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Re: [PATCH 6/9] vpci/header: Handle p2m range sets per BAR

  • To: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>, Oleksandr Andrushchenko <andr2000@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 9 Sep 2021 13:51:40 +0200
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  • Cc: "julien@xxxxxxx" <julien@xxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <Oleksandr_Tyshchenko@xxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Artem Mygaiev <Artem_Mygaiev@xxxxxxxx>, "roger.pau@xxxxxxxxxx" <roger.pau@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Rahul Singh <rahul.singh@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 09 Sep 2021 11:51:52 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 09.09.2021 13:30, Oleksandr Andrushchenko wrote:
> On 09.09.21 13:46, Jan Beulich wrote:
>> On 09.09.2021 12:03, Oleksandr Andrushchenko wrote:
>>> On 09.09.21 12:39, Jan Beulich wrote:
>>>> And in fact I wonder whether for DomU-s you want to support BAR changes
>>>> in the first place while memory decoding is enabled.
>>> No, why? I want to keep the existing logic, e.g. with memory decoding
>>> disabled as it is now.
>> Afaict existing code deals with both cases.
> Hm, I thought that we only map/unmap with memory decoding disabled.
> For my education: what happens if you unmap with decoding enabled and
> domain accesses the MMIOs?

That would depend on the precise timing; it's certainly not well defined.
But supporting this may be needed for quirky OSes, as said before, as
they may get away with that on real hardware if they avoid actual accesses
at the time of the BAR change.




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