Unverified Commit 9c088a5c authored by Arnd Bergmann's avatar Arnd Bergmann Committed by Rodrigo Vivi
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drm/xe: fix devcoredump chunk alignmnent calculation 



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.

v2:
 - Always call div_u64_rem (Matt)

Reported-by: default avatarkernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202504251238.JsNgFeFc-lkp@intel.com/


Fixes: c4a2e5f8 ("drm/xe: Add devcoredump chunking")
Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarMatthew Brost <matthew.brost@intel.com>
Reviewed-by: default avatarRodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20250501012545.1045247-1-matthew.brost@intel.com


Signed-off-by: default avatarRodrigo Vivi <rodrigo.vivi@intel.com>
parent dba7d17d

drivers/gpu/drm/xe/xe_devcoredump.c

+9 −4
Original line number Diff line number Diff line
@@ -177,6 +177,8 @@ 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;

	ssize_t new_chunk_position;



	if (!coredump)

		return -ENODEV;
@@ -201,10 +203,14 @@ static ssize_t xe_devcoredump_read(char *buffer, loff_t offset, 
		return 0;

	}



	new_chunk_position = div_u64_rem(offset,

					 XE_DEVCOREDUMP_CHUNK_MAX,

					 &chunk_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 = new_chunk_position *

			XE_DEVCOREDUMP_CHUNK_MAX;



		__xe_devcoredump_read(ss->read.buffer,

				      XE_DEVCOREDUMP_CHUNK_MAX,
@@ -213,8 +219,7 @@ 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);



	mutex_unlock(&coredump->lock);