Messages in this thread | | | Subject | Re: KVM_SET_CPUID doesn't check supported bits (was Re: [PATCH 0/6] KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup) | From | stsp <> | Date | Mon, 7 Dec 2020 14:47:28 +0300 |
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07.12.2020 14:29, Paolo Bonzini пишет: > On 07/12/20 12:24, stsp wrote: >> It tries to enable VME among other things. >> qemu appears to disable VME by default, >> unless you do "-cpu host". So we have a situation where >> the host (which is qemu) doesn't have VME, >> and guest (dosemu) is trying to enable it. >> Now obviously KVM_SET_CPUID doesn't check anyting >> at all and returns success. That later turns >> into an invalid guest state. >> >> >> Question: should KVM_SET_CPUID check for >> supported bits, end return error if not everything >> is supported? > > No, it is intentional. Most bits of CPUID are not ever checked by > KVM, so userspace is supposed to set values that makes sense By "that makes sense" you probably meant to say "bits_that_makes_sense masked with the ones returned by KVM_GET_SUPPORTED_CPUID"?
So am I right that KVM_SET_CPUID only "lowers" the supported bits? In which case I don't need to call it at all, but instead just call KVM_GET_SUPPORTED_CPUID and see if the needed bits are supported, and exit otherwise, right?
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