On Tue, Aug 10, 2021 at 09:51:31AM +0300, Valeriy Vdovin wrote: > From: Valeriy Vdovin <valeriy.vdovin@xxxxxxxxxxxxx> > > Introducing new QMP command 'query-x86-cpuid'. This command can be used to > get virtualized cpu model info generated by QEMU during VM initialization in > the form of cpuid representation. > > Diving into more details about virtual CPU generation: QEMU first parses '-cpu' > command line option. From there it takes the name of the model as the basis for > feature set of the new virtual CPU. After that it uses trailing '-cpu' options, > that state if additional cpu features should be present on the virtual CPU or > excluded from it (tokens '+'/'-' or '=on'/'=off'). > After that QEMU checks if the host's cpu can actually support the derived > feature set and applies host limitations to it. > After this initialization procedure, virtual CPU has it's model and > vendor names, and a working feature set and is ready for identification > instructions such as CPUID. > > To learn exactly how virtual CPU is presented to the guest machine via CPUID > instruction, new QMP command can be used. By calling 'query-x86-cpuid' > command, one can get a full listing of all CPUID leaves with subleaves which are > supported by the initialized virtual CPU. > > Other than debug, the command is useful in cases when we would like to > utilize QEMU's virtual CPU initialization routines and put the retrieved > values into kernel CPUID overriding mechanics for more precise control > over how various processes perceive its underlying hardware with > container processes as a good example. > > The command is specific to x86. It is currenly only implemented for KVM acceleator. > > Output format: > The output is a plain list of leaf/subleaf argument combinations, that > return 4 words in registers EAX, EBX, ECX, EDX. > [...] Based on the effort being required from you to make sure this patch is in good shape, maybe you could reconsider my suggestion from a while ago for a single-CPUID-leaf interface, as discussed at: https://lore.kernel.org/qemu-devel/20210421201759.utsmhuopdmlhghbx@xxxxxxxxxxx/ A single-CPUID-leaf qmp_query_x86_cpuid() function that is generic and not KVM-specific can probably be implemented in ~5 lines of code. I'm not against the interface proposed here, but you are surely going to get more friction and more complexity to deal with. -- Eduardo
