From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 A787F2D5C61 for ; Mon, 21 Jul 2025 13:12:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753103552; cv=none; b=XXxJYIMn/S6Wm3u7L+2BXKJoK0TU/NmPI4TyExjG4GHl4fl3Mvy1de+ss5LVb7rg1Kk4lU64mZtfSHJEhRLdKoj9BumjtWL+sk3ioSX1PmAZUr+eCwPAky/2Nm/q1nF7V+qs9E6iwU9TxL9A4vX2A7AEVv+H06Yu8znTbUxYoOU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753103552; c=relaxed/simple; bh=3nC713tAk8DTKDjaltrkzVufTB+8rPOtqlC2a9k6VPk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=cv9XrpD9xBH7HEdpXSgOg9LbBfjWQLKwF9daX7ci6ga/Tzl41OmwYTW2EXNDSCiKnwBjHUrGeAcGimv062Jbm/2+p/vyF/qccF51/j9HNcmspwNWgfQRsVlREeffO16Ya3Xg0vNZWgdU5VT4OpXZShuiVGKfSV3N9fmqjn8G9Iw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=WtFSjcy7; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="WtFSjcy7" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1753103549; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=/xaAjesXdXLCll4p8FaZte1EmjouFeib6o8XWb0yKk0=; b=WtFSjcy7yPONJXnq76rE9+FO5NdBHW7jrZGft+H77O+zXBIVV8KnGtv4Skb+xyqA9cVRzA /7GUDMzVEXAOi/BgGC7TIyGnCC5GF1J2UcuvH5jJXfzvZ0AENIkYMTt27dregAtUp0jEkO cRovHbvO3o7ABWGZirArTZZaQ1TWx2Y= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-490-e4NUjj3YNnqAnP1qIXKlpw-1; 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> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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.