[Qemu-devel] [PATCH] [v2] Remove TARGET_PAGE_SIZE from virtio interface

[Hollis Blanchard <hollisb@us.ibm.com>]

TARGET_PAGE_SIZE should only be used internal to qemu, not in guest/host
interfaces. The virtio frontend code in Linux uses two constants (PFN shift
and vring alignment) for the interface, so update qemu to match.

I've tested this with PowerPC KVM and confirmed that it fixes virtio problems
when using non-TARGET_PAGE_SIZE pages in the guest.

Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
---
Corrects a silly bug in v1.

Paul Brook doesn't like the idea of a generic align() macro, so vring_align()
is correct.
---
 hw/virtio.c |   16 +++++++++++++---
 hw/virtio.h |    6 ++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/hw/virtio.c b/hw/virtio.c
index e4224ab..0134b0b 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -51,6 +51,14 @@
 /* Virtio ABI version, if we increment this, we break the guest driver. */
 #define VIRTIO_PCI_ABI_VERSION           0
 
+/* How many bits to shift physical queue address written to QUEUE_PFN.
+ * 12 is historical, and due to x86 page size. */
+#define VIRTIO_PCI_QUEUE_ADDR_SHIFT    12
+
+/* The alignment to use between consumer and producer parts of vring.
+ * x86 pagesize again. */
+#define VIRTIO_PCI_VRING_ALIGN         4096
+
 /* QEMU doesn't strictly need write barriers since everything runs in
  * lock-step.  We'll leave the calls to wmb() in though to make it obvious for
  * KVM or if kqemu gets SMP support.
@@ -110,7 +118,9 @@ static void virtqueue_init(VirtQueue *vq, target_phys_addr_t pa)
 {
     vq->vring.desc = pa;
     vq->vring.avail = pa + vq->vring.num * sizeof(VRingDesc);
-    vq->vring.used = TARGET_PAGE_ALIGN(vq->vring.avail + offsetof(VRingAvail, ring[vq->vring.num]));
+    vq->vring.used = vring_align(vq->vring.avail +
+                                 offsetof(VRingAvail, ring[vq->vring.num]),
+                                 VIRTIO_PCI_VRING_ALIGN);
 }
 
 static inline uint64_t vring_desc_addr(VirtQueue *vq, int i)
@@ -386,7 +396,7 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
         vdev->features = val;
         break;
     case VIRTIO_PCI_QUEUE_PFN:
-        pa = (ram_addr_t)val << TARGET_PAGE_BITS;
+        pa = (ram_addr_t)val << VIRTIO_PCI_QUEUE_ADDR_SHIFT;
         vdev->vq[vdev->queue_sel].pfn = val;
         if (pa == 0)
             virtio_reset(vdev);
@@ -660,7 +670,7 @@ void virtio_load(VirtIODevice *vdev, QEMUFile *f)
         if (vdev->vq[i].pfn) {
             target_phys_addr_t pa;
 
-            pa = (ram_addr_t)vdev->vq[i].pfn << TARGET_PAGE_BITS;
+            pa = (ram_addr_t)vdev->vq[i].pfn << VIRTIO_PCI_QUEUE_ADDR_SHIFT;
             virtqueue_init(&vdev->vq[i], pa);
         }
     }
diff --git a/hw/virtio.h b/hw/virtio.h
index 1df8f83..ae92ece 100644
--- a/hw/virtio.h
+++ b/hw/virtio.h
@@ -47,6 +47,12 @@
 /* This means don't interrupt guest when buffer consumed. */
 #define VRING_AVAIL_F_NO_INTERRUPT    1
 
+static inline target_phys_addr_t vring_align(target_phys_addr_t addr,
+                                             unsigned long align)
+{
+    return (addr + align - 1) & ~(align - 1);
+}
+
 typedef struct VirtQueue VirtQueue;
 typedef struct VirtIODevice VirtIODevice;
 
-- 
1.5.6.5