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Re: [PATCH 04/12] swiotlb-xen: ensure to issue well-formed XENMEM_exchange requests

  • To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 14 Sep 2021 11:11:06 +0200
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, lkml <linux-kernel@xxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 14 Sep 2021 09:11:18 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 13.09.2021 22:31, Stefano Stabellini wrote:
> On Mon, 13 Sep 2021, Jan Beulich wrote:
>> On 11.09.2021 01:14, Stefano Stabellini wrote:
>>> On Tue, 7 Sep 2021, Jan Beulich wrote:
>>>> While the hypervisor hasn't been enforcing this, we would still better
>>>> avoid issuing requests with GFNs not aligned to the requested order.
>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>> ---
>>>> I wonder how useful it is to include the alignment in the panic()
>>>> message.
>>> Not very useful given that it is static. I don't mind either way but you
>>> can go ahead and remove it if you prefer (and it would make the line
>>> shorter.)
>>>> I further wonder how useful it is to wrap "bytes" in
>>>> PAGE_ALIGN(), when it is a multiple of a segment's size anyway (or at
>>>> least was supposed to be, prior to "swiotlb-xen: maintain slab count
>>>> properly").
>>> This one I would keep, to make sure to print out the same amount passed
>>> to memblock_alloc.
>> Oh - if I was to drop it from the printk(), I would have been meaning to
>> also drop it there. If it's useless, then it's useless everywhere.
> That's fine too

Thanks, I'll see about dropping that then.

Another Arm-related question has occurred to me: Do you actually
mind the higher-than-necessary alignment there? If so, a per-arch
definition of the needed alignment would need introducing. Maybe
that could default to PAGE_SIZE, allowing Arm and alike to get away
without explicitly specifying a value ...




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