drm/i915/gvt: Support BAR0 8-byte reads/writes

GGTT is in BAR0 with 8 bytes aligned. With a qemu patch (commit:
38d49e8c1523d97d2191190d3f7b4ce7a0ab5aa3), VFIO can use 8-byte reads/
writes to access it.

This patch is to support the 8-byte GGTT reads/writes.

Ideally, we would like to support 8-byte reads/writes for the total BAR0.
But it needs more work for handling 8-byte MMIO reads/writes.

This patch can fix the issue caused by partial updating GGTT entry, during
guest booting up.

v3:
- Use intel_vgpu_get_bar_gpa() stead. (Zhenyu)
- Include all the GGTT checking logic in gtt_entry(). (Zhenyu)

v2:
- Limit to GGTT entry. (Zhenyu)
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/kvmgt.c

@@ -733,6 +733,25 @@ static ssize_t intel_vgpu_rw(struct mdev_device *mdev, char *buf,
 	return ret == 0 ? count : ret;
 }
 
+static bool gtt_entry(struct mdev_device *mdev, loff_t *ppos)
+{
+	struct intel_vgpu *vgpu = mdev_get_drvdata(mdev);
+	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
+	struct intel_gvt *gvt = vgpu->gvt;
+	int offset;
+
+	/* Only allow MMIO GGTT entry access */
+	if (index != PCI_BASE_ADDRESS_0)
+		return false;
+
+	offset = (u64)(*ppos & VFIO_PCI_OFFSET_MASK) -
+		intel_vgpu_get_bar_gpa(vgpu, PCI_BASE_ADDRESS_0);
+
+	return (offset >= gvt->device_info.gtt_start_offset &&
+		offset < gvt->device_info.gtt_start_offset + gvt_ggtt_sz(gvt)) ?
+			true : false;
+}
+
 static ssize_t intel_vgpu_read(struct mdev_device *mdev, char __user *buf,
 			size_t count, loff_t *ppos)
 {
@@ -742,7 +761,21 @@ static ssize_t intel_vgpu_read(struct mdev_device *mdev, char __user *buf,
 	while (count) {
 		size_t filled;
 
-		if (count >= 4 && !(*ppos % 4)) {
+		/* Only support GGTT entry 8 bytes read */
+		if (count >= 8 && !(*ppos % 8) &&
+			gtt_entry(mdev, ppos)) {
+			u64 val;
+
+			ret = intel_vgpu_rw(mdev, (char *)&val, sizeof(val),
+					ppos, false);
+			if (ret <= 0)
+				goto read_err;
+
+			if (copy_to_user(buf, &val, sizeof(val)))
+				goto read_err;
+
+			filled = 8;
+		} else if (count >= 4 && !(*ppos % 4)) {
 			u32 val;
 
 			ret = intel_vgpu_rw(mdev, (char *)&val, sizeof(val),
@@ -802,7 +835,21 @@ static ssize_t intel_vgpu_write(struct mdev_device *mdev,
 	while (count) {
 		size_t filled;
 
-		if (count >= 4 && !(*ppos % 4)) {
+		/* Only support GGTT entry 8 bytes write */
+		if (count >= 8 && !(*ppos % 8) &&
+			gtt_entry(mdev, ppos)) {
+			u64 val;
+
+			if (copy_from_user(&val, buf, sizeof(val)))
+				goto write_err;
+
+			ret = intel_vgpu_rw(mdev, (char *)&val, sizeof(val),
+					ppos, true);
+			if (ret <= 0)
+				goto write_err;
+
+			filled = 8;
+		} else if (count >= 4 && !(*ppos % 4)) {
 			u32 val;
 
 			if (copy_from_user(&val, buf, sizeof(val)))