Hi Leo,
On 22/03/2019 05:23, 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.
>
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> ---
> 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);
> + }
> +
This seems like the wrong place for this fix.
vfio_pci_msi_vector_write() is called every time the guest pokes the MSI
capability, and checks whether the access was on the Mask Bits Register.
If the function doesn't support per-vector masking, then the register
isn't implemented and we shouldn't do anything here.
To fix the problem I think we need to set masked(virt_state) properly at
init time, instead of blindly setting it to true. In fact from the
guest's point of view, MSIs and MSI-X are unmasked (and disabled) at
boot, so you could always set masked(virt_state) to false, but it may be
safer to copy the actual state of the MSI's Mask Bits into virt_state,
since for MSI, it could be non zero. If per-vector masking isn't
supported, then the virt state should be false.
Thanks,
Jean
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