On 13/10/2020 12:58, Chris Wilson wrote:
Quoting Matthew Auld (2020-10-13 12:18:39)As per the ABI batch_len is u32, however if the batch_len is left unset, then the kernel will just assume batch_len is the size of the whole batch object, however since the vma->size is u64, while the batch_len is just u32 we can end up with batch_len = 0 if we are given too large batch object(e.g 1ULL << 32), which doesn't look the intended behaviour and probably leads to explosions on some HW. Testcase: igt/gem_exec_params/larger-than-life-batch Fixes: 0b5372727be3 ("drm/i915/cmdparser: Use cached vmappings")Nah. That's setting exec_len used for dispatch, not for parsing, which is still using i915_gem_execbuffer_parse(engine, &shadow_exec_entry, params->batch->obj, eb, args->batch_start_offset, args->batch_len, drm_is_current_master(file)); (and args->batch_len is straight from userspace and passed onwards) It's right up until 435e8fc059db ("drm/i915: Allow parsing of unsized batches") where we are using the user value of batch_len for allocating the shadow object and parsing. Fixes: 435e8fc059db ("drm/i915: Allow parsing of unsized batches")
On the topic of that patch, why is it looking at args->batch_len(might be zero), even though it looks like it is trying to move the eb->batch_len calculation to before we call eb_use_cmdparser(), so it can use it(the commit message seems to suggest that?), but then it only looks at the args version anyway. I don't get it.
Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c index 4b09bcd70cf4..80c738c72e6e 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c @@ -869,8 +869,13 @@ static int eb_lookup_vmas(struct i915_execbuffer *eb) return -EINVAL; }- if (eb->batch_len == 0)+ if (eb->batch_len == 0) { eb->batch_len = eb->batch->vma->size - eb->batch_start_offset;if (overflows_type(eb->batch->vma->size - eb->batch_start_offset, eb->batch_len)) It should not have caused the cmdparser any trouble though, it should have been quite happy to copy nothing and reject the batch for reaching the end too early (with a very slim chance of a stale MI_BATCH_BUFFER_END to the rescue). intel_gt_get_buffer_pool() looks suspect given a size of 0, it will either give the largest object it has cached or break upon creating/allocating internal pages. In terms of HW fail, only gen2 used the parameter and it has a very limited batch/GTT size. -Chris
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