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

[Thomas Gleixner]

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>
> ---
>  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);

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