2015-05-05 11:37+0200, Paolo Bonzini:
> 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@xxxxxxxxxx>
> > > ---
> > > 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.
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.
(I'd just shorten it after finding the right name for mask
u32 mask = 0x00f0ff00
desc->b = desc->b & ~mask | flags << 8 & mask
and maybe define 'attributes' field in desc that is already shifted.)
> 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.
(It's a register hidden from software, so I have some trust issues :])
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