On Mon, Dec 23, 2019 at 06:32:26PM +0530, Srinivas Ramana wrote:

Current SSBS implementation takes care of setting the
SSBS bit in start_thread() for user threads. While this works
for tasks launched with fork/clone followed by execve, for cases
where userspace would just call fork (eg, Java applications) this
leaves the SSBS bit unset. This results in performance
regression for such tasks.

It is understood that commit cbdf8a189a66 ("arm64: Force SSBS
on context switch") masks this issue, but that was done for a
different reason where heterogeneous CPUs(both SSBS supported
and unsupported) are present. It is appropriate to take care
of the SSBS bit for all threads while creation itself.

Fixes: 8f04e8e6e29c ("arm64: ssbd: Add support for PSTATE.SSBS rather than trapping to EL3")
Signed-off-by: Srinivas Ramana <redacted>

I suppose the parent process cleared SSBS explicitly. Isn't the child
after fork() supposed to be nearly identical to the parent? If we did as
you suggest, someone else might complain that SSBS has been set in the
child after fork().

I think the fix is for user space to set SSBS in the child if it no
longer needs it.

-- 
Catalin

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel