Re: [Xen-devel] [PATCH v3 2/4] x86/compat: Test both PV and PVH guests for compat mode

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/23/2015 10:07 AM, Jan Beulich wrote:
> > > > On 11.07.15 at 00:20, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > Add is_pvh_32bit_domain() macro and use it alongside is_pv_32bit_domain()
> > where necessary.
> >
> > Since PVH guests cannot change execution mode, has_32bit_shinfo is a good
> > indicator of whether the guest is PVH and 32-bit.
> >
> > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Relative to what is in the tree right now this is fine, but ...
>
> > @@ -771,7 +771,7 @@ int arch_set_info_guest(
> >   
> >       /* The context is a compat-mode one if the target domain is compat-mode;
> >        * we expect the tools to DTRT even in compat-mode callers. */
> > -    compat = is_pv_32bit_domain(d);
> > +    compat = is_pv_32bit_domain(d) || is_pvh_32bit_domain(d);
> ... won't this and ...
>
> > @@ -1203,7 +1204,7 @@ void arch_get_info_guest(struct vcpu *v, 
> > vcpu_guest_context_u c)
> >   {
> >       unsigned int i;
> >       const struct domain *d = v->domain;
> > -    bool_t compat = is_pv_32bit_domain(d);
> > +    bool_t compat = is_pv_32bit_domain(d) || is_pvh_32bit_domain(d);
> ... this get in the way of what we called "no-pm" on yesterday's call?
I made no effort to make this workable for "no-dm" case. This will 
probably need to be adjusted when that code gets in. IIRC this new code 
has a flag (or something along those lines) that will allow us to 
distinguish PVH-"classic" vs. "no-dm".
> I would assume that for the transitional period both ought to be able
> to co-exist.

Yes, but I suspect this will not be the only place where we will need to 
have different code paths for the two approaches. hvm_set_cr0(), for 
example, doesn't allow PVH guests to switch modes.

> Plus - is this in line with what the tools are doing? Aren't they
> assuming !PV <=> native format context? I.e. don't you need
> to treat differently v->domain == current->domain and its
> opposite? Roger btw. raised a similar question on IRC earlier
> today...
Not sure I understand this. You mean for copying 64-bit guest's info 
into 32-bit dom0?
-boris


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