From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=217.140.110.172 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793361074; b=mzH22y/ILrSlAROnxdJpCmC06NacrtgDTrXOR0sMNxkzBJlpzne9lXBdvjcN18WgS2yF jGqFv8YO3kKv65CGO7udKRZ1BLYFYJUJN+dTdr9+lJDZJKZJ9YmwwLWilLWoT9lLIaATP 8fd3ryuqvnO/cczORwJrlN3okcjL8VVq8D8+xyMo29KovWZhEULmnbOdfHay66mOPeZOE 8+nTDU9FN7cA0oOjcV9elHBaMs5awfzMibaFN+HabBB8ln1MBFDVdtQBVkhZBdBhy/zpZ SGNnGX3Atp4P2wUIykhiM3+bssqcZzzwaw/qM/ral+T8C14n5fmIeMjkzexlnaKabmA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793361074; h=DMARC-Filter:Received:Received:DKIM-Signature:From:To:Cc:Subject: Date:Message-ID:X-Mailer:In-Reply-To:References:MIME-Version: Content-Type:Content-Disposition:Content-Transfer-Encoding; bh=EV9q3xMYUg7eyUdptCPQkT+NInqEVi2Bft0i/3u9pWc=; b=S6SpWoUqDp965fHzlKbuZ7dOx+J6689TyPB8sSWGGfl2qhHmJTG1T7LsS2kYt4JYVQVU df7FO1w84x/aNgsgmZAD8PAZuHfgXGL0ghBsnQasJK8u0lC1Rl7BsX6r4v5efJ2dKDVTt ZimjCXeoFhBhiC3BWBru3YBmdHen7xhwrHpb7eXRMGsg8dPSL+UJdBS2yq3VPkUrqek1C 58Dg7Sbnm2MiMngwrT7L++gJhwKuOG7MPnkeYYJSi0I628dWJ8+sW/IzSdGQKqYNwqDbf mHce/i/8xokVMe2e2NDo7Pmy4mef6k+6EgW16VOkuXAWYqeC8RSSkq6Hvob5zHkXP6Q== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=lhbs403c; arc=none smtp.remote-ip=217.140.110.172 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id A7504606A31A for ; Fri, 30 Oct 2026 11:51:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org A7504606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=lhbs403c Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2A79E1682; Fri, 30 Oct 2026 04:51:10 -0700 (PDT) Received: from LeoBrasDK.cambridge.arm.com (LeoBrasDK.cambridge.arm.com [10.2.212.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A3AE73F7B4; Fri, 30 Oct 2026 04:51:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1793361073; bh=Mc3ZxWgjpeC+0tTsnex0ZyBfJ8y4oR4Ncako7tOwxzw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lhbs403ceP0i6J8ZnKQpDhpeznmarJmBUeflvdmtHnlB2nPAIKDzzcVGkjSj9dQ7W vtYBO7rtqa2fVQpvzW5QK31u40tMnW4Jc2IGyVrESGNTwnIebruQEJnQGn+OPTDhPw Gf2ge37yfRyKGQJ5KxdYYDrHf/8gyFWRm3p7HOp4= From: Leonardo Bras To: Tian Zheng Cc: Leonardo Bras , liuyonglong , Oliver Upton , Marc Zyngier , Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Mark Rutland , Raghavendra Rao Ananta , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Zhou Wang Subject: Re: [RFC PATCH 5/5] KVM: arm64: Enable HAFDBS for guests not on migration Date: Fri, 30 Oct 2026 11:51:08 +0000 Message-ID: X-Mailer: git-send-email 2.56.0 In-Reply-To: References: <3e464bef-8dfe-44a3-afea-3c276ae87cd8@huawei.com> <8eaaba87-7881-49c4-a76a-51dec2f29ffc@huawei.com> <52945586-8c5c-4991-bd92-fe02aaf79fbe@huawei.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 Content-Transfer-Encoding: 8bit On Fri, Oct 30, 2026 at 02:01:49PM +0800, Tian Zheng wrote: > > > On 10/29/2026 7:54 PM, Leonardo Bras wrote: > > On Thu, Oct 29, 2026 at 10:54:24AM +0800, Tian Zheng wrote: > > > Hi Leo, > > > > > > I've read your discussion with Oliver on DBM RFC v2. As a suggestion, > > > maybe we should go with Oliver's approach, i.e. revert to the v1 scheme > > > and continue fixing from there. > > > > Hi Tian, > > I have been reading a bit more about permission indirection to try figuring > > out a way that the change may work for both ways. > > > > The problem with the previous approach is that it assume DBM=write at all > > times, which is not architecturally correct. Having DBM=write only on > > HAFDBS=on as suggested would require us to transverse the whole pagetable > > to convert encodings when we enable/disable it, which can be quite > > expensive. > > > > One option would be to always enable HAFDBS when system supports HDBSS, but > > I still have to figure out if that causes any performance regression before > > suggesting. > > > > The option I am pursuing is thinking on an unified code path for direct > > permissison (both HACDBS=on and HACDBS=off) so we don't have to convert > > between them, neither worry about the impact of HAFDBS=on on performance. > > > > I will reply on the thread once I figure one of those options out. > > > > Thanks! > > Leo > > Hi Leo, > > Sounds good. I'll wait for your next version and review it once it's > posted. > > Thanks, > Tian Awesome, thanks! Leo