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drm/xe: fix devcoredump chunk alignmnent calculation

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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: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202504251238.JsNgFeFc-lkp@intel.com/
Fixes: c4a2e5f865 ("drm/xe: Add devcoredump chunking")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20250501012545.1045247-1-matthew.brost@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
This commit is contained in:
Arnd Bergmann 2025-04-30 18:25:45 -07:00 committed by Rodrigo Vivi
parent dba7d17d50
commit 9c088a5c0d
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GPG Key ID: FA625F640EEB13CA
1 changed files with 9 additions and 4 deletions
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13
drivers/gpu/drm/xe/xe_devcoredump.c
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@ -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);