Re: [Xen-devel] [PATCH v6] x86/setup: properly update PTEs if src/dst overlaps when relocating Xen image

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.04.18 at 16:28, <daniel.kiper@xxxxxxxxxx> wrote:
> Commit 0d31d16 (x86/setup: do not relocate Xen over current Xen image
> placement) disallowed src/dst images overlaps when relocating Xen image.
> Though it deliberately allowed destination region between __image_base__
> and (__image_base__ + XEN_IMG_OFFSET) overlaps with the end of source
> image. And here is the problem. If anything between __page_tables_start
> and __page_tables_end in source image lands in the overlap then some or
> even all page table entries may not be updated. This usually means boom
> in early boot which will be difficult to the investigate. So, I think
> that we have three choices to fix the issue:
>   - drop XEN_IMG_OFFSET from
>     if ( (end > s) && (end - reloc_size + XEN_IMG_OFFSET >= __pa(_end)) )
>   - add XEN_IMG_OFFSET to xen_phys_start in PFN_DOWN(xen_phys_start)
>     used in loops as one of conditions and replace ">" with ">=",
>   - change PFN_DOWN(xen_phys_start) to PFN_DOWN(xen_remap_end_pfn)
>     proposed in earlier version of this patch.
> 
> This patch implements the second option. This way we still allow source
> and destination partial overlap as described above but PTEs are properly
> updated now.
> 
> Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
and queuing for after 4.11.

One further small suggestion though:

> @@ -1019,6 +1020,15 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>              bootsym(trampoline_xen_phys_start) = e;
>  
>              /*
> +             * All PTEs pointing above that address are not candidates for
> +             * relocation. Due to possibility of partial overlap of the end
> +             * of source image and the beginning of region for destination
> +             * image some PTEs may point to addresses in
> +             * range [e, e + XEN_IMG_OFFSET).
> +             */
> +            pte_update_limit = PFN_DOWN(e + XEN_IMG_OFFSET);

Perhaps better start with "No PTEs pointing above this address are
candidates ..."?

Jan



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