Re: [PATCH 2/3] xen/arm: vgic-v3: Correctly retrieve the vCPU associated to a re-distributor

[Julien Grall <julien.grall@citrix.com>]

On 29/09/15 14:56, Ian Campbell wrote:
> On Mon, 2015-09-28 at 21:31 +0100, Julien Grall wrote:
>> When the guest is accessing the re-distributor, Xen retrieves the base
>> of the re-distributor using a mask based on the stride.
>>
>> Although, when the stride contains multiple set, the corresponding mask
> 
>                                                  ^bits?

I guess you mean "multiple bits set" here?

> (Also, drop the "Although, ").
> 
>> will be computed incorrectly [1] and therefore giving invalid vCPU and
>> offset:
>>
>> (XEN) d0v0: vGICR: unknown gpa read address 000000008d130008
>> (XEN) traps.c:2447:d0v1 HSR=0x93c08006 pc=0xffffffc00032362c
>> gva=0xffffff80000b0008 gpa=0x0000008d130008
>>
>> For instance if the region of re-distributor is starting at 0x8d100000
>> and the stride is 0x30000, an access to the address 0x8d130008 should
>> be valid and use the re-distributor of vCPU1 with an offset of 0x8.
>> Although, Xen is returning the vCPU0 and an offset of 0x20008.
>>
>> I didn't find a way to replace the current computation of the mask with
>> a valid. The only solution I have found is to pass the region in private
> 
>         ^one
> 
>> data of the handler. So we can directly get the offset from the
>> beginning of the region and find the corresponding vCPU/offset in the
>> re-distributor.
>>
>> This is also make the code simpler and avoid fast/slow path.
>>
>> [1] http://lists.xen.org/archives/html/xen-devel/2015-09/msg03372.html
>>
>> Signed-off-by: Julien Grall <julien.grall@citrix.com>
>>
>> ---
>> Cc: shameerali.kolothum.thodi@huawei.com
>> Cc: Wei Liu <wei.liu2@citrix.com>
>>
>>     This is technically a good candidate for Xen 4.6. Without it DOM0
>>     may not be able to bring secondary CPU on platform using a stride
>>     with multiple bit set [1]. Although, we don't support such platform
>>     right now. So I would rather defer this change to Xen 4.6.1 and
>>     avoid possible downside/bug in this patch.
> 
> Agreed.
> 
> Other than the text:
> 
> Acked-by: Ian Campbell <ian.campbell@citrix.com>

Thank you.

Regards,

-- 
Julien Grall