linux-kernel - Re: [PATCH v2 0/2] Fix xdp_adjust_frags_tail

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Message-ID: <Z8+8xoSUri3u6+JB@linux.ibm.com>
Date: Tue, 11 Mar 2025 10:02:06 +0530
From: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
To: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        ast@...nel.org, hbathini@...ux.ibm.com, andrii@...nel.org,
        aleksander.lobakin@...el.com, daniel@...earbox.net,
        davem@...emloft.net, kuba@...nel.org, hawk@...nel.org,
        martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
        yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org
Subject: Re: [PATCH v2 0/2] Fix xdp_adjust_frags_tail_grow selftest on powerpc

On Fri, Mar 07, 2025 at 08:54:00PM +0530, Venkat Rao Bagalkote wrote:
> 
> On 05/03/25 10:43 pm, Saket Kumar Bhaskar wrote:
> > For platforms on powerpc architecture with a default page size greater
> > than 4096, there was an inconsistency in fragment size calculation.
> > This caused the BPF selftest xdp_adjust_tail/xdp_adjust_frags_tail_grow
> > to fail on powerpc.
> > 
> > The issue occurred because the fragment buffer size in
> > bpf_prog_test_run_xdp() was set to 4096, while the actual data size in
> > the fragment within the shared skb was checked against PAGE_SIZE
> > (65536 on powerpc) in min_t, causing it to exceed 4096 and be set
> > accordingly. This discrepancy led to an overflow when
> > bpf_xdp_frags_increase_tail() checked for tailroom, as skb_frag_size(frag)
> > could be greater than rxq->frag_size (when PAGE_SIZE > 4096).
> > 
> > This change fixes:
> > 
> > 1. test_run by getting the correct arch dependent PAGE_SIZE.
> > 2. selftest by caculating tailroom and getting correct PAGE_SIZE.
> > 
> > Changes:
> > v1 -> v2:
> >     * Address comments from Alexander
> >        * Use dynamic page size, cacheline size and size of
> >          struct skb_shared_info to calculate parameters.
> >        * Fixed both test_run and selftest.
> > 
> > v1: https://lore.kernel.org/all/20250122183720.1411176-1-skb99@linux.ibm.com/
> > 
> > Saket Kumar Bhaskar (2):
> >    bpf, test_run: Replace hardcoded page size with dynamic PAGE_SIZE in
> >      test_run
> >    selftests/bpf: Refactor xdp_adjust_tail selftest with dynamic sizing
> > 
> >   .../bpf/prog_tests/xdp_adjust_tail.c          | 160 +++++++++++++-----
> >   .../bpf/progs/test_xdp_adjust_tail_grow.c     |  41 +++--
> >   2 files changed, 149 insertions(+), 52 deletions(-)
> > 
> Applied the patch series on the bpf-next and patch works as expected.
> 
> 
> With Out the Patch:
> 
> test_xdp_adjust_frags_tail_grow:PASS:9Kb+10b 0 nsec
> test_xdp_adjust_frags_tail_grow:FAIL:9Kb+10b retval unexpected 9Kb+10b
> retval: actual 3 != expected 1
> test_xdp_adjust_frags_tail_grow:FAIL:9Kb+10b size unexpected 9Kb+10b size:
> actual 13097 != expected 9001
> #583/5   xdp_adjust_tail/xdp_adjust_frags_tail_grow:FAIL
> #583     xdp_adjust_tail:FAIL
> Summary: 0/4 PASSED, 0 SKIPPED, 1 FAILED
> 
> 
> With Patch:
> 
> # ./test_progs -t xdp_adjust_tail
> #583/1   xdp_adjust_tail/xdp_adjust_tail_shrink:OK
> #583/2   xdp_adjust_tail/xdp_adjust_tail_grow:OK
> #583/3   xdp_adjust_tail/xdp_adjust_tail_grow2:OK
> #583/4   xdp_adjust_tail/xdp_adjust_frags_tail_shrink:OK
> #583/5   xdp_adjust_tail/xdp_adjust_frags_tail_grow:OK
> #583     xdp_adjust_tail:OK
> Summary: 1/5 PASSED, 0 SKIPPED, 0 FAILED
> 
> 
> Please add below tag to all the patches in series.
> 
> Tested-by: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
> 
> 
> Regards,
> 
> Venkat.
> 
Thanks for testing this Venkat.

Regards,
Saket