers, direct_map() and FNAME(fetch)(), are not going + * to zap more than one huge SPTE anyway. + * + * The only exception, where @flush can be false, is when a huge SPTE + * is replaced with a shadow page SPTE with a fully populated page table, + * which can happen from shadow_mmu_split_huge_page(). In this case, + * no memory is unmapped across the change to the page tables and no + * immediate flush is needed for correctness. + * + * Even in that case, calls to kvm_mmu_commit_zap_page() are not + * batched. Doing so would require adding an invalid_list argument + * all the way down to __walk_slot_rmaps(). + */ static void __link_shadow_page(struct kvm *kvm, struct kvm_mmu_memory_cache *cache, u64 *sptep, struct kvm_mmu_page *sp, bool flush) @@ -2541,8 +2558,10 @@ static void __link_shadow_page(struct kvm *kvm, parent_sp = sptep_to_sp(sptep); WARN_ON_ONCE(parent_sp->role.level == PG_LEVEL_4K); - mmu_page_zap_pte(kvm, parent_sp, sptep, &invalid_list); - kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, true); + if (mmu_page_zap_pte(kvm, parent_sp, sptep, &invalid_list)) + kvm_mmu_commit_zap_page(kvm, &invalid_list); + else if (flush) + kvm_flush_remote_tlbs_sptep(kvm, sptep); } spte = make_nonleaf_spte(sp->spt, sp_ad_disabled(sp)); -- 2.54.0