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 C849C7F for ; Wed, 14 Jun 2023 16:57:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E4801C433C8; Wed, 14 Jun 2023 16:57:57 +0000 (UTC) Date: Wed, 14 Jun 2023 17:57:55 +0100 From: Catalin Marinas To: Oliver Upton Cc: kvmarm@lists.linux.dev, Marc Zyngier , James Morse , Suzuki K Poulose , Zenghui Yu , Will Deacon , linux-arm-kernel@lists.infradead.org, Darren Hart , D Scott Phillips Subject: Re: [PATCH 0/3] KVM: arm64: Work around Ampere1 erratum AC03_CPU_38 Message-ID: References: <20230609220104.1836988-1-oliver.upton@linux.dev> 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 In-Reply-To: <20230609220104.1836988-1-oliver.upton@linux.dev> On Fri, Jun 09, 2023 at 10:01:01PM +0000, Oliver Upton wrote: > Small series to work around a CPU erratum on AmpereOne. While the > implementation does not advertise support for FEAT_HAFDBS (due to > another erratum), the associated control bits do not have RES0 behavior > as required by the architecture. > > Usage of HAFDBS at stage-1 is unaffected, since HA and HD are only > enabled on implementations that advertise the feature. However, KVM > relies on HA having RES0 semantics if the feature isn't implemented. The > end result is that KVM enables a broken hardware access flag > implementation that could lead to correctness issues. Just curious, what's the correctness issue here? The access flag is mostly indicative of which pages are old for swapping out/discarding. It's not like the dirty state which would be dangerous if we get wrong. -- Catalin