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SubjectRe: [PATCH] xen: Introduce 'xen_nopv' to disable PV extensions for HVM guests.
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On Jul 11, 2014 7:14 PM, "H. Peter Anvin" <hpa@zytor.com> wrote:
>
> On 07/11/2014 04:09 PM, Konrad Rzeszutek Wilk wrote:
> >
> > On Jul 11, 2014 6:52 PM, "H. Peter Anvin" <hpa@zytor.com> wrote:
> >>
> >> On 07/11/2014 12:53 PM, konrad@kernel.org wrote:
> >>>
> >>> 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 ffb101e..eb82239 100644
> >>> --- a/arch/x86/xen/enlighten.c
> >>> +++ b/arch/x86/xen/enlighten.c
> >>> @@ -1826,8 +1826,19 @@ static void __init xen_hvm_guest_init(void)
> >>>   xen_hvm_init_mmu_ops();
> >>>   }
> >>>  
> >>> +static bool xen_nopv = false;
> >>> +static __init int xen_parse_nopv(char *arg)
> >>> +{
> >>> +       xen_nopv = true;
> >>> +       return 0;
> >>> +}
> >>> +early_param("xen_nopv", xen_parse_nopv);
> >>> +
> >>>   static uint32_t __init xen_hvm_platform(void)
> >>>   {
> >>> + if (xen_nopv)
> >>> + return 0;
> >>> +
> >>>   if (xen_pv_domain())
> >>>   return 0;
> >>>  
> >>> @@ -1836,6 +1847,8 @@ static uint32_t __init xen_hvm_platform(void)
> >>>  
> >>>   bool xen_hvm_need_lapic(void)
> >>>   {
> >>> + if (xen_nopv)
> >>> + return false;
> >>>   if (xen_pv_domain())
> >>>   return false;
> >>>   if (!xen_hvm_domain())
> >>>
> >>
> >> Any reason to not simply let xen_pv_domain() return false here?
> >
> > It does return false already.
> >
> > Did you mean to collapse them together?
>
> OK, I'm confused.  The description of the option makes it look like it
> could disable things associated with PV domains, but it looks like it
> actually disables things having to do with HVM domains...
>

Thank you for pointing that out. I will update the documentation to be more clear and specific. It is as you surmised only for HVM guest.

The a
> -hpa
>
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