Re: [PATCH] KVM: x86: Fix page-tables reserved bits

[Paolo Bonzini]

Il 17/04/2014 00:04, Marcelo Tosatti ha scritto:
> > > > > >> @@ -3550,9 +3550,9 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu,
> > > > > >>  		break;
> > > > > >>  	case PT64_ROOT_LEVEL:
> > > > > >>  		context->rsvd_bits_mask[0][3] = exb_bit_rsvd |
> > > > > >> -			rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
> > > > > >> +			rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 7);
> > > > > >>  		context->rsvd_bits_mask[0][2] = exb_bit_rsvd |
> > > > > >> -			rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
> > > > > >> +			rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 7);
> > > > >
> > > > > Bit 7 is not reserved either, for the PDPTE (its PageSize bit).
> > > > >
> > >
> > > In long mode (IA-32e), bit 7 is definitely reserved.

It's always reserved for PML4E (rsvd_bits_mask[x][3]), while for PDPTEs 
it is not reserved if you have 1GB pages.

> There is a separate reserved mask for PS=1, nevermind.

Yeah, but the situation for IA32e rsvd_bits_mask[0][2] is exactly the 
same as for PAE rsvd_bits_mask[0][1], and we're not marking the bit as 
reserved there.

The right thing to do is to add rsvd_bits(7, 7) to both 
rsvd_bits_mask[0][2] and rsvd_bits_mask[1][2], if 1GB pages are not 
supported.

As written, the patch has no effect on PDPTEs because 
rsvd_bits_mask[0][2] is only accessed if bit 7 is zero.

Nadav, would you mind preparing a follow-up?  Also, how did you find 
these issues and test the fixes?

Paolo
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