Re: [PATCH 3/6] x86: Add nopv parameter to disable PV extensions

[Zhenzhong Duan]

On 2019/6/24 21:18, Juergen Gross wrote:
> On 23.06.19 15:01, Zhenzhong Duan wrote:
> > In virtualization environment, PV extensions (drivers, interrupts,
> > timers, etc) are enabled in the majority of use cases which is the
> > best option.
> >
> > However, in some cases (kexec not fully working, benchmarking)
> > we want to disable PV extensions. As such introduce the
> > 'nopv' parameter that will do it.
> >
> > There is already 'xen_nopv' parameter for XEN platform but not for
> > others. 'xen_nopv' can then be removed with this change.
> >
> > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> > ---
> > Â Documentation/admin-guide/kernel-parameters.txt |Â 4 ++++
> > Â arch/x86/kernel/cpu/hypervisor.cÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ | 11 +++++++++++
> > Â 2 files changed, 15 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt 
> > b/Documentation/admin-guide/kernel-parameters.txt
> > index 138f666..b352f36 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -5268,6 +5268,10 @@
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ improve timer resolution at the expense of processing
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ more timer interrupts.
> > Â +ÂÂÂ nopv=ÂÂÂÂÂÂÂ [X86]
> > +ÂÂÂÂÂÂÂÂÂÂÂ Disables the PV optimizations forcing the guest to run
> > +ÂÂÂÂÂÂÂÂÂÂÂ as generic guest with no PV drivers.
> > +
> > ÂÂÂÂÂ xirc2ps_cs=ÂÂÂ [NET,PCMCIA]
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ Format:
> > <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
> > diff --git a/arch/x86/kernel/cpu/hypervisor.c 
> > b/arch/x86/kernel/cpu/hypervisor.c
> > index 479ca47..4f2c875 100644
> > --- a/arch/x86/kernel/cpu/hypervisor.c
> > +++ b/arch/x86/kernel/cpu/hypervisor.c
> > @@ -85,10 +85,21 @@ static void __init copy_array(const void *src, 
> > void *target, unsigned int size)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ to[i] = from[i];
> > Â }
> > Â +static bool nopv;
> > +static __init int xen_parse_nopv(char *arg)
> > +{
> > +ÂÂÂ nopv = true;
> > +ÂÂÂ return 0;
> > +}
> > +early_param("nopv", xen_parse_nopv);
> > +
> > Â void __init init_hypervisor_platform(void)
> > Â {
> > ÂÂÂÂÂ const struct hypervisor_x86 *h;
> > Â +ÂÂÂ if (nopv)
> > +ÂÂÂÂÂÂÂ return;
> > +
>
> Oh, this is no good idea.
>
> There are guest types which just won't work without pv interfaces, like
> Xen PV and Xen PVH. Letting them fail due to just a wrong command line
> parameter is not nice, especially as the failure might be very hard to
> track down to the issue for the user.
Yes, thanks for catching.
> I guess you could add a "ignore_nopv" member to struct hypervisor_x86
> set to true for the mentioned guest types and call the detect functions
> only if nopv is false or ignore_nopv is true.

I think your suggestion is good, I'll rework it based on your suggestion.

Thanks

Zhenzhong