From: Usama Arif <usama.arif@bytedance.com>
To: dwmw2@infradead.org, tglx@linutronix.de, kim.phillips@amd.com,
brgerst@gmail.com
Cc: piotrgorski@cachyos.org, oleksandr@natalenko.name,
arjan@linux.intel.com, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, hpa@zytor.com, x86@kernel.org,
pbonzini@redhat.com, paulmck@kernel.org,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
rcu@vger.kernel.org, mimoja@mimoja.de, hewenliang4@huawei.com,
thomas.lendacky@amd.com, seanjc@google.com,
pmenzel@molgen.mpg.de, fam.zheng@bytedance.com,
punit.agrawal@bytedance.com, simon.evans@bytedance.com,
liangma@liangbit.com, gpiccoli@igalia.com,
David Woodhouse <dwmw@amazon.co.uk>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v17 2/8] cpu/hotplug: Reset task stack state in _cpu_up()
Date: Wed, 29 Mar 2023 12:09:59 +0100 [thread overview]
Message-ID: <8b6eeca2-bc35-6e17-e1e9-27d77565db67@bytedance.com> (raw)
In-Reply-To: <20230328195758.1049469-3-usama.arif@bytedance.com>
On 28/03/2023 20:57, Usama Arif wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
>
> Commit dce1ca0525bf ("sched/scs: Reset task stack state in bringup_cpu()")
> ensured that the shadow call stack was reset and KASAN poisoning removed
> from a CPU's stack each time that CPU is brought up, not just once.
>
> This is not incorrect. However, with parallel bringup, an architecture
> may obtain the idle thread for a new CPU from a pre-bringup stage, by
> calling idle_thread_get() for itself. This would mean that the cleanup
> in bringup_cpu() would be too late.
>
> Move the SCS/KASAN cleanup to the generic _cpu_up() function instead,
> which already ensures that the new CPU's stack is available, purely to
> allow for early failure. This occurs when the CPU to be brought up is
> in the CPUHP_OFFLINE state, which should correctly do the cleanup any
> time the CPU has been taken down to the point where such is needed.
>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> Tested-by: Mark Rutland <mark.rutland@arm.com> [arm64]
Forgot to include my sign-off. Thanks David for pointing it out.
Signed-off-by: Usama Arif <usama.arif@bytedance.com>
> ---
> kernel/cpu.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 6c0a92ca6bb5..43e0a77f21e8 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -591,12 +591,6 @@ static int bringup_cpu(unsigned int cpu)
> struct task_struct *idle = idle_thread_get(cpu);
> int ret;
>
> - /*
> - * Reset stale stack state from the last time this CPU was online.
> - */
> - scs_task_reset(idle);
> - kasan_unpoison_task_stack(idle);
> -
> /*
> * Some architectures have to walk the irq descriptors to
> * setup the vector space for the cpu which comes online.
> @@ -1383,6 +1377,12 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> ret = PTR_ERR(idle);
> goto out;
> }
> +
> + /*
> + * Reset stale stack state from the last time this CPU was online.
> + */
> + scs_task_reset(idle);
> + kasan_unpoison_task_stack(idle);
> }
>
> cpuhp_tasks_frozen = tasks_frozen;
next prev parent reply other threads:[~2023-03-29 11:10 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-28 19:57 [PATCH v17 0/8] Parallel CPU bringup for x86_64 Usama Arif
2023-03-28 19:57 ` [PATCH v17 1/8] cpu/hotplug: Move idle_thread_get() to <linux/smpboot.h> Usama Arif
2023-03-28 19:57 ` [PATCH v17 2/8] cpu/hotplug: Reset task stack state in _cpu_up() Usama Arif
2023-03-29 11:09 ` Usama Arif [this message]
2023-03-28 19:57 ` [PATCH v17 3/8] cpu/hotplug: Add CPUHP_BP_PARALLEL_STARTUP state before CPUHP_BRINGUP_CPU Usama Arif
2023-03-28 19:57 ` [PATCH v17 4/8] x86/smpboot: Split up native_cpu_up into separate phases and document them Usama Arif
2023-03-28 19:57 ` [PATCH v17 5/8] x86/smpboot: Support parallel startup of secondary CPUs Usama Arif
2023-03-28 19:57 ` [PATCH v17 6/8] x86/smpboot: Send INIT/SIPI/SIPI to secondary CPUs in parallel Usama Arif
2023-03-30 16:46 ` Thomas Gleixner
2023-03-30 17:05 ` Borislav Petkov
2023-03-30 18:17 ` Thomas Gleixner
2023-03-31 11:40 ` [External] " Usama Arif
2023-03-28 19:57 ` [PATCH v17 7/8] x86/smpboot: Serialize topology updates for secondary bringup Usama Arif
2023-03-28 19:57 ` [PATCH v17 8/8] x86/smpboot: Allow parallel bringup for SEV-ES Usama Arif
2023-03-28 20:07 ` Borislav Petkov
2023-03-30 0:10 ` Thomas Gleixner
2023-03-30 7:51 ` Borislav Petkov
2023-03-30 8:15 ` Thomas Gleixner
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