[patch 00/18] entry: Consolidate and rework syscall entry handling

[Magnus Lindholm]

>
> With that all architectures using the generic syscall entry code follow the
> same scheme, apply stack randomization at the correct and earliest possible
> place and skip syscall processing depending on the boolean return value of
> syscall_enter_from_user_mode[_work]().
>
> There should be no functional changes, at least there are none intended.
>
> The resulting text size for the syscall entry code on x8664 is slightly
> smaller than before these changes.
>
> Testing syscall heavy workloads and micro benchmarks shows a small
> performance gain for the general rework, but the last patch, which changes
> the logic to be more understandable has no measurable impact in either
> direction.
>
> The series applies on Linus tree and is also available from git:
>
>         git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git entry-rework-v1
>

Hi Thomas,

I did another round of testing of this series on Alpha, this time with my
Alpha GENERIC_ENTRY conversion rebased on top of this series.

For this test I also manually applied the seccomp fixup discussed earlier in
this thread, i.e. fixing the recheck-after-trace logic in
__seccomp_filter() along the lines suggested by Jinjie/Oleg.

With that in place, the kernel boots on Alpha and I do not see any
regressions in the seccomp_bpf kernel selftest or in the strace testsuite.

One note: the seccomp_bpf selftest run on Alpha uses this not-yet-upstream
Alpha selftest enablement patch:

https://lore.kernel.org/linux-alpha/20260203063357.14320-1-linmag7@gmail.com/

One Alpha-specific wrinkle I hit while rebasing the GENERIC_ENTRY patch is
that Alpha cannot unconditionally pre-seed the normal -ENOSYS return state
before calling into the generic entry code: syscall_set_return_value() also
updates r19/a3, which is still syscall argument 4 on the normal entry path.
Doing that too early broke early userspace mmap() during boot.

The Alpha conversion therefore handles this on the no-dispatch path instead:
after the generic entry helper returns, if the syscall is not to be invoked
or the resulting syscall number is invalid, Alpha skips the call, preserves
any ptrace/seccomp/BPF-provided return value, and only synthesizes -ENOSYS if
the return state was otherwise unchanged. That was needed for the
TRACE_syscall.ptrace.syscall_faked and syscall_errno seccomp_bpf cases to
pass.

So from the Alpha side, with the seccomp fixup applied:

Tested-by: Magnus Lindholm linmag7 at gmail.com

Are you planning to send a v2 with the seccomp recheck fix and any other
review fixups folded in? Is the intention to route this upstream
during the next merge window?

Thanks,
Magnus