Re: [Xen-devel] [PATCH 1/3] x86/dom0: Avoid using 1G superpages if shadowing may be necessary

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.11.18 at 16:26, <andrew.cooper3@xxxxxxxxxx> wrote:
> The shadow code doesn't support 1G superpages, and will hand #PF[RSVD] back to
> guests.

So this change is then instead of trying to make shadow code cope?

> --- a/xen/arch/x86/pv/dom0_build.c
> +++ b/xen/arch/x86/pv/dom0_build.c
> @@ -148,7 +148,14 @@ static __init void setup_pv_physmap(struct domain *d, 
> unsigned long pgtbl_pfn,
>          pl3e += l3_table_offset(vphysmap_start);
>          if ( !l3e_get_intpte(*pl3e) )
>          {
> -            if ( cpu_has_page1gb &&
> +            /*
> +             * 1G superpages aren't supported by the shadow code.  Avoid 
> using
> +             * them we are liable to need to start shadowing dom0.  This

I think there's a word missing here - "when" perhaps?

> +             * assumes that there are no circumstances where we will activate
> +             * logdirty mode on dom0.
> +             */
> +            if ( (!IS_ENABLED(CONFIG_SHADOW_PAGING) ||
> +                  !d->arch.pv.check_l1tf) && cpu_has_page1gb &&
>                   !(vphysmap_start & ((1UL << L3_PAGETABLE_SHIFT) - 1)) &&
>                   vphysmap_end >= vphysmap_start + (1UL << 
> L3_PAGETABLE_SHIFT) &&
>                   (page = alloc_domheap_pages(d,

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan



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