Hi Alex,
On 3/9/24 00:05, Alex Williamson wrote:
> Currently for devices requiring masking at the irqchip for INTx, ie.
> devices without DisINTx support, the IRQ is enabled in request_irq()
> and subsequently disabled as necessary to align with the masked status
> flag. This presents a window where the interrupt could fire between
> these events, resulting in the IRQ incrementing the disable depth twice.
> This would be unrecoverable for a user since the masked flag prevents
> nested enables through vfio.
>
> Instead, invert the logic using IRQF_NO_AUTOEN such that exclusive INTx
> is never auto-enabled, then unmask as required.
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 89e1f7d4c66d ("vfio: Add PCI device driver")
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
> drivers/vfio/pci/vfio_pci_intrs.c | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index 237beac83809..136101179fcb 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -296,8 +296,15 @@ static int vfio_intx_set_signal(struct vfio_pci_core_device *vdev, int fd)
>
> ctx->trigger = trigger;
>
> + /*
> + * Devices without DisINTx support require an exclusive interrupt,
> + * IRQ masking is performed at the IRQ chip. The masked status is
> + * protected by vdev->irqlock. Setup the IRQ without auto-enable and
> + * unmask as necessary below under lock. DisINTx is unmodified by
> + * the IRQ configuration and may therefore use auto-enable.
If I remember correctly the main reason why the
vdev->pci_2_3 path is left unchanged is due to the fact the irq may not be exclusive
and setting IRQF_NO_AUTOEN could be wrong in that case. May be worth to
precise in the commit msg or here? Besides Reviewed-by: Eric Auger
<eric.auger@xxxxxxxxxx> Eric
> + */
> if (!vdev->pci_2_3)
> - irqflags = 0;
> + irqflags = IRQF_NO_AUTOEN;
>
> ret = request_irq(pdev->irq, vfio_intx_handler,
> irqflags, ctx->name, vdev);
> @@ -308,13 +315,9 @@ static int vfio_intx_set_signal(struct vfio_pci_core_device *vdev, int fd)
> return ret;
> }
>
> - /*
> - * INTx disable will stick across the new irq setup,
> - * disable_irq won't.
> - */
> spin_lock_irqsave(&vdev->irqlock, flags);
> - if (!vdev->pci_2_3 && ctx->masked)
> - disable_irq_nosync(pdev->irq);
> + if (!vdev->pci_2_3 && !ctx->masked)
> + enable_irq(pdev->irq);
> spin_unlock_irqrestore(&vdev->irqlock, flags);
>
> return 0;
