From: Tobias Klausmann tobias.klausmann@freenet.de

[ Upstream commit e94c55b8e0a0bbe9a026250cf31e2fa45957d776 ]

Starting with commit f295c8cfec833c2707ff1512da10d65386dde7af ("drm/nouveau: fix dma syncing warning with debugging on.") the following oops occures:

BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 6 PID: 1013 Comm: Xorg.bin Tainted: G E 5.11.0-desktop-rc0+ #2 Hardware name: Acer Aspire VN7-593G/Pluto_KLS, BIOS V1.11 08/01/2018 RIP: 0010:nouveau_bo_sync_for_device+0x40/0xb0 [nouveau] Call Trace: nouveau_bo_validate+0x5d/0x80 [nouveau] nouveau_gem_ioctl_pushbuf+0x662/0x1120 [nouveau] ? nouveau_gem_ioctl_new+0xf0/0xf0 [nouveau] drm_ioctl_kernel+0xa6/0xf0 [drm] drm_ioctl+0x1f4/0x3a0 [drm] ? nouveau_gem_ioctl_new+0xf0/0xf0 [nouveau] nouveau_drm_ioctl+0x50/0xa0 [nouveau] __x64_sys_ioctl+0x7e/0xb0 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae ---[ end trace ccfb1e7f4064374f ]--- RIP: 0010:nouveau_bo_sync_for_device+0x40/0xb0 [nouveau]

The underlying problem is not introduced by the commit, yet it uncovered the underlying issue. The cited commit relies on valid pages. This is not given for due to some bugs. For now, just warn and work around the issue by just ignoring the bad ttm objects. Below is some debug info gathered while debugging this issue:

nouveau 0000:01:00.0: DRM: ttm_dma->num_pages: 2048 nouveau 0000:01:00.0: DRM: ttm_dma->pages is NULL nouveau 0000:01:00.0: DRM: ttm_dma: 00000000e96058e7 nouveau 0000:01:00.0: DRM: ttm_dma->page_flags: nouveau 0000:01:00.0: DRM: ttm_dma: Populated: 1 nouveau 0000:01:00.0: DRM: ttm_dma: No Retry: 0 nouveau 0000:01:00.0: DRM: ttm_dma: SG: 256 nouveau 0000:01:00.0: DRM: ttm_dma: Zero Alloc: 0 nouveau 0000:01:00.0: DRM: ttm_dma: Swapped: 0

Signed-off-by: Tobias Klausmann tobias.klausmann@freenet.de Signed-off-by: Dave Airlie airlied@redhat.com Link: https://patchwork.freedesktop.org/patch/msgid/20210313222159.3346-1-tobias.k... Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/nouveau/nouveau_bo.c | 8 ++++++++ 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c index f1c9a22083be..e05565f284dc 100644 --- a/drivers/gpu/drm/nouveau/nouveau_bo.c +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c @@ -551,6 +551,10 @@ nouveau_bo_sync_for_device(struct nouveau_bo *nvbo)

if (!ttm_dma) return; + if (!ttm_dma->pages) { + NV_DEBUG(drm, "ttm_dma 0x%p: pages NULL\n", ttm_dma); + return; + }

/* Don't waste time looping if the object is coherent */ if (nvbo->force_coherent) @@ -583,6 +587,10 @@ nouveau_bo_sync_for_cpu(struct nouveau_bo *nvbo)

if (!ttm_dma) return; + if (!ttm_dma->pages) { + NV_DEBUG(drm, "ttm_dma 0x%p: pages NULL\n", ttm_dma); + return; + }

/* Don't waste time looping if the object is coherent */ if (nvbo->force_coherent)