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It was reported that Intel PT address filters do not work in Docker
containers. That relates to the use of overlayfs.
overlayfs records the backing file in struct vm_area_struct vm_file,
instead of the user file that the user mmapped. In order for an address
filter to match, it must compare to the user file inode. There is an
existing helper file_user_inode() for that situation.
Use file_user_inode() instead of file_inode() to get the inode for address
filter matching.
Example:
Setup:
# cd /root
# mkdir test ; cd test ; mkdir lower upper work merged
# cp `which cat` lower
# mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merged
# perf record --buildid-mmap -e intel_pt//u --filter 'filter * @ /root/test/merged/cat' -- /root/test/merged/cat /proc/self/maps
...
55d61d246000-55d61d2e1000 r-xp 00018000 00:1a 3418 /root/test/merged/cat
...
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.015 MB perf.data ]
# perf buildid-cache --add /root/test/merged/cat
Before:
Address filter does not match so there are no control flow packets
# perf script --itrace=e
# perf script --itrace=b | wc -l
0
# perf script -D | grep 'TIP.PGE' | wc -l
0
#
After:
Address filter does match so there are control flow packets
# perf script --itrace=e
# perf script --itrace=b | wc -l
235
# perf script -D | grep 'TIP.PGE' | wc -l
57
#
With respect to stable kernels, overlayfs mmap function ovl_mmap() was
added in v4.19 but file_user_inode() was not added until v6.8 and never
back-ported to stable kernels. FMODE_BACKING that it depends on was added
in v6.5. This issue has gone largely unnoticed, so back-porting before
v6.8 is probably not worth it, so put 6.8 as the stable kernel prerequisite
version, although in practice the next long term kernel is 6.12.
Closes: https://lore.kernel.org/linux-perf-users/aBCwoq7w8ohBRQCh@fremen.lan
Reported-by: Edd Barrett <edd@theunixzoo.co.uk>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Amir Goldstein <amir73il@gmail.com>
Cc: stable@vger.kernel.org # 6.8
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.