Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support

From: Avi Kivity
Date: Mon Oct 05 2015 - 04:28:18 EST


On 10/05/2015 06:11 AM, Greg KH wrote:
On Sun, Oct 04, 2015 at 11:43:17PM +0300, Vlad Zolotarov wrote:
Add support for MSI and MSI-X interrupt modes:
- Interrupt mode selection order is:
INT#X (for backward compatibility) -> MSI-X -> MSI.
- Add ioctl() commands:
- UIO_PCI_GENERIC_INT_MODE_GET: query the current interrupt mode.
- UIO_PCI_GENERIC_IRQ_NUM_GET: query the maximum number of IRQs.
- UIO_PCI_GENERIC_IRQ_SET: bind the IRQ to eventfd (similar to vfio).
- Add mappings to all bars (memory and portio): some devices have
registers related to MSI/MSI-X handling outside BAR0.

Signed-off-by: Vlad Zolotarov <vladz@xxxxxxxxxxxxxxxxxxxx>
---
New in v3:
- Add __iomem qualifier to temp buffer receiving ioremap value.

New in v2:
- Added #include <linux/uaccess.h> to uio_pci_generic.c

Signed-off-by: Vlad Zolotarov <vladz@xxxxxxxxxxxxxxxxxxxx>
---
drivers/uio/uio_pci_generic.c | 410 +++++++++++++++++++++++++++++++++++++---
include/linux/uio_pci_generic.h | 36 ++++
2 files changed, 423 insertions(+), 23 deletions(-)
create mode 100644 include/linux/uio_pci_generic.h

diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
index d0b508b..6b8b1789 100644
--- a/drivers/uio/uio_pci_generic.c
+++ b/drivers/uio/uio_pci_generic.c
@@ -22,16 +22,32 @@
#include <linux/device.h>
#include <linux/module.h>
#include <linux/pci.h>
+#include <linux/msi.h>
#include <linux/slab.h>
#include <linux/uio_driver.h>
+#include <linux/uio_pci_generic.h>
+#include <linux/eventfd.h>
+#include <linux/uaccess.h>
#define DRIVER_VERSION "0.01.0"
#define DRIVER_AUTHOR "Michael S. Tsirkin <mst@xxxxxxxxxx>"
#define DRIVER_DESC "Generic UIO driver for PCI 2.3 devices"
+struct msix_info {
+ int num_irqs;
+ struct msix_entry *table;
+ struct uio_msix_irq_ctx {
+ struct eventfd_ctx *trigger; /* MSI-x vector to eventfd */
Why are you using eventfd for msi vectors? What's the reason for
needing this?

You haven't documented how this api works at all, you are going to have
to a lot more work to justify this, as this greatly increases the
complexity of the user/kernel api in unknown ways.



Of course it has to be documented, but this just follows vfio.

Eventfd is a natural enough representation of an interrupt; both kvm and vfio use it, and are also able to share the eventfd, allowing a vfio interrupt to generate a kvm interrupt, without userspace intervention, and one day without even kernel intervention.

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