[PATCH v2] drm/amdgpu: don't migrate a dma-buf into VRAM while runtime suspended

[Mike Lothian <mike@fireburn.co.uk>]

amdgpu_dma_buf_map() adds VRAM to the allowed domains for a peer2peer
attachment, so ttm_bo_validate() can migrate the buffer from GTT into
VRAM.  While the exporting device is runtime suspended its SDMA rings
are down and the move fails:

  amdgpu: Move buffer fallback to memcpy unavailable

An importer on a second GPU reaches this holding no runtime PM
reference on the exporter, e.g. a compositor on the APU submitting a
frame that references a buffer exported by an idle dGPU:

  amdgpu_cs_ioctl -> amdgpu_cs_parser_bos -> amdgpu_cs_bo_validate
    -> ttm_bo_validate -> amdgpu_bo_move -> dma_buf_map_attachment
      -> amdgpu_dma_buf_map -> ttm_bo_validate -> amdgpu_bo_move

Only migrate into VRAM while holding the exporter awake.
pm_runtime_get_if_active() takes a reference only when the device is
already active and never resumes it, so it cannot deadlock against the
reservation held across these callbacks.  That deadlock is why
commit 030631e97b20 ("drm/amdgpu: revert "take runtime pm reference
when we attach a buffer" v2") removed the pm_runtime_get_sync() from
the attach callback.

If the device is suspended or suspending the buffer stays in GTT, which
remains accessible while the GPU is powered down.  A negative return
means runtime PM is disabled, so the device cannot suspend and VRAM
stays usable.

Fixes: 030631e97b20 ("drm/amdgpu: revert "take runtime pm reference when we attach a buffer" v2")
Cc: stable@vger.kernel.org
Signed-off-by: Mike Lothian <mike@fireburn.co.uk>
Assisted-by: Claude:Opus-5 [Claude Code]
---

v2: hold the exporter with pm_runtime_get_if_active() across the
    validate instead of testing adev->mman.buffer_funcs_enabled.  The
    v1 check was racy - the device could suspend between the test and
    ttm_bo_validate(), so amdgpu_bo_move() could still see the rings
    torn down.  Reported by Sashiko AI review.

Is this the failure that commit c52feb436539 ("drm/amdgpu: Disable
runtime PM for externally attached dGPUs") was working around?  That
commit explains how to detect external attachment but not what breaks,
so I can't tell which.

If it is the same thing, could the pci_is_thunderbolt_attached() ||
dev_is_removable() check there be narrowed or dropped on top of this,
so eGPU users keep runtime PM?

I can't test that here: this box hits the bug by missing that check.
The dGPU is on an oculink port off a native AMD root port, so
pci_is_thunderbolt_attached() is false, dev_is_removable() is empty,
and runtime PM stays enabled.

Reproduced on a HawkPoint APU [1002:1900] driving the display with a
Navi 48 [Radeon AI PRO R9700] [1002:7551] on oculink for render
offload.  Without the patch kwin_wayland hits the call chain above
within a minute of the dGPU autosuspending and the desktop stops
repainting until it resumes.

 drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
index b33c300e26e2..c89846f266d3 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
@@ -43,6 +43,7 @@
 #include <linux/dma-buf.h>
 #include <linux/dma-fence-array.h>
 #include <linux/pci-p2pdma.h>
+#include <linux/pm_runtime.h>
 
 static const struct dma_buf_attach_ops amdgpu_dma_buf_attach_ops;
 
@@ -189,14 +190,25 @@ static struct sg_table *amdgpu_dma_buf_map(struct dma_buf_attachment *attach,
 		/* move buffer into GTT or VRAM */
 		struct ttm_operation_ctx ctx = { false, false };
 		unsigned int domains = AMDGPU_GEM_DOMAIN_GTT;
+		int pm_ref = 0;
 
 		if (bo->preferred_domains & AMDGPU_GEM_DOMAIN_VRAM &&
 		    attach->peer2peer) {
-			bo->flags |= AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
-			domains |= AMDGPU_GEM_DOMAIN_VRAM;
+			/*
+			 * Only migrate into VRAM while the exporter is held
+			 * awake.  A negative return means runtime PM is
+			 * disabled, so it cannot suspend either.
+			 */
+			pm_ref = pm_runtime_get_if_active(adev_to_drm(adev)->dev);
+			if (pm_ref) {
+				bo->flags |= AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
+				domains |= AMDGPU_GEM_DOMAIN_VRAM;
+			}
 		}
 		amdgpu_bo_placement_from_domain(bo, domains);
 		r = ttm_bo_validate(&bo->tbo, &bo->placement, &ctx);
+		if (pm_ref > 0)
+			pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
 		if (r)
 			return ERR_PTR(r);
 	}
-- 
2.55.0