From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 143CD27A442 for ; Wed, 14 May 2025 18:22:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747246948; cv=none; b=Veyveyb7giy95nl0vlZu2fcE8Y2bn7vrgcjvIwExvFYZIi+F+4UawTWMBUrVZiZFu9ao1Fc7GZ4oMv1AWt6/eJ4aN6/Hutzgh7A7Ow26RLSp1pHINdtSjsLhO5H8+XBDdHtM3K6Xd8/5JL/x6/NzgHufZfEs2wk7jjI7LohG+Pw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747246948; c=relaxed/simple; bh=jbmaLe1rODb+DtAQ61FQd/wuKOVV4JndU4jbbUNACKk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OdROfM+8cJrt9YmH4b8/snVYrW69sfB1pmZeJK4ENw4yErbjWrjK3KE/wjOD7aZ4D9D2zahexXrCPM44mCX3W+Fzvyhq7pvkVwY7K3Ergb+9PN4lT9yBHWPFs+g8ZuYLvH13H2NlnyLC5CcFobJNti2M+YUEkKR6Ld0ErmXZseM= 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=EKVNiE72; arc=none smtp.client-ip=170.10.129.124 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="EKVNiE72" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1747246946; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=tPeRMIcrtB8JtU0o7I5k5bCudFUZhP2qzhPFFnVn9pE=; b=EKVNiE72Cy3wmqt8OyEHdmtNYo5CQFb7hDV/Jg97CSVnbYZ7XmANrFpf7BnzXIPMJu0mWc y2vtfAwc77iWMYBvUvOfKm3KoyxVcbOD49Os8gCUY1Y6tpRezLMw+EMqnTtXTs8jfIYJCQ 3N4zqDJVtDFuMbHW4ydYNKChoSf+1VE= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-621-XgSVwa3ROS2hjrpefnarRA-1; Wed, 14 May 2025 14:22:22 -0400 X-MC-Unique: XgSVwa3ROS2hjrpefnarRA-1 X-Mimecast-MFC-AGG-ID: XgSVwa3ROS2hjrpefnarRA_1747246940 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4DA9B1956050; Wed, 14 May 2025 18:22:19 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.22]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E940A180087A; Wed, 14 May 2025 18:22:11 +0000 (UTC) Date: Wed, 14 May 2025 19:22:08 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Cornelia Huck Cc: eric.auger.pro@gmail.com, eric.auger@redhat.com, qemu-devel@nongnu.org, qemu-arm@nongnu.org, kvmarm@lists.linux.dev, peter.maydell@linaro.org, richard.henderson@linaro.org, alex.bennee@linaro.org, maz@kernel.org, oliver.upton@linux.dev, sebott@redhat.com, shameerali.kolothum.thodi@huawei.com, armbru@redhat.com, abologna@redhat.com, jdenemar@redhat.com, agraf@csgraf.de, shahuang@redhat.com, mark.rutland@arm.com, philmd@linaro.org, pbonzini@redhat.com Subject: Re: [PATCH v3 08/10] arm/cpu: more customization for the kvm host cpu model Message-ID: Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20250414163849.321857-1-cohuck@redhat.com> <20250414163849.321857-9-cohuck@redhat.com> <875xi3cig5.fsf@redhat.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <875xi3cig5.fsf@redhat.com> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On Wed, May 14, 2025 at 05:36:58PM +0200, Cornelia Huck wrote: > On Tue, May 13 2025, Daniel P. Berrangé wrote: > > > On Mon, Apr 14, 2025 at 06:38:47PM +0200, Cornelia Huck wrote: > >> From: Eric Auger > >> > >> If the interface for writable ID registers is available, expose uint64 > >> SYSREG properties for writable ID reg fields exposed by the host > >> kernel. Properties are named SYSREG__ with REG and FIELD > >> being those used in linux arch/arm64/tools/sysreg. This done by > >> matching the writable fields retrieved from the host kernel against the > >> generated description of sysregs. > >> > >> An example of invocation is: > >> -cpu host,SYSREG_ID_AA64ISAR0_EL1_DP=0x0 > >> which sets DP field of ID_AA64ISAR0_EL1 to 0. > > > > For the value you are illustrating 0x0 - is this implying that > > all the flags take an arbitrary integer hex value ? > > > > This would be different from x86, where CPU feature flags are > > a boolean on/off state. > > Most of the fields are 4 bits, the allowed values vary (there are also > some fields that are single bits, or wider.) The FEAT_xxx values (which > can be expressed via ID register fields, or a combination thereof) are > mostly boolean, but there are also some of them that can take values. > > We could cook up pseudo-features that are always on/off, but I don't > like that approach: they would be QEMU only, whereas the ID register > fields and FEAT_xxx features are all defined in the Arm documentation. Fortunately from a libvirt POV we can likely expand our config to cope with hex values for arm features without too much trouble. > > An additional difference from x86 would be that FEAT_xxx featues are not > neccessarily configurable (only if the host kernel supports changing the > ID register field(s) backing the feature.) Is the kernel able to tell us which ones are configurable and which are not ? If so, it'd be helpful to expose this info in QAPI some place. > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|