[PATCH 15/17] drm/xe/oa/uapi: OA buffer mmap

[Ashutosh Dixit]

Allow the OA buffer to be mmap'd to userspace. This is needed for the MMIO
trigger use case. Even otherwise, with whitelisted OA head/tail ptr
registers, userspace can receive/interpret OA data from the mmap'd buffer
without issuing read()'s on the OA stream fd.

Suggested-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
---
 drivers/gpu/drm/xe/xe_oa.c | 53 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_oa.c b/drivers/gpu/drm/xe/xe_oa.c
index 42f32d4359f2c..97779cbb83ee8 100644
--- a/drivers/gpu/drm/xe/xe_oa.c
+++ b/drivers/gpu/drm/xe/xe_oa.c
@@ -898,6 +898,8 @@ static int xe_oa_alloc_oa_buffer(struct xe_oa_stream *stream)
 		return PTR_ERR(bo);
 
 	stream->oa_buffer.bo = bo;
+	/* mmap implementation requires OA buffer to be in system memory */
+	xe_assert(stream->oa->xe, bo->vmap.is_iomem == 0);
 	stream->oa_buffer.vaddr = bo->vmap.vaddr;
 	return 0;
 }
@@ -1174,6 +1176,9 @@ static int xe_oa_release(struct inode *inode, struct file *file)
 	struct xe_oa_stream *stream = file->private_data;
 	struct xe_gt *gt = stream->gt;
 
+	/* Zap mmap's */
+	unmap_mapping_range(file->f_mapping, 0, -1, 1);
+
 	mutex_lock(&gt->oa.gt_lock);
 	xe_oa_destroy_locked(stream);
 	mutex_unlock(&gt->oa.gt_lock);
@@ -1184,6 +1189,53 @@ static int xe_oa_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static int xe_oa_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct xe_oa_stream *stream = file->private_data;
+	struct xe_bo *bo = stream->oa_buffer.bo;
+	unsigned long start = vma->vm_start;
+	int i, ret;
+
+	if (xe_perf_stream_paranoid && !perfmon_capable()) {
+		drm_dbg(&stream->oa->xe->drm, "Insufficient privilege to map OA buffer\n");
+		return -EACCES;
+	}
+
+	/* Can mmap the entire OA buffer or nothing (no partial OA buffer mmaps) */
+	if (vma->vm_end - vma->vm_start != XE_OA_BUFFER_SIZE) {
+		drm_dbg(&stream->oa->xe->drm, "Wrong mmap size, must be OA buffer size\n");
+		return -EINVAL;
+	}
+
+	/* Only support VM_READ, enforce MAP_PRIVATE by checking for VM_MAYSHARE */
+	if (vma->vm_flags & (VM_WRITE | VM_EXEC | VM_SHARED | VM_MAYSHARE)) {
+		drm_dbg(&stream->oa->xe->drm, "mmap must be read only\n");
+		return -EINVAL;
+	}
+
+	vm_flags_clear(vma, VM_MAYWRITE | VM_MAYEXEC);
+
+	/*
+	 * If the privileged parent forks and child drops root privilege, we do not want
+	 * the child to retain access to the mapped OA buffer. Explicitly set VM_DONTCOPY
+	 * to avoid such cases.
+	 */
+	vm_flags_set(vma, vma->vm_flags | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_DONTCOPY);
+
+	xe_assert(stream->oa->xe, bo->ttm.ttm->num_pages ==
+		  (vma->vm_end - vma->vm_start) >> PAGE_SHIFT);
+	for (i = 0; i < bo->ttm.ttm->num_pages; i++) {
+		ret = remap_pfn_range(vma, start, page_to_pfn(bo->ttm.ttm->pages[i]),
+				      PAGE_SIZE, vma->vm_page_prot);
+		if (ret)
+			break;
+
+		start += PAGE_SIZE;
+	}
+
+	return ret;
+}
+
 static const struct file_operations xe_oa_fops = {
 	.owner		= THIS_MODULE,
 	.llseek		= no_llseek,
@@ -1191,6 +1243,7 @@ static const struct file_operations xe_oa_fops = {
 	.poll		= xe_oa_poll,
 	.read		= xe_oa_read,
 	.unlocked_ioctl	= xe_oa_ioctl,
+	.mmap		= xe_oa_mmap,
 };
 
 static bool engine_supports_mi_query(struct xe_hw_engine *hwe)
-- 
2.41.0