Re: [PATCH] PCI/MSI: Fix masking MSI/MSI-X on Xen PV

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Sun, Oct 24, 2021 at 9:26 PM Jason Andryuk <jandryuk@xxxxxxxxx> wrote:
>
> commit fcacdfbef5a1 ("PCI/MSI: Provide a new set of mask and unmask
> functions") introduce functions pci_msi_update_mask() and
> pci_msix_write_vector_ctrl() that is missing checks for
> pci_msi_ignore_mask that exists in commit 446a98b19fd6 ("PCI/MSI: Use
> new mask/unmask functions").  The checks are in place at the high level
> __pci_msi_mask_desc()/__pci_msi_unmask_desc(), but some functions call
> directly to the helpers.
>
> Push the pci_msi_ignore_mask check down to the functions that make
> the actual writes.  This keeps the logic local to the writes that need
> to be bypassed.
>
> With Xen PV, the hypervisor is responsible for masking and unmasking the
> interrupts, which pci_msi_ignore_mask is used to indicate.
>
> This change avoids lockups in amdgpu drivers under Xen during boot.
>
> Fixes: commit 446a98b19fd6 ("PCI/MSI: Use new mask/unmask functions")
> Reported-by: Josef Johansson <josef@xxxxxxxxxxx>
> Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> ---

I should have written that this is untested.  If this is the desired
approach, Josef should test that it solves his boot hangs.

Regards,
Jason