Re: [PATCH] xen/arm: fix SBDF calculation for vPCI MMIO handlers

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>]

Hi, Roger!

On 27.10.21 11:59, Roger Pau Monné wrote:
> On Wed, Oct 27, 2021 at 11:25:33AM +0300, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>
>> While in vPCI MMIO trap handlers for the guest PCI host bridge it is not
>> enough for SBDF translation to simply call VPCI_ECAM_BDF(info->gpa) as
>> the base address may not be aligned in the way that the translation
>> always work.
> I think I've already raised this during review [0]. But this is only a
> problem if you change the current value of GUEST_VPCI_ECAM_BASE
> AFAICT, as the current value has bits [0,27] clear.
Exactly, so we were just lucky not to hit this before
>
> I assume this is a problem for the hardware domain that needs to trap
> random base addresses as present on hardware, but that code hasn't
> been committed yet.
Yes, I am facing this on the real HW when Dom0's access is trapped
and the base is not taken into account. So, I have a patch for the
future upstream which subtracts the relevant base from the gpa,
e.g. either GUEST_VPCI_ECAM_BASE or bridge->cfg->phys_addr
>
> If that's indeed the case, please expand the commit message to contain
> this information.
I can only mention about "the current value of GUEST_VPCI_ECAM_BASE
AFAICT, as the current value has bits [0,27] clear" as of now because
Dom0 traps are not yet there.
>
> Thanks, Roger.
>
> [0] https://lore.kernel.org/xen-devel/YWlnc3b0sj4akUWa@MacBook-Air-de-Roger.local/
Thank you,
Oleksandr

P.S. Sorry I failed to mark this patch as a fix for 4.16 and explain why it is
a good candidate for 4.16 inclusion