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Re: [PATCH V7 01/11] xen/pci: arm: add stub for is_memory_hole
- To: Oleksandr <olekstysh@xxxxxxxxx>
- From: Rahul Singh <Rahul.Singh@xxxxxxx>
- Date: Wed, 3 Aug 2022 09:29:30 +0000
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- Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 03 Aug 2022 09:29:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH V7 01/11] xen/pci: arm: add stub for is_memory_hole
Hi Oleksandr,
> On 29 Jul 2022, at 5:28 pm, Oleksandr <olekstysh@xxxxxxxxx> wrote:
>
>
> Hello Rahul
>
>
> On 19.07.22 20:42, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>
>> Add a stub for is_memory_hole which is required for PCI passthrough
>> on Arm.
>>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>> ---
>> OT: It looks like the discussion got stuck. As I understand this
>> patch is not immediately needed in the context of current series
>> as PCI passthrough is not enabled on Arm at the moment. So the patch
>> could be added later on, but it is needed to allow PCI passthrough
>> to be built on Arm for those who want to test it.
>>
>> Copy here some context provided by Julien:
>>
>> Here a summary of the discussion (+ some my follow-up thoughts):
>>
>> is_memory_hole() was recently introduced on x86 (see commit 75cc460a1b8c
>> "xen/pci: detect when BARs are not suitably positioned") to check
>> whether the BAR are positioned outside of a valid memory range. This was
>> introduced to work-around quirky firmware.
>>
>> In theory, this could also happen on Arm. In practice, this may not
>> happen but it sounds better to sanity check that the BAR contains
>> "valid" I/O range.
>>
>> On x86, this is implemented by checking the region is not described is
>> in the e820. IIUC, on Arm, the BARs have to be positioned in pre-defined
>> ranges. So I think it would be possible to implement is_memory_hole() by
>> going through the list of hostbridges and check the ranges.
>>
>> But first, I'd like to confirm my understanding with Rahul, and others.
>
>
> May I please ask about your opinion on that?
I agree with Julien we can implement the something similar to is_memory_hole()
for ARM
that will check that the bar is within the bridge ranges.
If you are okay you can discard this patch in next version of the series and I
will push the patch
for review.
Regards,
Rahul
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