Re: [Xen-devel] [PATCH] xen: Introduce 'xen_nopv' to disable PV extensions for HVM guests.

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/08/2014 02:47 PM, Konrad Rzeszutek Wilk wrote:
> On Tue, Jul 08, 2014 at 02:22:48PM -0400, Boris Ostrovsky wrote:
> > On 07/08/2014 02:48 PM, konrad@xxxxxxxxxx wrote:
> > > From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > >
> > > By default when CONFIG_XEN and CONFIG_XEN_PVHVM kernels are
> > > run, they will enable the PV extensions (drivers, interrupts, timers,
> > > etc) - which is perfect.
> > >
> > > However, in some cases (kexec not fully wokring, benchmarking)
> > > we want to disable Xen PV extensions. As such introduce the
> > > 'xen_nopv' parameter that will do it.
> > >
> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > ---
> > >   Documentation/kernel-parameters.txt |    4 ++++
> > >   arch/x86/xen/enlighten.c            |   14 ++++++++++++++
> > >   2 files changed, 18 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/Documentation/kernel-parameters.txt 
> > > b/Documentation/kernel-parameters.txt
> > > index c1b9aa8..5dcfa6e 100644
> > > --- a/Documentation/kernel-parameters.txt
> > > +++ b/Documentation/kernel-parameters.txt
> > > @@ -3691,6 +3691,10 @@ bytes respectively. Such letter suffixes can also be 
> > > entirely omitted.
> > >                         Disables the ticketlock slowpath using Xen PV
> > >                         optimizations.
> > > +       xen_nopv        [X86,XEN]
> > > +                       Disables the PV optimizations forcing the guest to run
> > > +                       as generic HVM guest with no PV drivers.
> > > +
> > >         xirc2ps_cs=     [NET,PCMCIA]
> > >                         Format:
> > >                         
> > > <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
> > > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > > index e220197..fec8963 100644
> > > --- a/arch/x86/xen/enlighten.c
> > > +++ b/arch/x86/xen/enlighten.c
> > > @@ -1930,10 +1930,21 @@ static void __init xen_hvm_guest_init(void)
> > >   #endif
> > >   }
> > > +static bool off = false;
> > A more descriptive name would be better.
> disable_pv ?
>
> disable?
>
> xen_pvoff ?
>
> ignore_xen ?
How about xen_nopv, to be consistent with the boot option.

-boris


> > -boris
> >
> > > +static __init int xen_parse_nopv(char *arg)
> > > +{
> > > +       off = true;
> > > +       return 0;
> > > +}
> > > +early_param("xen_nopv", xen_parse_nopv);
> > > +
> > >   static uint32_t __init xen_hvm_platform(void)
> > >   {
> > >         uint32_t eax, ebx, ecx, edx, base;
> > > +       if (off)
> > > +               return 0;
> > > +
> > >         if (xen_pv_domain())
> > >                 return 0;
> > > @@ -1953,6 +1964,9 @@ static uint32_t __init xen_hvm_platform(void)
> > >   bool xen_hvm_need_lapic(void)
> > >   {
> > > +       if (off)
> > > +               return false;
> > > +
> > >         if (xen_pv_domain())
> > >                 return false;
> > >         if (!xen_hvm_domain())

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