linux-kernel - Re: Config space access to Mediatek MT7922 doesn't work after device reset in Xen PV dom0 (regression, Linux 6.12)

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Message-ID: <Z5mk0K5xltK6iZXN@mail-itl>
Date: Wed, 29 Jan 2025 04:47:28 +0100
From: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Jürgen Groß <jgross@...e.com>,
	Roger Pau Monné <roger.pau@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	xen-devel <xen-devel@...ts.xenproject.org>,
	linux-kernel@...r.kernel.org, regressions@...ts.linux.dev,
	Felix Fietkau <nbd@....name>, Lorenzo Bianconi <lorenzo@...nel.org>,
	Ryder Lee <ryder.lee@...iatek.com>, linux-pci@...r.kernel.org
Subject: Re: Config space access to Mediatek MT7922 doesn't work after device
 reset in Xen PV dom0 (regression, Linux 6.12)

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.

> Can you reproduce this without Xen at all?  If so, can you post a
> complete dmesg and complete lspci -vv somewhere?

I haven't managed to reproduce it without Xen so far. But I can't
exclude it's some race condition that is simply unlikely to hit when
Linux runs natively. 

> > > [1] https://github.com/QubesOS/qubes-issues/issues/9689#issuecomment-2582927149
> > 
> > [2] https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/pv/emul-priv-op.c;h=70150c27227661baa253af8693ff00f2ab640a98;hb=HEAD#l295
> 
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/probe.c?id=v6.13#n1208

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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