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

[Farhan Ali]

On 6/22/2026 11:54 AM, Niklas Schnelle wrote:
> On Mon, 2026-06-22 at 10:18 -0700, 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
> SpellingL "it's"
>
> > restored state of device may not have the Memory bit enabled, even if a
> Missing "a" in "of a device"

Ah I missed correcting these.


> > 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.
> The official spec term is "Memory Space Enable" and I think "can lead
> to" is actually underselling it, as the PCIe spec says that accesses
> are "caused to be handled as Unsupported Requests". Also as I
> understand you did see this in practice. Maybe we even want a Fixes
> tag?

This behavior has been present since 41017f0cac92 ("[PATCH] PCI: MSI(X) 
save/restore for suspend/resume"), so I am not sure a fixes tag makes sense?


> > Signed-off-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
> > ---
> >   drivers/pci/msi/msi.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
> > index 81d24a270a79..46a0d9f68a57 100644
> > --- a/drivers/pci/msi/msi.c
> > +++ b/drivers/pci/msi/msi.c
> > @@ -874,6 +874,7 @@ void __pci_restore_msix_state(struct pci_dev *dev)
> >   {
> >   	struct msi_desc *entry;
> >   	bool write_msg;
> > +	u16 cmd;
> >   
> >   	if (!dev->msix_enabled)
> >   		return;
> > @@ -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);
> >   
> >   	write_msg = arch_restore_msi_irqs(dev);
> >   
> > @@ -893,6 +896,7 @@ void __pci_restore_msix_state(struct pci_dev *dev)
> >   		}
> >   	}
> >   
> > +	pci_write_config_word(dev, PCI_COMMAND, cmd);
> >   	pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_MASKALL, 0);
> >   }
> >   
> Code wise this all looks good to me so feel free to add.
>
> Reviewed-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
>
> Thanks,
> Niklas

Thanks for reviewing!

Thanks

Farhan