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([2a01:e0a:f0e:9070:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49989af26eesm31815315e9.15.2026.08.14.06.38.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Aug 2026 06:39:00 -0700 (PDT) Message-ID: <9909725f-7dd8-4f88-b016-2a6134906a60@redhat.com> Date: Fri, 14 Aug 2026 15:38:57 +0200 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: eric.auger@redhat.com Subject: Re: [RFC PATCH v3 16/19] qmp: add query-cpu-props-info command To: Khushit Shah , Markus Armbruster Cc: "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> From: Eric Auger In-Reply-To: <3099C064-6051-4B93-BE0F-C54B7FD91D82@nutanix.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ypnPLnoKpRCMGCboHpUuKdR9R_dhm0wxC_Xg3dT3dg4_1786714742 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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? Thanks Eric > > >