linux-kernel - Re: [PATCH 09/13] KVM: x86: save/load state on SMM switch

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Date:	Tue, 05 May 2015 15:18:48 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, bsd@...hat.com,
	guangrong.xiao@...ux.intel.com,
	Yang Zhang <yang.z.zhang@...el.com>, wanpeng.li@...ux.intel.com
Subject: Re: [PATCH 09/13] KVM: x86: save/load state on SMM switch



On 05/05/2015 14:48, Radim Krčmář wrote:
>>>> > > > +{
>>>> > > > +	desc->g    = (flags >> 15) & 1;
>>>> > > > +	desc->d    = (flags >> 14) & 1;
>>>> > > > +	desc->l    = (flags >> 13) & 1;
>>>> > > > +	desc->avl  = (flags >> 12) & 1;
>>>> > > > +	desc->p    = (flags >> 7) & 1;
>>>> > > > +	desc->dpl  = (flags >> 5) & 3;
>>>> > > > +	desc->s    = (flags >> 4) & 1;
>>>> > > > +	desc->type = flags & 15;
>>> > >
>>> > > I can't find a description of this ... can you point me to a place where
>>> > > the gap between 'p' and 'avl' is documented?
>>> > > (Not that it matters unless the guest reads it, but it's a bit weird.)
>> > 
>> > It turns out that access rights are stored in the same format as the VMX
>> > access rights.
> Thanks, so it really has a "reserved" space in the middle, to save some
> processing because the format is horrible (backward compatible).
> 
>> > access rights.  However, they are shifted by 8, which my code above
>> > doesn't do (bug).
> I think you are shifting it right, though ... they wouldn't fit into a
> word if shifted left.

Right, they have to be shifted right in the 64-bit case but not the
32-bit case.

Paolo
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