Re: [Xen-devel] [PATCH RESEND v2 2/2] xen: enable vnuma for PV guest

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Nov 19, 2013 at 02:35:59PM +0000, David Vrabel wrote:
> On 19/11/13 14:16, Konrad Rzeszutek Wilk wrote:
> > On Tue, Nov 19, 2013 at 11:54:08AM +0000, David Vrabel wrote:
> >> On 18/11/13 21:58, Elena Ufimtseva wrote:
> >>> Enables numa if vnuma topology hypercall is supported and it is domU.
> >> [...]
> >>> --- a/arch/x86/xen/setup.c
> >>> +++ b/arch/x86/xen/setup.c
> >>> @@ -20,6 +20,7 @@
> >>>  #include <asm/numa.h>
> >>>  #include <asm/xen/hypervisor.h>
> >>>  #include <asm/xen/hypercall.h>
> >>> +#include <asm/xen/vnuma.h>
> >>>  
> >>>  #include <xen/xen.h>
> >>>  #include <xen/page.h>
> >>> @@ -598,6 +599,9 @@ void __init xen_arch_setup(void)
> >>>   WARN_ON(xen_set_default_idle());
> >>>   fiddle_vdso();
> >>>  #ifdef CONFIG_NUMA
> >>> - numa_off = 1;
> >>> + if (!xen_initial_domain() && xen_vnuma_supported())
> >>> +         numa_off = 0;
> >>> + else
> >>> +         numa_off = 1;
> >>>  #endif
> >>>  }
> >>
> >> I think this whole #ifdef CONFIG_NUMA can be removed and hence
> >> xen_vnuma_supported() can be removed as well.
> >>
> >> For any PV guest we can call the xen_numa_init() and it will do the
> >> right thing.
> >>
> >> For dom0, the hypercall will either: return something sensible (if in
> >> the future Xen sets something up), or it will error.
> >>
> >> If Xen does not have vnuma support, the hypercall will error.
> >>
> >> In both error cases, the dummy numa node is setup as required.
> > 
> > Incorrect. It will end up calling:
> > 
> >                  if (!numa_init(amd_numa_init))                             
> >      
> > 
> > which will crash dom0 (see 8d54db795 "xen/boot: Disable NUMA for PV 
> > guests.")
> > as that amd_numa_init is called before the dummy node init.
> 
> No it won't.  Any error path after the check for a PV guest will add the
> dummy node and return success, skipping any of the hardware-specific setup.

Duh! I totally missed 'return' at the end of the check!

However, even with that (so the return), that means
this part won't be called:

649         numa_init(dummy_numa_init);                                         
    

Which means there won't be any dummy numa setup?


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