Re: [PATCH v10 1/2] selftests/vfio: Add NO_SEND_MSI feature flag and MSI helper macros

[David Matlack <dmatlack@google.com>]

On 2026-03-25 02:43 PM, Rubin Du wrote:

> diff --git a/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_driver.h b/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_driver.h
> index e5ada209b1d1..f2cf2608f757 100644
> --- a/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_driver.h
> +++ b/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_driver.h
> @@ -6,6 +6,8 @@
>  
>  struct vfio_pci_device;
>  
> +#define VFIO_PCI_DRIVER_F_NO_SEND_MSI	(1UL << 0) /* Device cannot trigger MSI */

I don't see any particular reason to add this flag. All of the checks
for...

  device->driver.feature & VFIO_PCI_DRIVER_F_NO_SEND_MSI

can just be rewritten as...

  !device->driver.ops->send_msi

to accomplish the same thing. And the latter is less characters while
still being readable.

> -void vfio_pci_driver_send_msi(struct vfio_pci_device *device)
> +int vfio_pci_driver_send_msi(struct vfio_pci_device *device)
>  {
>  	struct vfio_pci_driver *driver = &device->driver;
>  
> +	if (driver->features & VFIO_PCI_DRIVER_F_NO_SEND_MSI)
> +		return -EOPNOTSUPP;
> +

I think it would be better to just let vfio_pci_driver_send_msi() fail
if send_msi() is NULL.

Tests should not be calling vfio_pci_driver_send_msi() if the driver
does not support send_msi(). Tests that require send_msi() should
explicitly check for it, rather than detect it by trying to send an MSI.

It's also more readable to explicitly check for send_msi() support
rather than silently skipping or exiting if send_msi() returns an error.
The latter reads like it could be due to some problem on the device,
rather than just a lack of support in the driver.

> -#define ASSERT_NO_MSI(_eventfd) do {			\
> -	u64 __value;					\
> -							\
> -	ASSERT_EQ(-1, read(_eventfd, &__value, 8));	\
> -	ASSERT_EQ(EAGAIN, errno);			\
> +#define fcntl_set_msi_nonblock(_self) do {				\
> +	if (!(_self->device->driver.features & VFIO_PCI_DRIVER_F_NO_SEND_MSI)) \
> +		fcntl_set_nonblock(_self->msi_fd);			\
> +} while (0)

I think it may be worthwhile to have the nv_falcon driver still enable
at least one MSI or MSI-x vector on the device and set driver->msi. This
will reduce divergence from other drivers, and simplify this commit down
to just:

diff --git a/tools/testing/selftests/vfio/vfio_pci_driver_test.c b/tools/testing/selftests/vfio/vfio_pci_driver_test.c
index afa0480ddd9b..ebd66d677abb 100644
--- a/tools/testing/selftests/vfio/vfio_pci_driver_test.c
+++ b/tools/testing/selftests/vfio/vfio_pci_driver_test.c
@@ -175,6 +175,9 @@ TEST_F(vfio_pci_driver_test, send_msi)
 {
        u64 value;

+       if (!self->device->driver.ops->send_msi)
+               SKIP(return, "Driver does not support send_msi()");
+
        vfio_pci_driver_send_msi(self->device);
        ASSERT_EQ(8, read(self->msi_fd, &value, 8));
        ASSERT_EQ(1, value);
@@ -201,6 +204,9 @@ TEST_F(vfio_pci_driver_test, mix_and_match)
                                       self->dst_iova,
                                       self->size);

+               if (!self->device->driver.ops->send_msi)
+                       continue;
+
                vfio_pci_driver_send_msi(self->device);
                ASSERT_EQ(8, read(self->msi_fd, &value, 8));
                ASSERT_EQ(1, value);

>  TEST_F(vfio_pci_driver_test, send_msi)
>  {
>  	u64 value;
>  
> -	vfio_pci_driver_send_msi(self->device);
> +	if (vfio_pci_driver_send_msi(self->device))
> +		SKIP(return, "Device does not support MSI\n");

NV GPUs do support MSI/x though, right? This should probably be:

  SKIP(return, "Driver does not support send_msi()\n");