From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4F094606D804 for ; Wed, 4 Nov 2026 18:06:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=rzdsitwB; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=TRjh1EW7 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Unsubscribe-Post:List-Owner; bh=BKcs+4/yEuxVnS2VouqR2WzhlLvVEKGo4vjTDXvNfG0=; b=rzdsitwBC/m8i9zZM6hCnWXGBx NQex0d+V9uHfZ3JIHaJmqoV0h9wjMM4BNBAaJkJ02Kc2B80xToRzMIAe/DG991tQ/EY19Y3yN7QfU Cci4yY8656lUWrJj+T/5qDafrZlnW1Jbj36YaiVtkLMrf2eMoPo7b9HATkWXTti0GBLG/11G63t8x GbDtT7HaF9Xib74nG/46c1UpGeE5LOKg6yhI3sL+wvoO2u4Ns738dYaFH0L6pnB5dbamuDm9WgPw/ j5avsZ2HUv7h4RvMLmptFYNiQbmlBSJazP3NtI2jyyxD8o4F+cc7eWsITe6jmkkrO/BVuGsPUf4ix yjeoTDfw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xOfNM-00000006Llx-32jv; Wed, 04 Nov 2026 18:06:20 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xOfNL-00000006Llk-3P3s for linux-arm-kernel@lists.infradead.org; Wed, 04 Nov 2026 18:06:19 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 0AA404393F; Wed, 4 Nov 2026 18:06:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 599191F000C1; Wed, 4 Nov 2026 18:06:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793815578; bh=BKcs+4/yEuxVnS2VouqR2WzhlLvVEKGo4vjTDXvNfG0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=TRjh1EW7SELcNJfvo8muQIl89zA8WNp5y+E/1UNt7WjdfWpTr2l0YsLmXukzDVdcb MtN2Cul5ftUHPOTHRrWXZz15d4519+/JX99BQ9EFBwDMa6Z/p/gA/7JD6TVOjZ/vBi OB2BFXWBdTOLqM3i58cTC7RkkGMn7JN3bmprsMKqcRE4sWc3gaCR5ux18JUu+f9BiO BCPYty2It/rmH4QXelFrEbogHGZF8Vt5TPltvlSpfWz7CqHpOWk6+r1T5T2x9a+Mth pJ5gQEHLZXIi9vb1beXsTVGfz4uej5iLeuj8/pO+5HwMB3yX/Yju+Mj/kKNoIeWGj2 9/KBA+HcaF4xA== Date: Wed, 4 Nov 2026 18:06:12 +0000 From: "Lorenzo Stoakes (ARM)" To: Sean Christopherson Cc: Alexandru Elisei , pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org, oupton@kernel.org, suzuki.poulose@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, david@kernel.org, mark.rutland@arm.com, ackerleytng@google.com Subject: Re: [PATCH v2] KVM: Ignore MMU notifiers for guest_memfd-only memslots Message-ID: References: <20260714160411.302386-1-alexandru.elisei@arm.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" X-Spam-Status: No, score=-10.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 [updated David's email address to @kernel.org] On Wed, Aug 12, 2026 at 10:42:50AM +0100, Alexandru Elisei wrote: [ ... ] > On Fri, Jul 24, 2026 at 12:52:20PM -0700, Sean Christopherson wrote: > > It'll probably take me a few weeks to circle back to this, as I finally crawled > > out from underneath a pile of urgent and am just now getting back into review > > mode, but this is fairly high on my todo list, so with luck we might still squeeze > > this into 7.3. Hey Sean, I wondered whether you'd had a chance to look at this? After discussing this with Marc and Alex it is clear that this is really a blocker for Alex's SPE series, as we need a sensible means of ensuring that stage-2 mappings stay in place. So ideally would prefer to get something like this in in the next cycle, if you don't have any objections to it? :) If it'd be easier, I think a smaller version of the same patch would also give us what we need? I.e. your snippet from June with the page ageing part dropped, as below. Thanks! diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index e7fc94e2910a..a6f37bdb0902 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -264,6 +264,7 @@ union kvm_mmu_notifier_arg { enum kvm_gfn_range_filter { KVM_FILTER_SHARED = BIT(0), KVM_FILTER_PRIVATE = BIT(1), + KVM_FILTER_USERSPACE_MAPPINGS = BIT(2), }; struct kvm_gfn_range { diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index cf4cb586f140..6fc3b443c305 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -616,8 +616,13 @@ static __always_inline kvm_mn_ret_t kvm_handle_hva_range(struct kvm *kvm, /* * HVA-based notifications aren't relevant to private * mappings as they don't have a userspace mapping. + * + * Memslots where guest_memfd is the only memory + * provider can also safely ignore changes to the + * userspace mapping. */ - gfn_range.attr_filter = KVM_FILTER_SHARED; + gfn_range.attr_filter = KVM_FILTER_SHARED | + KVM_FILTER_USERSPACE_MAPPINGS; /* * {gfn(page) | page intersects with [hva_start, hva_end)} = @@ -724,6 +729,17 @@ void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end) bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range) { kvm_mmu_invalidate_range_add(kvm, range->start, range->end); + + /* + * When reacting to changes in userspace mappings, don't unmap memslots + * that are guest_memfd-only, in which case KVM's MMU mappings are + * pulled directly from guest_memfd, i.e. don't depend on the userspace + * mappings. + */ + if (range->attr_filter & KVM_FILTER_USERSPACE_MAPPINGS && + kvm_memslot_is_gmem_only(range->slot)) + return false; + return kvm_unmap_gfn_range(kvm, range); } -- Cheers, Lorenzo