Re: [PATCH v2] PCI/MSI: Re-add checks for skip masking MSI-X on Xen PV

[Marc Zyngier <maz@xxxxxxxxxx>]

On Tue, 19 Oct 2021 22:48:19 +0100,
Josef Johansson <josef@xxxxxxxxxxx> wrote:
> 
> From: Josef Johansson <josef@xxxxxxxxxxx>
> 
> 
> PCI/MSI: Re-add checks for skip masking MSI-X on Xen PV
>     
> 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"). Add them back since it is
> causing severe lockups in amdgpu drivers under Xen during boot.
> 
> As explained in commit 1a519dc7a73c ("PCI/MSI: Skip masking MSI-X
> on Xen PV"), when running as Xen PV guest, masking MSI-X is a 
> responsibility of the hypervisor.
> 
> Fixes: fcacdfbef5a1 ("PCI/MSI: Provide a new set of mask and unmask
> functions")
> Suggested-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> Signed-off-by: Josef Johansson <josef@xxxxxxxxxxx>
>

[...]

>
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index 0099a00af361..355b791e382f 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -148,6 +148,9 @@ static noinline void pci_msi_update_mask(struct msi_desc 
> *desc, u32 clear, u32 s
>       raw_spinlock_t *lock = &desc->dev->msi_lock;
>       unsigned long flags;
>  
> +     if (pci_msi_ignore_mask || desc->msi_attrib.is_virtual)
> +             return;
> +

I'd rather be consistent, and keep the check outside of
pci_msi_update_mask(), just like we do in __pci_msi_mask_desc().
Something like this instead:

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 0099a00af361..6c69eab304ce 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -420,7 +420,8 @@ static void __pci_restore_msi_state(struct pci_dev *dev)
        arch_restore_msi_irqs(dev);
 
        pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &control);
-       pci_msi_update_mask(entry, 0, 0);
+       if (!(pci_msi_ignore_mask || desc->msi_attrib.is_virtual))
+               pci_msi_update_mask(entry, 0, 0);
        control &= ~PCI_MSI_FLAGS_QSIZE;
        control |= (entry->msi_attrib.multiple << 4) | PCI_MSI_FLAGS_ENABLE;
        pci_write_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, control);

But the commit message talks about MSI-X, and the above is MSI
only. Is Xen messing with the former, the latter, or both?

>       raw_spin_lock_irqsave(lock, flags);
>       desc->msi_mask &= ~clear;
>       desc->msi_mask |= set;
> @@ -181,6 +184,9 @@ static void pci_msix_write_vector_ctrl(struct msi_desc 
> *desc, u32 ctrl)
>  {
>       void __iomem *desc_addr = pci_msix_desc_addr(desc);
>  
> +     if (pci_msi_ignore_mask || desc->msi_attrib.is_virtual)
> +             return;
> +
>       writel(ctrl, desc_addr + PCI_MSIX_ENTRY_VECTOR_CTRL);
>  }

I have similar reservations for this one.

Thanks,

        M.

-- 
Without deviation from the norm, progress is not possible.