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Wed, 05 Aug 2026 02:57:27 -0400 X-MC-Unique: XnzXpwKLNGmgUgnka3LzkA-1 X-Mimecast-MFC-AGG-ID: XnzXpwKLNGmgUgnka3LzkA_1785913045 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E49801956095; Wed, 5 Aug 2026 06:57:23 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.7]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C914E18005A7; Wed, 5 Aug 2026 06:57:22 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 3DC5C21E6920; Wed, 05 Aug 2026 08:57:20 +0200 (CEST) From: Markus Armbruster To: Khushit Shah Cc: "qemu-devel@nongnu.org" , "qemu-arm@nongnu.org" , "kvmarm@lists.linux.dev" , "eric.auger@redhat.com" , "cohuck@redhat.com" , "peter.maydell@linaro.org" , "richard.henderson@linaro.org" , "maz@kernel.org" , "oliver.upton@linux.dev" , "berrange@redhat.com" , "abologna@redhat.com" , "jdenemar@redhat.com" , "gshan@redhat.com" , "skolothumtho@nvidia.com" , "sebott@redhat.com" , "philmd@linaro.org" , "yangjinqian1@huawei.com" , Shaju Abraham , Mark Cave-Ayland , Prerna Saxena Subject: Re: [RFC PATCH v3 16/19] qmp: add query-cpu-props-info command In-Reply-To: <3099C064-6051-4B93-BE0F-C54B7FD91D82@nutanix.com> (Khushit Shah's message of "Wed, 5 Aug 2026 06:47:52 +0000") References: <20260716213858.609699-1-khushit.shah@nutanix.com> <20260716213858.609699-17-khushit.shah@nutanix.com> <878q6m5qox.fsf@pond.sub.org> <3099C064-6051-4B93-BE0F-C54B7FD91D82@nutanix.com> Date: Wed, 05 Aug 2026 08:57:20 +0200 Message-ID: <875x1p12cv.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 127.0.0.2 X-Mimecast-MFC-PROC-ID: suUxHB4j5hKRBT-IiulzNJnWjXBT5K1GCiG3FESjLVA_1785913045 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Khushit Shah writes: >> On 4 Aug 2026, at 12:15=E2=80=AFPM, Markus Armbruster wrote: >>=20 >> !-------------------------------------------------------------------| >> CAUTION: External Email >>=20 >> |-------------------------------------------------------------------! >>=20 >> Khushit Shah writes: >>=20 >>> Introduce the 'query-cpu-props-info' QMP command. For CPU model >>> properties it reports the type (boolean or number) and the set of value= s >>> supported under the active accelerator and host. >>>=20 >>> For numbers the supported values are expressed as a list of inclusive >>> {min, max} ranges; for booleans as the list of allowed true/false >>> values. >>>=20 >>> The command and its return types (CpuPropertyType, CpuPropertyInfo and >>> friends) are defined in qapi/machine.json rather than an Arm-specific >>> schema, since the concept applies to other targets (e.g. x86, riscv) >>> too. Target that do not implement it return an error. >>>=20 >>> The Arm/KVM implementation spins up a scratch "host" vCPU object, >>> walks its QOM properties: SYSREG_ ID-register fields become 'number' >>> properties whose ranges come from arm_field_get_supported_values(), >>> and the advertised feature toggles become 'boolean' properties. >>>=20 >>> Signed-off-by: Khushit Shah >>=20 >> This explains what the command does and how it's implemented. It's >> silent on the most important aspect: why do we want the command? What >> is its intended purpose? > > Will add something like: > > This helps the management stack to discover which values are supported > for a given CPU property. This is especially important for non-boolean > properties, where knowing that the host has value 'x' does not inherently > reveal the full range of valid values supported on the host. Better. Perhaps throw in an example if you can come up with a simple one.