From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9CF13D10F43 for ; Wed, 26 Nov 2025 13:00:36 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vOF88-0001F3-4v; Wed, 26 Nov 2025 08:00:22 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vOF7k-0000uW-GJ for qemu-devel@nongnu.org; Wed, 26 Nov 2025 07:59:59 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vOF7i-0001Ku-Bv for qemu-devel@nongnu.org; Wed, 26 Nov 2025 07:59:56 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1764161992; 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=SsjkXx6OaswXl8ikDM5Biep/jkNZbnax5RCRyj0b6nc=; b=G9Cwx1EL28Gf0E3+oF2aehj+/MRY86OaKvjLT7I8kOF165hRil3v0JVqb2pxvxOCa+P+1W F8K6w0mJFjWR1YsZWwUQcKtMKOrx8Ur3TkMc3DzziCwADfwF9AEypHtp7Bpf6HdYlr6ZT3 fqpBVicokqHPkRtcbJSgs3Y3kvLczpY= 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-201-8iKjtOhePgi6s_4qdjpJ8g-1; Wed, 26 Nov 2025 07:59:48 -0500 X-MC-Unique: 8iKjtOhePgi6s_4qdjpJ8g-1 X-Mimecast-MFC-AGG-ID: 8iKjtOhePgi6s_4qdjpJ8g_1764161988 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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 7C466180122B; Wed, 26 Nov 2025 12:59:47 +0000 (UTC) Received: from localhost (dhcp-192-239.str.redhat.com [10.33.192.239]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7238518004D8; Wed, 26 Nov 2025 12:59:46 +0000 (UTC) From: Cornelia Huck To: Peter Maydell Cc: qemu-arm@nongnu.org, qemu-devel@nongnu.org, Eric Auger Subject: Re: [PATCH for-11.0] arm: add DCZID_EL0 to idregs array In-Reply-To: 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: <20251119134414.2892640-1-cohuck@redhat.com> <87see2ozzu.fsf@redhat.com> User-Agent: Notmuch/0.38.3 (https://notmuchmail.org) Date: Wed, 26 Nov 2025 13:59:44 +0100 Message-ID: <875xaxosov.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.224, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Nov 25 2025, Peter Maydell wrote: > On Tue, 25 Nov 2025 at 16:09, Cornelia Huck wrote: >> >> On Mon, Nov 24 2025, Peter Maydell wrote: >> >> > On Wed, 19 Nov 2025 at 13:44, Cornelia Huck wrote: >> >> >> >> This requires a bit of care, since we still have to handle the EL >> >> specific part (DCZID_EL0.DZP). Callers can set/access dcz_blocksize >> >> via a wrapper working on DCZID_EL.BS. >> >> >> >> KVM currently does not support DCZID_EL0 via ONE_REG, and actually >> >> does not need to work with it, so provide a dummy value for now. >> > >> > That seems like an odd (unintended?) omission -- is it worth >> > adding? (We would need to handle older kernels that don't >> > expose it anyway, of course.) >> >> I'm not sure whether there's actually a usecase for KVM exposing this to >> the VMM - AFAICS, KVM doesn't do anything special for DC ZVA and >> friends, and doesn't tweak HCR_EL2.TDZ which would change behaviour. > > I guess the only one I can think of is to correctly fail > migration from a source CPU with a DCZID_EL0.BS that doesn't > match the one on the destination CPU. (We can't lie to the > guest about the blocksize as part of "tell the guest it has > a different CPU type from the actual host" unless we want to > trap and emulate all the DC ZVA etc insns...) Agreed. Might actually be best to assert that kvm code is not doing anything with the reg, rather than providing a dummy value. I'll respin.