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

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Andrew,

On 11/15/2017 07:43 PM, Andrew Cooper wrote:
> 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?
I thought about it, however at the moment dump_s1_guest_walk() is very 
minimal and would be add much value here. Thought, Now that we have code 
to do first-stage walk (see guest_walk_tables), we might be able to get 
a better dump here. Thought I am not sure it would be 4.10 material.
However, I think we could try to translate the guest VA to a guest PA 
using hardware instruction and then do the second-stage walk using 
dump_p2m_lookup.
Let me have a look.

Cheers,

--
Julien Grall

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