Re: [Xen-devel] [PATCH] arm/p2m: Fix regression during domain shutdown with active mem_access

[Julien Grall <julien.grall@xxxxxxx>]

Hi Tamas,

On 24/01/2017 22:10, Tamas K Lengyel wrote:
> The change in commit 438c5fe4f0c introduced a regression for domains where
> mem_acces is or was active. When relinquish_p2m_mapping attempts to clear
> a page where the order is not 0 the following ASSERT is triggered:
>
>     ASSERT(!p2m->mem_access_enabled || page_order == 0);
>
> This regression was unfortunately not caught during testing in preparation
> for the 4.8 release.
>
> As at this point during domain shutdown it is safe to skip mem_access paths
> altogether (pages are being relinquished), this patch flips the
> mem_access_enabled flag to forgo any radix-tree lookups and to avoid
> tripping the ASSERT.
>
> Ideally this fix would be part of Xen 4.8.1.
How about fixing the ASSERT rather than turning-off memaccess crudely?

For instance by whether whether the domain is dying.

Cheers,

> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> ---
>  xen/arch/arm/p2m.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 09ceb378a5..1f0ecc9970 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1376,6 +1376,9 @@ int relinquish_p2m_mapping(struct domain *d)
>
>      p2m_write_lock(p2m);
>
> +    /* No need for mem_access now */
> +    p2m->mem_access_enabled = false;
> +
>      for ( ; gfn_x(start) < gfn_x(end);
>            start = gfn_next_boundary(start, order) )
>      {
--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel