From: Will Deacon <will@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: maz@kernel.org, linux-arm-msm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Srinivas Ramana <sramana@codeaurora.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: Set SSBS for user threads while creation
Date: Thu, 9 Jan 2020 15:17:57 +0000 [thread overview]
Message-ID: <20200109151756.GG12236@willie-the-truck> (raw)
In-Reply-To: <20200102180145.GE27940@arrakis.emea.arm.com>
On Thu, Jan 02, 2020 at 06:01:45PM +0000, Catalin Marinas wrote:
> 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 <sramana@codeaurora.org>
>
> 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().
Right, I'd expect the parent SSBS to be inherited when we copy the pstate
field along with the other regs, and I think this is the correct behaviour.
Is that broken somehow?
Will
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next prev parent reply other threads:[~2020-01-09 15:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-23 13:02 [PATCH] arm64: Set SSBS for user threads while creation Srinivas Ramana
2019-12-24 7:06 ` Anshuman Khandual
2019-12-24 8:30 ` Srinivas Ramana
2020-01-02 18:01 ` Catalin Marinas
2020-01-09 15:17 ` Will Deacon [this message]
2020-01-29 11:48 ` Srinivas Ramana
2020-01-29 16:13 ` Will Deacon
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