From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2BECD330666 for ; Mon, 29 Jun 2026 10:30:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782729013; cv=none; b=NooEn6cmAwrsFgGywfPA9BtrlN4C9mWDOVQunMspRjIIiLaMoQOhuGa1E8Bb9zepJDWR8gC3Aht5pwJhOPAmww9WI6T2nXOrqLIjNz6xSska/F0Hb9pOcQcpSQf9t3+Ty7DEdRqDxE7EZ49MCq2yqvNnsl4h3rlqdDu0hp2dZKw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782729013; c=relaxed/simple; bh=Ds6nJwSE6DlTJOVLmnCEfT6iaTAaF5KKMPl6oD7/81I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type:Content-Disposition; b=QFbapDmCAZz9na333ugUQRqXJ6sPFrn1qrMRErey+h0E0jLSsVh+FXZHAvnYc7TvHH+4O+qR1HDhFGMCs0khZKBdiEQzh/87+gahP/EfkP4P0QP9cOiyyp854TKMC/vW4FFmDxTtZSwL1PGvHTEZAtLzeuvG+GDqTBBJHfvHzOs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=vB6G5fRK; arc=none smtp.client-ip=217.140.110.172 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) header.d=arm.com header.i=@arm.com header.b="vB6G5fRK" 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 E8CAC176C; Mon, 29 Jun 2026 03:30:06 -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 418263F836; Mon, 29 Jun 2026 03:30:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1782729011; bh=Ds6nJwSE6DlTJOVLmnCEfT6iaTAaF5KKMPl6oD7/81I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vB6G5fRKn9k3DSsZ9kNIFzcAuSNXA10J9wQsTq/LFe/mWIQ48TDRIOCzdG4V9/9el co63LfgLjYKeghuLBK4QyEv1HbEj8vlc0zfU61Ues9mvX2vGoshJAJ1s56gZpv/UF4 /AxNl+k/45UD7xM2g5uXRP3JCy4xJWRXVYTZh1wg= From: Leonardo Bras To: Marc Zyngier Cc: Leonardo Bras , Oliver Upton , kvmarm@lists.linux.dev, Joey Gouly , Suzuki K Poulose , Zenghui Yu , Wei-Lin Chang , Steffen Eiden Subject: Re: [PATCH 00/22] KVM: arm64: nv: Implement FEAT_HAFDBS, FEAT_HAFT Date: Mon, 29 Jun 2026 11:29:50 +0100 Message-ID: X-Mailer: git-send-email 2.54.0 In-Reply-To: <8633y9ql8q.wl-maz@kernel.org> References: <20260623184201.1518871-1-oupton@kernel.org> <8633y9ql8q.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit On Fri, Jun 26, 2026 at 06:12:21PM +0100, Marc Zyngier wrote: > On Fri, 26 Jun 2026 16:31:50 +0100, > Leonardo Bras wrote: > > > > On Tue, Jun 23, 2026 at 11:41:39AM -0700, Oliver Upton wrote: > > > KVM's support for hardware descriptor updates has been lacking, owing in > > > large part to the fact that the most widely available NV2 hardware > > > actually lacks HAFDBS :) > > > > > > This series brings support for hardware dirty state and table Access > > > flags to the nested MMU. While KVM uses neither of these features, the > > > kernel definitely does in the stage-1 page tables. Since there is only > > > one hypervisor to rule them all, implementing this stuff at stage-2 is > > > mostly motivated by the desire to enable guest stage-1 :) > > > > > > Implementing dirty state at stage-2 is a bit more challenging than > > > anticipated, I'm in the middle of seeking a relaxation from Arm that > > > would make this all architectural. See the last patch for the details. > > > > Hi Oliver, > > > > Haven't read your patchset yet, but in regards to stage-2 dirty-state > > tracking, there have already been some efforts in the area, also > > implementing HDBSS and HACDBS in a way of improving performance / reducing > > impact of live migration on a system. > > I'm worried you are reading this series the wrong way. This is mostly > orthogonal to the whole HDBSS/HACDBS/SLAUA (Super Long And > Unpronounceable Acronym). Oh wait, you haven't read it yet. Great :-(. Sorry, I have very little understanding of nested, and I wrongly thought this patchset would be in some way also involve hw-accelerated dirty-bit usage. > > This series is about *implementing* HAFDBS and HAFT in NV. We can't > rely on the HW setting the AF and DB in the guest's own S2 PTs, > because these page tables are never live. So we have to do it > ourselves. Got it! > > So this has nothing to do with S2 dirty tracking for the purpose of > migration. The guest could implement its own migration based on that, > but that has nothing to do with what this series is doing. > Makes sense. Thanks for clarifying this, and for your patience. Leo