[RFC PATCH 1/2] Add a new register offset let interrupt reason available

[john.liuli]

From: Li Liu john.li...@huawei.com

Add a new register offset VIRTIO_MMIO_ISRMEM which help to
estblish a shared memory region between virtio-mmio driver
and qemu with two purposes:

1.Guest virtio-mmio driver can get the interrupt reason.
2.Check irqfd enabled or not to register different irq handler.

Signed-off-by: Li Liu john.li...@huawei.com
---
 drivers/virtio/virtio_mmio.c |   21 -
 include/linux/virtio_mmio.h  |3 +++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index ef9a165..28ddb55 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -122,6 +122,8 @@ struct virtio_mmio_device {
/* a list of queues so we can dispatch IRQs */
spinlock_t lock;
struct list_head virtqueues;
+
+   uint8_t *isr_mem;
 };
 
 struct virtio_mmio_vq_info {
@@ -443,6 +445,7 @@ static int virtio_mmio_probe(struct platform_device *pdev)
struct virtio_mmio_device *vm_dev;
struct resource *mem;
unsigned long magic;
+   int err;
 
mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (!mem)
@@ -481,6 +484,15 @@ static int virtio_mmio_probe(struct platform_device *pdev)
return -ENXIO;
}
 
+   vm_dev-isr_mem = alloc_pages_exact(PAGE_SIZE, GFP_KERNEL|__GFP_ZERO);
+   if (vm_dev-isr_mem == NULL) {
+   dev_err(pdev-dev, Allocate isr memory failed!\n);
+   return -ENOMEM;
+   }
+
+   writel(virt_to_phys(vm_dev-isr_mem),
+  vm_dev-base + VIRTIO_MMIO_ISRMEM);
+
vm_dev-vdev.id.device = readl(vm_dev-base + VIRTIO_MMIO_DEVICE_ID);
vm_dev-vdev.id.vendor = readl(vm_dev-base + VIRTIO_MMIO_VENDOR_ID);
 
@@ -488,13 +500,20 @@ static int virtio_mmio_probe(struct platform_device *pdev)
 
platform_set_drvdata(pdev, vm_dev);
 
-   return register_virtio_device(vm_dev-vdev);
+   err = register_virtio_device(vm_dev-vdev);
+   if (err) {
+   free_pages_exact(vm_dev-isr_mem, PAGE_SIZE);
+   vm_dev-isr_mem = NULL;
+   }
+
+   return err;
 }
 
 static int virtio_mmio_remove(struct platform_device *pdev)
 {
struct virtio_mmio_device *vm_dev = platform_get_drvdata(pdev);
 
+   free_pages_exact(vm_dev-isr_mem, PAGE_SIZE);
unregister_virtio_device(vm_dev-vdev);
 
return 0;
diff --git a/include/linux/virtio_mmio.h b/include/linux/virtio_mmio.h
index 5c7b6f0..b1e3ec7 100644
--- a/include/linux/virtio_mmio.h
+++ b/include/linux/virtio_mmio.h
@@ -95,6 +95,9 @@
 /* Device status register - Read Write */
 #define VIRTIO_MMIO_STATUS 0x070
 
+/* Allocate ISRMEM for interrupt reason - Write Only */
+#define VIRTIO_MMIO_ISRMEM 0x080
+
 /* The config space is defined by each driver as
  * the per-driver configuration space - Read Write */
 #define VIRTIO_MMIO_CONFIG 0x100
-- 
1.7.9.5


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[RFC PATCH 0/2] virtio-mmio: add irqfd support for vhost-net based on virtio-mmio

[john.liuli]

From: Li Liu john.li...@huawei.com

This set of patches try to implemet irqfd support of vhost-net 
based on virtio-mmio.

I had posted a mail to talking about the status of vhost-net 
on kvm-arm refer to http://www.spinics.net/lists/kvm-arm/msg10804.html.
Some dependent patches are listed in the mail too. Basically the 
vhost-net brings great performance improvements, almost 50%+.

It's easy to implement irqfd support with PCI MSI-X. But till 
now arm32 do not provide equivalent mechanism to let a device 
allocate multiple interrupts. And even the aarch64 provid LPI
but also not available in a short time.

As Gauguey Remy said Vhost does not emulate a complete virtio 
adapter but only manage virtqueue operations. Vhost module
don't update the ISR register, so if with only one irq then it's 
no way to get the interrupt reason even we can inject the 
irq correctly.  

To get the interrupt reason to support such VIRTIO_NET_F_STATUS 
features I add a new register offset VIRTIO_MMIO_ISRMEM which 
will help to establish a shared memory region between qemu and 
virtio-mmio device. Then the interrupt reason can be accessed by
guest driver through this region. At the same time, the virtio-mmio 
dirver check this region to see irqfd is supported or not during 
the irq handler registration, and different handler will be assigned.

I want to know it's the right direction? Does it comply with the 
virtio-mmio spec.? Or anyone have more good ideas to emulate mis-x 
based on virtio-mmio? I hope to get feedback and guidance.
Thx for any help.

Li Liu (2):
  Add a new register offset let interrupt reason available
  Assign a new irq handler while irqfd enabled

 drivers/virtio/virtio_mmio.c |   55 +++---
 include/linux/virtio_mmio.h  |3 +++
 2 files changed, 55 insertions(+), 3 deletions(-)

-- 
1.7.9.5


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[RFC PATCH 2/2] Assign a new irq handler while irqfd enabled

[john.liuli]

From: Li Liu john.li...@huawei.com

This irq handler will get the interrupt reason from a
shared memory. And will be assigned only while irqfd
enabled.

Signed-off-by: Li Liu john.li...@huawei.com
---
 drivers/virtio/virtio_mmio.c |   34 --
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 28ddb55..7229605 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -259,7 +259,31 @@ static irqreturn_t vm_interrupt(int irq, void *opaque)
return ret;
 }
 
+/* Notify all virtqueues on an interrupt. */
+static irqreturn_t vm_interrupt_irqfd(int irq, void *opaque)
+{
+   struct virtio_mmio_device *vm_dev = opaque;
+   struct virtio_mmio_vq_info *info;
+   unsigned long status;
+   unsigned long flags;
+   irqreturn_t ret = IRQ_NONE;
 
+   /* Read the interrupt reason and reset it */
+   status = *vm_dev-isr_mem;
+   *vm_dev-isr_mem = 0x0;
+
+   if (unlikely(status  VIRTIO_MMIO_INT_CONFIG)) {
+   virtio_config_changed(vm_dev-vdev);
+   ret = IRQ_HANDLED;
+   }
+
+   spin_lock_irqsave(vm_dev-lock, flags);
+   list_for_each_entry(info, vm_dev-virtqueues, node)
+   ret |= vring_interrupt(irq, info-vq);
+   spin_unlock_irqrestore(vm_dev-lock, flags);
+
+   return ret;
+}
 
 static void vm_del_vq(struct virtqueue *vq)
 {
@@ -391,6 +415,7 @@ error_available:
return ERR_PTR(err);
 }
 
+#define VIRTIO_MMIO_F_IRQFD(1  7)
 static int vm_find_vqs(struct virtio_device *vdev, unsigned nvqs,
   struct virtqueue *vqs[],
   vq_callback_t *callbacks[],
@@ -400,8 +425,13 @@ static int vm_find_vqs(struct virtio_device *vdev, 
unsigned nvqs,
unsigned int irq = platform_get_irq(vm_dev-pdev, 0);
int i, err;
 
-   err = request_irq(irq, vm_interrupt, IRQF_SHARED,
-   dev_name(vdev-dev), vm_dev);
+   if (*vm_dev-isr_mem  VIRTIO_MMIO_F_IRQFD) {
+   err = request_irq(irq, vm_interrupt_irqfd, IRQF_SHARED,
+ dev_name(vdev-dev), vm_dev);
+   } else {
+   err = request_irq(irq, vm_interrupt, IRQF_SHARED,
+ dev_name(vdev-dev), vm_dev);
+   }
if (err)
return err;
 
-- 
1.7.9.5


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