Messages in this thread | | | Subject | Re: [PATCH] arm64: Set SSBS for user threads while creation | From | Srinivas Ramana <> | Date | Tue, 24 Dec 2019 14:00:05 +0530 |
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On 12/24/2019 12:36 PM, Anshuman Khandual wrote: > > > On 12/23/2019 06:32 PM, 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. > > So this fixes the situation (i.e low performance) from the creation time > of a task with fork() which will never see a subsequent execve, till it > gets context switched for the very first time ? > Yes, that is correct.
>> >> Fixes: 8f04e8e6e29c ("arm64: ssbd: Add support for PSTATE.SSBS rather than trapping to EL3") >> Signed-off-by: Srinivas Ramana <sramana@codeaurora.org> >> --- >> arch/arm64/kernel/process.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c >> index 71f788cd2b18..a8f05cc39261 100644 >> --- a/arch/arm64/kernel/process.c >> +++ b/arch/arm64/kernel/process.c >> @@ -399,6 +399,13 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, >> */ >> if (clone_flags & CLONE_SETTLS) >> p->thread.uw.tp_value = childregs->regs[3]; >> + >> + if (arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE) { >> + if (is_compat_thread(task_thread_info(p))) >> + set_compat_ssbs_bit(childregs); >> + else >> + set_ssbs_bit(childregs); >> + } >> } else { >> memset(childregs, 0, sizeof(struct pt_regs)); >> childregs->pstate = PSR_MODE_EL1h; >>
Thanks, -- Srinivas R
-- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
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