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

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Date:	Tue, 05 May 2015 11:37:11 +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 04/05/2015 21:59, Radim Krčmář wrote:
> > The big ugly one.  This patch adds support for switching in and out of
> > system management mode, respectively upon receiving KVM_REQ_SMI and upon
> > executing a RSM instruction.  Both 32- and 64-bit formats are supported
> > for the SMM state save area.
> > 
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > ---
> > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> > +static void rsm_set_desc_flags(struct desc_struct *desc, u16 flags)
> > +{
> > +	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.  However, they are shifted by 8, which my code above
doesn't do (bug).

The documentation is, of course, QEMU and Bochs :) but you can also find
it in http://www.rcollins.org/ftp/source/include/struc.inc.  It is not
exactly for SMM, but it is more or less the same.

Paolo
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