Re: [PATCH 1/4] kvm: nVMX: Add support for "VMWRITE to any supported field"

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On Wed, May 2, 2018 at 9:02 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> On 02/05/2018 17:52, Jim Mattson wrote:
>>>> vmcs_field_readonly is now unused.  With that removed,
>>>>
>>>> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>>> Actually, no.  The error must be kept if the host has disabled the
>>> feature with a KVM_SET_MSR ioctl for MSR_IA32_VMX_MISC.
>>>
>> Coming back to this patch set...
>>
>> Is there a good reason to allow userspace to clear
>> MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS? It's not yet possible to
>> migrate a VMX-capable VM (though I think that ability is imminent), so
>> there are no compatibility issues. Why not just force this on?
>
> I suppose that can be done, yes.  The only reason is that silicon ties
> that bit to the availability of shadow VMCS, but we can certainly do
> things differently than actual processors.
>
> Technically it would be a small userspace API break, but we can live
> with it.

Does qemu explicitly set IA32_VMX_MISC today?



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