Re: [Xen-devel] [PATCH v2 1/4] x86/compat: Test whether guest has 32b shinfo instead of being a PV 32b domain

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/09/2015 10:30 AM, Boris Ostrovsky wrote:
> On 07/09/2015 10:17 AM, Jan Beulich wrote:
> > > > > On 09.07.15 at 16:10, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > On 07/09/2015 03:02 AM, Jan Beulich wrote:
> > > > > > > On 08.07.15 at 22:57, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > > > As I started to update the patches I realized that in some cases
> > > > > (especially in arch_do_domctl():XEN_DOMCTL_get_address_size) we don't
> > > > > have VCPU (which is what hvm_guest_x86_mode() wants) but rather 
> > > > > only the
> > > > > domain. d->vcpu[0] should work. Otherwise I'll either need a new 
> > > > > field
> > > > > in struct domain or wrap has_32bit_shinfo into something 
> > > > > PVH-specific,
> > > > > like is_32bit_pvh_vcpu().
> > > > Shouldn't XEN_DOMCTL_get_address_size be handled HVM-like
> > > > for PVH, especially if you also intend the tools to use the 64-bit
> > > > guest context variant even for 32-bit PVH? Once again - are you
> > > > intending to prohibit 32-bit PVH switching to 64-bit mode (which
> > > > would seem both wrong and possibly cumbersome to me)?
> > > With current PVH implementation I don't think we can switch. We are
> > > starting the guest in very much PV-like fashion. That's why we are
> > > getting into switch_compat() --- via XEN_DOMCTL_set_address_size.
> > >
> > > For XEN_DOMCTL_get_address_size specifically we need to be able to
> > > figure out the mode *before* the guest is running because we use it to
> > > set cpuid bits in xc_cpuid_pv_policy(). So just that means we can't
> > > change the mode.
> > Okay - but is there code (being put) in place to refuse switch
> > attempts?
> No, I should add code to deal with this.
Forgot to include here --- so what is your preference wrt what I am 
asking in the first paragraph? d->vcpu[0], new field (or maybe a flag 
with bits per 32bit-pv and 32bit-pvh), or a PVH-wrapper for 
has_32bit_shinfo?
-boris

-boris


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