Re: [PATCH 14/16] drm/xe/oa/uapi: OA buffer mmap

[Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>]

On Fri, Jan 19, 2024 at 06:00:24PM -0800, Ashutosh Dixit wrote:
>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.
>
>v2: Remove unmap_mapping_range from xe_oa_release (Thomas H)
>    Use vm_flags_mod (Umesh)
>
>Suggested-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
>Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
>---
> drivers/gpu/drm/xe/xe_oa.c | 46 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 46 insertions(+)
>
>diff --git a/drivers/gpu/drm/xe/xe_oa.c b/drivers/gpu/drm/xe/xe_oa.c
>index eed89649daa08..fd34314563dbf 100644
>--- a/drivers/gpu/drm/xe/xe_oa.c
>+++ b/drivers/gpu/drm/xe/xe_oa.c
>@@ -808,6 +808,8 @@ 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;
> }
>@@ -1074,6 +1076,49 @@ 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, don't copy the vma on fork
>+	 */
>+	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_mod(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_DONTCOPY,
>+		     VM_MAYWRITE | VM_MAYEXEC);
>+
>+	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;
>+}

LGTM,

Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>

Thanks,
Umesh
>+
> static const struct file_operations xe_oa_fops = {
> 	.owner		= THIS_MODULE,
> 	.llseek		= no_llseek,
>@@ -1081,6 +1126,7 @@ 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
>