From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793815579; b=YIn6GXn+25F4uGKEl9QNVOn+FPKJrqwzf3g9yj9xC+tU6+vKGKLf0B/xw3P0O37DlXAx 5VKnOKLU2jFV/CdHtAhxaswdGVoaxWtH8aW4FXHh3mTKP+mGspC1YHvlgAceEdRkrpLuO pgMzD+Yh7NsYGJ4ynYnJAa/8SXoiK1/w8Aku9+i4hZYokZCx06hoEkG/C4hOrEnjdfZ9e FJzzePUxi/QpZaQ8aJzKBO1Z/CiBvEPYXglm+YHMoD3pNd+6xFmlbgTqaL6yROiyyf0fj Wty838JPLQ5sb73PJqWYMqV6RUC50tXGkPuPO/kjOe9zz5swQJ3u9cJwkhVnv/5J7Ug== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793815579; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=BKcs+4/yEuxVnS2VouqR2WzhlLvVEKGo4vjTDXvNfG0=; b=1vstN06z/PRaCKPDkTmmyeiJDRdYtduKLZkoiCnarFS/z5hHi00ac2rCh+dt8R4dqHM/ qQ+yWXVIgICAmKS59hmnl6kMCH+8dPevdF/+N6cQrBj1NhaQkwhreyZsmzYN0Qn2zdb3R hppT/8GBDEsMdVXSU/h/uscBME83XdK5D3F/NkneHrOU7kYohfQhcCluHIARE/LATFOSI 2A21nBOS9J4mn7Zg2bH3qK+goTpFi4+BWdFgvZQUfFDlcJJOdjsnbqVeI6Zd+VE3nO6Dz i5rg2jSCiuluZvjYcROPbbrBizAqGDZJ6v3fID9Z7wmLnd0bk/HlVC8wTC+zz6kNOSg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=TRjh1EW7; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 189A2606A328; Wed, 4 Nov 2026 18:06:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=TRjh1EW7 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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: [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