From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4619D149C68; Mon, 5 Aug 2024 07:57:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722844651; cv=none; b=qvigliiJ9beQjhqRpbYq9Qgp4ogpu9AuZjRKLBM9/kGhB172/WfQRVY1QCdw4cxUBai/DEpJ202nYqX+W3okxd41Oa6Mn1RWuUG9LUd4nhsmQBCGhP9iYyQfVD/UVS/4wPckXAnk6qnNEqo/p1H7DUWTTSZev9lcxDwB2LrN3NA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722844651; c=relaxed/simple; bh=Geket5xHj+rV/lTGgYhI+mobx7QxgrRmSJGYSEDRkpk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=Y54TeAirpMelSVU1oSi7HNK07/FqLHF4NUTPp4bVQqznk/EcKOsJIEik67eN55jdGyz6kxvKNFxSzkuiQnhTmHGx6GI43/YjcQroiVBrrH/PnKH+PaesdBpe/cH7hRt8zxGu+/iJQn9RTdZ4k3sbGxULkGODVvkg0UQmmwncCow= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UBQwR8Dv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UBQwR8Dv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 59266C32782; Mon, 5 Aug 2024 07:57:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722844650; bh=Geket5xHj+rV/lTGgYhI+mobx7QxgrRmSJGYSEDRkpk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=UBQwR8Dv5k7JtkeG4laWC2Xs0oOnozRLy+3hVYnDYQn2Ed5eCrDNKiqSjdoXT4acx 1hPdTL4JDstUhQJJ7lCM7YYqnV4Qh1m6C+CK460q8siGoQwJJKzkWsjMOX4qcfmelz A6Yt57Xlk92ABmDDhigDShW3vM0pnXKBZJdZWOrnwttmRyqlw3hP4oeUm/b5LanIcX fVlLRwpf9c9nuW6b7SobjiC6lu0VN8iuGUvVZHCooHxsAnFt7ePn4zwuEV1kg+BLX4 tQQRPbEFjC/HMt7oQ6FPHcOxgz1D3ofgxyEIT69W/KjqEASCYIB1LwhYcesfg0NZf1 asOwN60f4YLIQ== X-Mailer: emacs 31.0.50 (via feedmail 11-beta-1 I) From: Aneesh Kumar K.V To: Sean Christopherson Cc: Paolo Bonzini , Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , David Stevens Subject: Re: [PATCH v12 02/84] KVM: arm64: Disallow copying MTE to guest memory while KVM is dirty logging In-Reply-To: References: <20240726235234.228822-1-seanjc@google.com> <20240726235234.228822-3-seanjc@google.com> Date: Mon, 05 Aug 2024 13:27:18 +0530 Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Sean Christopherson writes: > On Thu, Aug 01, 2024, Aneesh Kumar K.V wrote: >> Sean Christopherson writes: >> >> > Disallow copying MTE tags to guest memory while KVM is dirty logging, as >> > writing guest memory without marking the gfn as dirty in the memslot could >> > result in userspace failing to migrate the updated page. Ideally (maybe?), >> > KVM would simply mark the gfn as dirty, but there is no vCPU to work with, >> > and presumably the only use case for copy MTE tags _to_ the guest is when >> > restoring state on the target. >> > >> > Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest") >> > Signed-off-by: Sean Christopherson >> > --- >> > arch/arm64/kvm/guest.c | 5 +++++ >> > 1 file changed, 5 insertions(+) >> > >> > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c >> > index e1f0ff08836a..962f985977c2 100644 >> > --- a/arch/arm64/kvm/guest.c >> > +++ b/arch/arm64/kvm/guest.c >> > @@ -1045,6 +1045,11 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >> > >> > mutex_lock(&kvm->slots_lock); >> > >> > + if (write && atomic_read(&kvm->nr_memslots_dirty_logging)) { >> > + ret = -EBUSY; >> > + goto out; >> > + } >> > + >> > >> >> is this equivalent to kvm_follow_pfn() with kfp->pin = 1 ? > > No, gfn_to_pfn_prot() == FOLL_GET, kfp->pin == FOLL_PIN. But that's not really > relevant. > What I meant was, should we consider mte_copy_tags_from_user() as one that update the page contents (even though it is updating tags) and use kvm_follow_pfn() with kfp->pin = 1 instead? Is my understanding correct in that, if we want to look up a pfn/page from gfn with the intent of updating the page contents, we should use kfp->pin == 1? -aneesh