Messages in this thread | | | Subject | Re: [PATCH] KVM: VMX: Use wrapper macro ~RMODE_GUEST_OWNED_EFLAGS_BITS directly | From | Paolo Bonzini <> | Date | Fri, 6 Mar 2020 11:00:12 +0100 |
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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
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