Re: [Xen-devel] [PATCH for-next v3 9/9] x86: introduce CONFIG_HYPERV and detection code

[Wei Liu <wl@xxxxxxx>]

On Fri, Nov 15, 2019 at 03:07:29PM +0100, Jan Beulich wrote:
> On 21.10.2019 17:57, Wei Liu wrote:
> > --- a/xen/arch/x86/Kconfig
> > +++ b/xen/arch/x86/Kconfig
> > @@ -164,6 +164,15 @@ endchoice
> >  config GUEST
> >     bool
> >  
> > +config HYPERV_GUEST
> > +   def_bool n
> > +   select GUEST
> > +   prompt "Hyper-V Guest"
> 
> Please can you avoid following the bad example XEN_GUEST gives (and
> perhaps even take the opportunity here or in the earlier patch
> adding GUEST to change that one as well)? What you want is
> 
> config HYPERV_GUEST
>       bool "Hyper-V Guest"
>       select GUEST

Ack.

> 
> > --- /dev/null
> > +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> > @@ -0,0 +1,54 @@
> > +/******************************************************************************
> > + * arch/x86/guest/hyperv/hyperv.c
> > + *
> > + * Support for detecting and running under Hyper-V.
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; either version 2 of the License, or
> > + * (at your option) any later version.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program; If not, see <http://www.gnu.org/licenses/>.
> > + *
> > + * Copyright (c) 2019 Microsoft.
> > + */
> > +#include <xen/init.h>
> > +
> > +#include <asm/guest.h>
> > +
> > +bool __init hyperv_probe(void)
> > +{
> > +    uint32_t eax, ebx, ecx, edx;
> > +
> > +    cpuid(0x40000000, &eax, &ebx, &ecx, &edx);
> > +    if ( !((ebx == 0x7263694d) &&  /* "Micr" */
> > +           (ecx == 0x666f736f) &&  /* "osof" */
> > +           (edx == 0x76482074)) )  /* "t Hv" */
> > +        return false;
> > +
> > +    cpuid(0x40000001, &eax, &ebx, &ecx, &edx);
> > +    if ( eax != 0x31237648 )    /* Hv#1 */
> > +        return false;
> > +
> > +    return true;
> > +}
> > +
> > +struct hypervisor_ops hyperv_ops = {
> 
> const again.
> 
> > --- a/xen/arch/x86/guest/hypervisor.c
> > +++ b/xen/arch/x86/guest/hypervisor.c
> > @@ -43,6 +43,14 @@ bool hypervisor_probe(void)
> >      }
> >  #endif
> >  
> > +#ifdef CONFIG_HYPERV_GUEST
> > +    if ( hyperv_probe() )
> > +    {
> > +        hops = &hyperv_ops;
> > +        return true;
> > +    }
> > +#endif
> 
> This recurring #ifdef CONFIG_*_GUEST is going to start looking ugly
> the latest when one or two more get added. Perhaps better providing
> *_probe() stubs returning false, and (like we do elsewhere) rely on
> DCE to get rid of the *_ops reference? (And really you already have
> such a stub - all you need to do is put the hyperv_ops declaration
> outside the #ifdef (but read on).
> 
> Also how about having *_probe() return the address of *_ops, such
> that the latter could all become static?

Previously you made a suggestion to make probe return the name of the
hypervisor. Here you ask for address of ops. I actually prefer the
method suggested here, but this means I will need to keep
hypervisor_name around.

Wei.

> 
> Jan

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