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Mon, 21 Jul 2025 09:12:26 -0400 X-MC-Unique: e4NUjj3YNnqAnP1qIXKlpw-1 X-Mimecast-MFC-AGG-ID: e4NUjj3YNnqAnP1qIXKlpw_1753103544 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C8E4A18009F8; Mon, 21 Jul 2025 13:12:23 +0000 (UTC) Received: from localhost (pixel-6a.str.redhat.com [10.33.192.205]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5F35019560B3; Mon, 21 Jul 2025 13:12:22 +0000 (UTC) From: Cornelia Huck To: Marc Zyngier Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, Joey Gouly , Suzuki K Poulose , Oliver Upton , Zenghui Yu , Will Deacon , Catalin Marinas Subject: Re: [PATCH 6/7] KVM: arm64: Expose FEAT_RASv1p1 in a canonical manner In-Reply-To: <86o6td8zzq.wl-maz@kernel.org> Organization: "Red Hat GmbH, Sitz: Werner-von-Siemens-Ring 12, D-85630 Grasbrunn, Handelsregister: Amtsgericht =?utf-8?Q?M=C3=BCnchen=2C?= HRB 153243, =?utf-8?Q?Gesch=C3=A4ftsf=C3=BChrer=3A?= Ryan Barnhart, Charles Cachera, Avril Crosse O'Flaherty" References: <20250721101955.535159-1-maz@kernel.org> <20250721101955.535159-7-maz@kernel.org> <87seip67xz.fsf@redhat.com> <86o6td8zzq.wl-maz@kernel.org> User-Agent: Notmuch/0.38.3 (https://notmuchmail.org) Date: Mon, 21 Jul 2025 15:12:19 +0200 Message-ID: <87pldt6630.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250721_061231_162272_598D0E2A X-CRM114-Status: GOOD ( 14.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jul 21 2025, Marc Zyngier wrote: > On Mon, 21 Jul 2025 13:32:08 +0100, > Cornelia Huck wrote: >> >> On Mon, Jul 21 2025, Marc Zyngier wrote: >> >> > If we have RASv1p1 on the host, advertise it to the guest in the >> > "canonical way", by setting ID_AA64PFR0_EL1 to V1P1, rather than >> > the convoluted RAS+RAS_frac method. >> >> Don't the two methods have slightly different semantics with RAS == V1P1 >> possibly implying FEAT_DoubleFault, and RAS+RAS_frac not? > > Ah, that's an interesting point -- I definitely had glanced over that. > > But I'm not sure a guest can actually distinguish between these two > configurations, given that FEAT_DoubleFault is essentially an EL3 > feature (as indicated in the RAS == V1P1 section, and further > confirmed in R_GRJVN), making it invisible to the guest. > > FEAT_DoubleFault2 is, on the contrary, totally visible from the guest, > and independent of EL3. > > Does this make sense to you? It does; but it might make sense to add a comment explaining that. Userspace should hopefully be able to just map everything to RAS == V1P1 and be done with it.