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

[Julien Grall <julien.grall@linaro.org>]

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@linaro.org>
>> ---
>>   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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