On Tue, Apr 29, 2025 at 09:34:00AM +0200, Arnd Bergmann wrote: > From: Arnd Bergmann <a...@arndb.de> > > The device core dumps are copied in 1.5GB chunks, which leads to a > link-time error on 32-bit builds because of the 64-bit division not > getting trivially turned into mask and shift operations: > > ERROR: modpost: "__moddi3" [drivers/gpu/drm/xe/xe.ko] undefined! > > On top of this, I noticed that the ALIGN_DOWN() usage here cannot > work because that is only defined for power-of-two alignments. > Change ALIGN_DOWN into an explicit div_u64_rem() that avoids the > link error and hopefully produces the right results. > > Doing a 1.5GB kvmalloc() does seem a bit suspicious as well, e.g. > this will clearly fail on any 32-bit platform and is also likely > to run out of memory on 64-bit systems under memory pressure, so > using a much smaller power-of-two chunk size might be a good idea > instead. > > Fixes: c4a2e5f865b7 ("drm/xe: Add devcoredump chunking") > Signed-off-by: Arnd Bergmann <a...@arndb.de>
Thanks for the fix, I had similar one [1] but I missed issue with ALIGN_DOWN. [1] https://patchwork.freedesktop.org/series/148301/ > --- > Please test this with multi-gigabyte buffers, the original code > was clearly not right, but I don't trust my version either. This was tested on 64-bit only. I do see an issue with this version though. Inline below. > --- > drivers/gpu/drm/xe/xe_devcoredump.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/xe/xe_devcoredump.c > b/drivers/gpu/drm/xe/xe_devcoredump.c > index a9e618abf8ac..4eb70e2d9f68 100644 > --- a/drivers/gpu/drm/xe/xe_devcoredump.c > +++ b/drivers/gpu/drm/xe/xe_devcoredump.c > @@ -177,6 +177,7 @@ static ssize_t xe_devcoredump_read(char *buffer, loff_t > offset, > struct xe_devcoredump *coredump = data; > struct xe_devcoredump_snapshot *ss; > ssize_t byte_copied; > + u32 chunk_offset; > > if (!coredump) > return -ENODEV; > @@ -203,8 +204,9 @@ static ssize_t xe_devcoredump_read(char *buffer, loff_t > offset, > > if (offset >= ss->read.chunk_position + XE_DEVCOREDUMP_CHUNK_MAX || > offset < ss->read.chunk_position) { > - ss->read.chunk_position = > - ALIGN_DOWN(offset, XE_DEVCOREDUMP_CHUNK_MAX); > + ss->read.chunk_position = div_u64_rem(offset, > + XE_DEVCOREDUMP_CHUNK_MAX, &chunk_offset) > + * XE_DEVCOREDUMP_CHUNK_MAX; > > __xe_devcoredump_read(ss->read.buffer, > XE_DEVCOREDUMP_CHUNK_MAX, > @@ -213,8 +215,7 @@ static ssize_t xe_devcoredump_read(char *buffer, loff_t > offset, > > byte_copied = count < ss->read.size - offset ? count : > ss->read.size - offset; > - memcpy(buffer, ss->read.buffer + > - (offset % XE_DEVCOREDUMP_CHUNK_MAX), byte_copied); > + memcpy(buffer, ss->read.buffer + chunk_offset, byte_copied); chunk_offset is unset unless a new devcoredump is read which is every 1.5 GB. You will need always call div_u64_rem outside of the above if statement. Matt > > mutex_unlock(&coredump->lock); > > -- > 2.39.5 >