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List:       kvm
Subject:    Re: [RESEND PATCH v3 2/2] vfio/pci: Restore MSIx message prior to enabling
From:       Alex Williamson <alex.williamson () redhat ! com>
Date:       2014-09-30 0:22:02
Message-ID: 1412036522.7360.125.camel () ul30vt ! home
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On Sat, 2014-09-27 at 15:43 +1000, Gavin Shan wrote:
> The MSIx vector table lives in device memory, which may be cleared as
> part of a backdoor device reset. This is the case on the IBM IPR HBA
> when the BIST is run on the device. When assigned to a QEMU guest,
> the guest driver does a pci_save_state(), issues a BIST, then does a
> pci_restore_state(). The BIST clears the MSIx vector table, but due
> to the way interrupts are configured the pci_restore_state() does not
> restore the vector table as expected. Eventually this results in an
> EEH error on Power platforms when the device attempts to signal an
> interrupt with the zero'd table entry.
> 
> Fix the problem by restoring the host cached MSI message prior to
> enabling each vector.
> 
> Reported-by: Wen Xiong <wenxiong@linux.vnet.ibm.com>
> Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
>  drivers/vfio/pci/vfio_pci_intrs.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)

Applied both to linux-vfio.git/next for 3.18.  Thanks!

Alex

> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index 9dd49c9..553212f 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -16,6 +16,7 @@
>  #include <linux/device.h>
>  #include <linux/interrupt.h>
>  #include <linux/eventfd.h>
> +#include <linux/msi.h>
>  #include <linux/pci.h>
>  #include <linux/file.h>
>  #include <linux/poll.h>
> @@ -548,6 +549,20 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_device *vdev,
>  		return PTR_ERR(trigger);
>  	}
>  
> +	/*
> +	 * The MSIx vector table resides in device memory which may be cleared
> +	 * via backdoor resets. We don't allow direct access to the vector
> +	 * table so even if a userspace driver attempts to save/restore around
> +	 * such a reset it would be unsuccessful. To avoid this, restore the
> +	 * cached value of the message prior to enabling.
> +	 */
> +	if (msix) {
> +		struct msi_msg msg;
> +
> +		get_cached_msi_msg(irq, &msg);
> +		write_msi_msg(irq, &msg);
> +	}
> +
>  	ret = request_irq(irq, vfio_msihandler, 0,
>  			  vdev->ctx[vector].name, trigger);
>  	if (ret) {



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