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Re: Config space access to Mediatek MT7922 doesn't work after device reset in Xen PV dom0 (regression, Linux 6.12)
- To: Bjorn Helgaas <helgaas@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 29 Jan 2025 14:52:33 +0100
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- Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>, Jürgen Groß <jgross@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, regressions@xxxxxxxxxxxxxxx, Felix Fietkau <nbd@xxxxxxxx>, Lorenzo Bianconi <lorenzo@xxxxxxxxxx>, Ryder Lee <ryder.lee@xxxxxxxxxxxx>, linux-pci@xxxxxxxxxxxxxxx, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 29 Jan 2025 13:52:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 29.01.2025 14:32, Bjorn Helgaas wrote:
> On Wed, Jan 29, 2025 at 04:47:28AM +0100, Marek Marczykowski-Górecki wrote:
>> On Tue, Jan 28, 2025 at 09:40:18PM -0600, Bjorn Helgaas wrote:
>>> I guess the code at [2] is running in user mode and uses Linux
>>> syscalls for config access? Is it straceable?
>>
>> Nope, it's running as the hypervisor and mediates Linux's access to the
>> hardware. In fact, Linux PV kernel (which dom0 is by default under Xen)
>> is running in ring 3...
>>
>> But I can add some more logging there.
>
> So I guess the hypervisor performs the config access on behalf of the
> Linux PV kernel? Obviously Linux thinks CRS/RRS SV is enabled, but I
> suppose all the lspci output is similarly based on whatever the
> hypervisor does, so how do we know the actual hardware config?
The hypervisor only intercepts config space writes; reads, particularly
when going via mmcfg, ought to be unaffected, and hence what lspci shows
should be "the actual hardware config".
Jan
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