Re: [PATCH 05/22] x86/srat: vmap the pages for acpi_slit

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 20/12/2022 15:30, Jan Beulich wrote:
> On 16.12.2022 12:48, Julien Grall wrote:
> > From: Hongyan Xia <hongyxia@xxxxxxxxxx>
> >
> > This avoids the assumption that boot pages are in the direct map.
> >
> > Signed-off-by: Hongyan Xia <hongyxia@xxxxxxxxxx>
> > Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> However, ...
>
> > --- a/xen/arch/x86/srat.c
> > +++ b/xen/arch/x86/srat.c
> > @@ -139,7 +139,8 @@ void __init acpi_numa_slit_init(struct acpi_table_slit 
> > *slit)
> >                 return;
> >         }
> >         mfn = alloc_boot_pages(PFN_UP(slit->header.length), 1);
> > -       acpi_slit = mfn_to_virt(mfn_x(mfn));
> > +       acpi_slit = vmap_contig_pages(mfn, PFN_UP(slit->header.length));
> ... with the increased use of vmap space the VA range used will need
> growing. And that's perhaps better done ahead of time than late.
I will have a look to increase the vmap().

> > +       BUG_ON(!acpi_slit);
> Similarly relevant for the earlier patch: It would be nice if boot
> failure for optional things like NUMA data could be avoided.
If you can't map (or allocate the memory), then you are probably in a 
very bad situation because both should really not fail at boot.
So I think this is correct to crash early because the admin will be able 
to look what went wrong. Otherwise, it may be missed in the noise.
>  But I
> understand this is somewhat orthogonal to this series (the more that
> alloc_boot_pages() itself is also affected). Yet not entirely so,
> since previously there was no mapping failure possible here.
See above. I don't see the problem of adding a potential mapping failure 
here and before.
Cheers,

--
Julien Grall