On Tue, Jan 03, 2023 at 12:42:43PM +0200, Juha-Pekka Heikkila wrote: > Hi Drew,
Hi Juha-Pekka, sorry for the late response since I was on vacation. > > this is good find. I went looking where the problem is in and saw what you > probably also saw earlier. > > I was wondering if diff below would be better fix? I assume this would end > up with einval or erange in your case but code flow otherwise would stay as > is while fixing all future callers for same issue: Yes, the function you identify below is where I encountered divide-by-zero errors. If width/height less than 1 is a legitimate use case, then your proposed solution looks like it would be better. It should have no risk of regression in userspace either, which is nice. I tested your patch, and as expected I did not hit the divide-by-zero error, though the test commit was rejected due to a check further along inside skl_update_scaler. Perhaps there is some other configuration which would pass the test commit with a width/height less than 1, but I didn't dig much further. > > diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c > b/drivers/gpu/drm/i915/display/intel_atomic_plane.c > index 10e1fc9d0698..a9948e8d3543 100644 > --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c > +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c > @@ -144,7 +144,7 @@ unsigned int intel_adjusted_rate(const struct drm_rect > *src, > const struct drm_rect *dst, > unsigned int rate) > { > - unsigned int src_w, src_h, dst_w, dst_h; > + unsigned int src_w, src_h, dst_w, dst_h, dst_wh; > > src_w = drm_rect_width(src) >> 16; > src_h = drm_rect_height(src) >> 16; > @@ -155,8 +155,10 @@ unsigned int intel_adjusted_rate(const struct drm_rect > *src, > dst_w = min(src_w, dst_w); > dst_h = min(src_h, dst_h); > > - return DIV_ROUND_UP_ULL(mul_u32_u32(rate, src_w * src_h), > - dst_w * dst_h); > + /* in case src contained only fractional part */ > + dst_wh = max(dst_w * dst_h, (unsigned) 1); > + > + return DIV_ROUND_UP_ULL(mul_u32_u32(rate, src_w * src_h), dst_wh); > } > > unsigned int intel_plane_pixel_rate(const struct intel_crtc_state > *crtc_state, > > > What do you think? I'll in any case come up with some test for this in igt. I see that you've posted your fix to the list already. Adding a test to cover this in IGT also sounds great. Thanks! Breadcrumbs to Juha-Pekka's patch for anyone following this thread: https://patchwork.freedesktop.org/series/112396/ > > /Juha-Pekka > > On 27.12.2022 7.53, Drew Davenport wrote: > > The error message suggests that the height of the src rect must be at > > least 1. Reject source with height of 0. > > > > Signed-off-by: Drew Davenport <ddavenp...@chromium.org> > > > > --- > > I was investigating some divide-by-zero crash reports on ChromeOS which > > pointed to the intel_adjusted_rate function. Further prodding showed > > that I could reproduce this in a simple test program if I made src_h > > some value less than 1 but greater than 0. > > > > This seemed to be a sensible place to check that the source height is at > > least 1. I tried to repro this issue on an amd device I had on hand, and > > the configuration was rejected. > > > > Would it make sense to add a check that source dimensions are at least 1 > > somewhere in core, like in drm_atomic_plane_check? Or is that a valid > > use case on some devices, and thus any such check should be done on a > > per-driver basis? > > > > Thanks. > > > > drivers/gpu/drm/i915/display/skl_universal_plane.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/gpu/drm/i915/display/skl_universal_plane.c > > b/drivers/gpu/drm/i915/display/skl_universal_plane.c > > index 4b79c2d2d6177..9b172a1e90deb 100644 > > --- a/drivers/gpu/drm/i915/display/skl_universal_plane.c > > +++ b/drivers/gpu/drm/i915/display/skl_universal_plane.c > > @@ -1627,7 +1627,7 @@ static int skl_check_main_surface(struct > > intel_plane_state *plane_state) > > u32 offset; > > int ret; > > - if (w > max_width || w < min_width || h > max_height) { > > + if (w > max_width || w < min_width || h > max_height || h < 1) { > > drm_dbg_kms(&dev_priv->drm, > > "requested Y/RGB source size %dx%d outside limits > > (min: %dx1 max: %dx%d)\n", > > w, h, min_width, max_width, max_height); >