Re: [PATCH] arm64: Set SSBS for user threads while creation
From: Srinivas Ramana
Date: Tue Dec 24 2019 - 03:30:34 EST
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@xxxxxxxxxxxxxx>
---
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