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Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] > > From: Junrui Luo > > The contiguity scan in amdgpu_vm_update_range() rounds num_entries up to > count * AMDGPU_GPU_PAGES_IN_CPU_PAGE, but count is only constrained by > the loop bound when the loop body executes. The guard > num_entries > AMDGPU_GPU_PAGES_IN_CPU_PAGE proves that > tmp = num_entries / AMDGPU_GPU_PAGES_IN_CPU_PAGE is at least 1, while > the initial count of 2 needs tmp >= 2. > > Each iteration consumes a multiple of AMDGPU_GPU_PAGES_IN_CPU_PAGE, so a > mapping whose GPU page count is not a multiple of it eventually reaches > an iteration where num_entries is above AMDGPU_GPU_PAGES_IN_CPU_PAGE but > below twice that. tmp is then 1, the loop body never runs, count keeps > its initial value, and num_entries is rounded up past what the cursor > holds, tripping BUG_ON(size > cur->remaining) in amdgpu_res_next(). > AMDGPU_GEM_VA is DRM_RENDER_ALLOW and amdgpu_vm_verify_parameters() only > requires map_size to be a multiple of AMDGPU_GPU_PAGE_SIZE, so an > unprivileged caller can reach this. On 4K page hosts > AMDGPU_GPU_PAGES_IN_CPU_PAGE is 1, tmp >= 2 always holds, and the bug is > unreachable. > > Clamp the rounded-up value against num_entries, mirroring the min() that > amdgpu_res_first() already applies to cur->size. A contiguous short tail > is then mapped in full, and a non-contiguous one falls back to a single > CPU page so the loop still makes forward progress. > > Fixes: a39f2a8d7066 ("drm/amdgpu: nuke amdgpu_vm_bo_split_mapping v2") > Reported-by: Yuhao Jiang > Assisted-by: Claude:claude-opus-5 > Cc: stable@vger.kernel.org > Signed-off-by: Junrui Luo > --- > Found by code inspection; not tested on hardware. I have no access to a > 64K-page host with an AMD GPU, so the BUG_ON() path was not exercised at > runtime. That check is clearly not correct. The pages_addr must be fully consumed, otherwise we run into major problems later on. We could do something like this instead: if (pages_addr) { ... if (WARN_ON(num_entries % AMDGPU_GPU_PAGES_IN_CPU_PAGE)) return -EINVAL; ... Regards, Christian. > --- > drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c > index dc6a9d7dd0b2..365a1c4a4527 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c > @@ -1193,8 +1193,9 @@ int amdgpu_vm_update_range(struct amdgpu_device *adev, struct amdgpu_vm *vm, > } > if (!contiguous) > count--; > - num_entries = count * > - AMDGPU_GPU_PAGES_IN_CPU_PAGE; > + num_entries = min(count * > + AMDGPU_GPU_PAGES_IN_CPU_PAGE, > + num_entries); > } > > if (!contiguous) { > > -- > 2.51.2 > >