Re: [PATCH v20 4/4] PCI/MSI: Enable memory decoding before restoring MSI-X messages

[Farhan Ali]

On 6/23/2026 4:28 AM, Niklas Schnelle wrote:
> On Mon, 2026-06-22 at 13:49 -0700, Farhan Ali wrote:
> > On 6/22/2026 1:29 PM, Thomas Gleixner wrote:
> > > On Mon, Jun 22 2026 at 10:18, Farhan Ali wrote:
> > > > The current MSI-X restoration path assumes the Command register Memory bit
> > > > is enabled when writing MSI-X messages. But its possible the last saved and
> > > > restored state of device may not have the Memory bit enabled, even if a
> > > > device driver later enables Memory bit and MSI-X. Attempting to access
> > > > Memory space without Memory bit enabled can lead to Unsupported Request
> > > > (UR) from the device. Fix this by enabling Memory bit and restore
> > > > it afterwards.
> > > >
> > > > Signed-off-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
> > > > ---
> --- 8< ---
> > > > @@ -882,6 +883,8 @@ void __pci_restore_msix_state(struct pci_dev *dev)
> > > >    	pci_intx_for_msi(dev, 0);
> > > >    	pci_msix_clear_and_set_ctrl(dev, 0,
> > > >    				PCI_MSIX_FLAGS_ENABLE | PCI_MSIX_FLAGS_MASKALL);
> > > > +	pci_read_config_word(dev, PCI_COMMAND, &cmd);
> > > > +	pci_write_config_word(dev, PCI_COMMAND, cmd | PCI_COMMAND_MEMORY);
> > > Can we please have a comment there which explains this? Three month down
> > > the road this will results in head scratching otherwise.
> > >
> > > I agree with Niklas that this wants a Fixes and a Cc:stable tag.
> > >
> > > Other than that:
> > >
> > > Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxx>
> > >
> > > Thanks,
> > >
> > >           tglx
> > I can add a comment, how about something like below?
> >
> > "The restored device state may not have Memory decoding enabled in
> > Command register. Since the MSI-X was enabled for the device, enable
> > Memory decoding before restoring MSI-X"
> Missing "the" before "Command register" other than that this sounds
> good to me and I agree with Thomas that a comment makes sense here.
>
> > For the Fixes tag, do you have a suggestion for a commit? This behavior
> > has been present since 41017f0cac92 ("[PATCH] PCI: MSI(X) save/restore
> > for suspend/resume" which introduced these restore functions. So should
> > be Fixes against 41017f0cac92?
> I'm not sure but my guess would be that for suspend/resume this isn't
> an issue since the suspend part would save the state with Memory Space
> enabled. So it wouldn't be broken in this original use-case. I think
> the problem only occurs in case restore is done for error recovery.
> Might it make sense to have the Fixes tag point to a2f1e22390ac
> ("PCI/ERR: Ensure error recoverability at all times") even though that
> only helps to expose the issue?
>
> Thanks,
> Niklas

Yeah, commit a2f1e22390ac ("PCI/ERR: Ensure error recoverability at all 
times") exposes this issue. I am okay if we want Fixes tag to point to 
this change, unless someone objects. I will also add a note in the 
commit message to specify a2f1e22390ac exposes this issue.

Thanks

Farhan