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 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.
-boris

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