Re: [PATCH] KVM: VMX: Use wrapper macro ~RMODE_GUEST_OWNED_EFLAGS_BITS directly

[Paolo Bonzini]

On 06/03/20 10:44, Vitaly Kuznetsov wrote:
>>> Define a macro RMODE_HOST_OWNED_EFLAGS_BITS for (X86_EFLAGS_IOPL |
>>> X86_EFLAGS_VM) as suggested by Vitaly seems a good way to fix this ?
>>> Thanks.
>> No, what if a host-owned flag was zero?  I'd just leave it as is.
>>
> I'm not saying my suggestion was a good idea but honestly I'm failing to
> wrap my head around this. The suggested 'RMODE_HOST_OWNED_EFLAGS_BITS'
> would just be a define for (X86_EFLAGS_IOPL | X86_EFLAGS_VM) so
> technically the patch would just be nop, no?

It would not be a nop for the reader.

Something called RMODE_{GUEST,HOST}_OWNED_EFLAGS_BITS is a mask.  It
tells you nothing about whether those bugs are 0 or 1.  It's just by
chance that all three host-owned EFLAGS bits are 1 while in real mode.
It wouldn't be the case if, for example, we ran the guest using vm86
mode extensions (i.e. setting CR4.VME=1).  Then VIF would be host-owned,
but it wouldn't necessarily be 1.

Paolo