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([2a01:e0a:f0e:9070:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482bf82594esm267911f8f.29.2026.08.20.09.01.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Aug 2026 09:01:36 -0700 (PDT) Message-ID: <9ac6089a-2dad-441b-8ec7-f6c03cdad312@redhat.com> Date: Thu, 20 Aug 2026 18:01:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 16/19] qmp: add query-cpu-props-info command To: Khushit Shah Cc: Markus Armbruster , "qemu-devel@nongnu.org" , "qemu-arm@nongnu.org" , "kvmarm@lists.linux.dev" , "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 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> <9909725f-7dd8-4f88-b016-2a6134906a60@redhat.com> <676C0BA3-A842-4784-84D2-8B446E8CAB67@nutanix.com> From: Eric Auger In-Reply-To: <676C0BA3-A842-4784-84D2-8B446E8CAB67@nutanix.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: hjv5UNOOLMwtnugb3l3M6Cyp2fC1sRrjDpPZDXrwvOg_1787241697 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=eric.auger@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.346, 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, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: eric.auger@redhat.com Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On 8/18/26 11:46 AM, Khushit Shah wrote: > >> On 14 Aug 2026, at 7:08 PM, Eric Auger wrote: >> >> !-------------------------------------------------------------------| >> CAUTION: External Email >> >> |-------------------------------------------------------------------! >> >> Hi Khushit, >> >> On 8/5/26 8:47 AM, Khushit Shah wrote: >>>> On 4 Aug 2026, at 12:15 PM, Markus Armbruster wrote: >>>> >>>> !-------------------------------------------------------------------| >>>> CAUTION: External Email >>>> >>>> |-------------------------------------------------------------------! >>>> >>>> Khushit Shah writes: >>>> >>>>> Introduce the 'query-cpu-props-info' QMP command. For CPU model >>>>> properties it reports the type (boolean or number) and the set of values >>>>> supported under the active accelerator and host. >>>>> >>>>> 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. >>>>> >>>>> 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. >>>>> >>>>> 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. >>>>> >>>>> Signed-off-by: Khushit Shah >>>> 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. >> How does x86 handle this at the moment, they don't have the cmd either? >> How do they currently introspect what are the valid values for a >> specific host? Is it easier for them? > x86 is much simpler, all the cpu features properties are backed by cpuid bits > and assumption is simple, if host value is “true”, “false" is supported, and > if the host value is “false", “true" is not supported. OK thanks! Eric > > Warm Regards, > Khushit >> >> Thanks >> >> Eric >>> >>>