Re: [Xen-devel] [PATCH for-4.10 2/2] xen/arm: p2m: Add more debug in get_page_from_gva

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/11/17 19:34, Julien Grall wrote:
> The function get_page_from_gva is used by copy_*_guest helpers to
> translate a guest virtual address to a machine physical address and take
> reference on the page.
>
> There are a couple of errors path that will return the same value making
> difficult to know the exact error. Add more debug in each error patch
> only for debug-build.
>
> This should help narrowing down the intermittent failure with the
> hypercall GNTTABOP_copy (see [1]).
>
> [1] https://lists.xen.org/archives/html/xen-devel/2017-11/msg00942.html
>
> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>  xen/arch/arm/p2m.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index f6b3d8e421..417609ede2 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1428,16 +1428,29 @@ struct page_info *get_page_from_gva(struct vcpu *v, 
> vaddr_t va,
>      par = gvirt_to_maddr(va, &maddr, flags);
>  
>      if ( par )
> +    {
> +        dprintk(XENLOG_G_DEBUG,
> +                "%pv: gvirt_to_maddr failed va=%#"PRIvaddr" flags=0x%lx 
> par=%#"PRIx64"\n",
> +                v, va, flags, par);

Given the long round-trip time on debugging output, how about trying to
dump the guest and/or second stage table walk?

~Andrew

>          goto err;
> +    }
>  
>      if ( !mfn_valid(maddr_to_mfn(maddr)) )
> +    {
> +        dprintk(XENLOG_G_DEBUG, "%pv: Invalid MFN %#"PRI_mfn"\n",
> +                v, mfn_x(maddr_to_mfn(maddr)));
>          goto err;
> +    }
>  
>      page = mfn_to_page(maddr_to_mfn(maddr));
>      ASSERT(page);
>  
>      if ( unlikely(!get_page(page, d)) )
> +    {
> +        dprintk(XENLOG_G_DEBUG, "%pv: Failing to acquire the MFN 
> %#"PRI_mfn"\n",
> +                v, mfn_x(maddr_to_mfn(maddr)));
>          page = NULL;
> +    }
>  
>  err:
>      if ( !page && p2m->mem_access_enabled )


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