Re: [PATCH] vfio-pci: Fix MSI IRQ forwarding for without per-vector masking

[Leo Yan <leo.yan@linaro.org>]

On Fri, Mar 22, 2019 at 01:23:08PM +0800, Leo Yan wrote:
> If MSI doesn't support per-vector masking capability and
> PCI_MSI_FLAGS_MASKBIT isn't set in message control field, the function
> vfio_pci_msi_vector_write() will directly bail out for this case and
> every vector's 'virt_state' keeps setting bit VFIO_PCI_MSI_STATE_MASKED.
> 
> This results in the state maintained in 'virt_state' cannot really
> reflect the MSI hardware state; finally it will mislead the function
> vfio_pci_update_msi_entry() to skip IRQ forwarding with below flow:
> 
> vfio_pci_update_msi_entry() {
> 
>   [...]
> 
>   if (msi_is_masked(entry->virt_state) == msi_is_masked(entry->phys_state))
>       return 0;  ==> skip IRQ forwarding
> 
>   [...]
> }
> 
> To fix this issue, when detect PCI_MSI_FLAGS_MASKBIT is not set in the
> message control field, this patch simply clears bit
> VFIO_PCI_MSI_STATE_MASKED for all vectors 'virt_state'; at the end
> vfio_pci_update_msi_entry() can forward MSI IRQ successfully.

Just remind, this patch is for kvmtool but not for kernel.  Sorry I
forget to add it in subject.

Thanks,
Leo Yan

> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
>  vfio/pci.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/vfio/pci.c b/vfio/pci.c
> index ba971eb..4fd24ac 100644
> --- a/vfio/pci.c
> +++ b/vfio/pci.c
> @@ -363,8 +363,18 @@ static int vfio_pci_msi_vector_write(struct kvm *kvm, struct vfio_device *vdev,
>  	struct vfio_pci_device *pdev = &vdev->pci;
>  	struct msi_cap_64 *msi_cap_64 = PCI_CAP(&pdev->hdr, pdev->msi.pos);
>  
> -	if (!(msi_cap_64->ctrl & PCI_MSI_FLAGS_MASKBIT))
> +	if (!(msi_cap_64->ctrl & PCI_MSI_FLAGS_MASKBIT)) {
> +		/*
> +		 * If MSI doesn't support per-vector masking capability,
> +		 * simply unmask for all vectors.
> +		 */
> +		for (i = 0; i < pdev->msi.nr_entries; i++) {
> +			entry = &pdev->msi.entries[i];
> +			msi_set_masked(entry->virt_state, false);
> +		}
> +
>  		return 0;
> +	}
>  
>  	if (msi_cap_64->ctrl & PCI_MSI_FLAGS_64BIT)
>  		mask_pos = PCI_MSI_MASK_64;
> -- 
> 2.19.1
>