From: Peter Zijlstra <peterz@infradead.org> To: Will Deacon <will@kernel.org> Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>, Marc Zyngier <maz@kernel.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Morten Rasmussen <morten.rasmussen@arm.com>, Qais Yousef <qais.yousef@arm.com>, Suren Baghdasaryan <surenb@google.com>, Quentin Perret <qperret@google.com>, Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>, Johannes Weiner <hannes@cmpxchg.org>, Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>, Vincent Guittot <vincent.guittot@linaro.org>, kernel-team@android.com Subject: Re: [PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Date: Thu, 19 Nov 2020 17:42:03 +0100 [thread overview] Message-ID: <20201119164203.GU3121392@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20201119162822.GA4582@willie-the-truck> On Thu, Nov 19, 2020 at 04:28:23PM +0000, Will Deacon wrote: > On Thu, Nov 19, 2020 at 05:14:48PM +0100, Peter Zijlstra wrote: > > On Fri, Nov 13, 2020 at 09:37:13AM +0000, Will Deacon wrote: > > > When exec'ing a 32-bit task on a system with mismatched support for > > > 32-bit EL0, try to ensure that it starts life on a CPU that can actually > > > run it. > > > > > > Signed-off-by: Will Deacon <will@kernel.org> > > > --- > > > arch/arm64/kernel/process.c | 12 +++++++++++- > > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > > index 1540ab0fbf23..17b94007fed4 100644 > > > --- a/arch/arm64/kernel/process.c > > > +++ b/arch/arm64/kernel/process.c > > > @@ -625,6 +625,16 @@ unsigned long arch_align_stack(unsigned long sp) > > > return sp & ~0xf; > > > } > > > > > > +static void adjust_compat_task_affinity(struct task_struct *p) > > > +{ > > > + const struct cpumask *mask = system_32bit_el0_cpumask(); > > > + > > > + if (restrict_cpus_allowed_ptr(p, mask)) > > > + set_cpus_allowed_ptr(p, mask); > > > > This silently destroys user state, at the very least that ought to go > > with a WARN or something. Ideally SIGKILL though. What's to stop someone > > from doing a sched_setaffinity() right after the execve, same problem. > > So why bother.. > > It's no different to CPU hot-unplug though, is it? From the perspective of > the 32-bit task, the 64-bit-only cores were hot-unplugged at the point of > execve(). Calls to sched_setaffinity() for 32-bit tasks will reject attempts > to include 64-bit-only cores. select_fallback_rq() has a printk() in to at least notify things went bad. But I don't particularly like the current hotplug semantics; I've wanted to disallow the hotplug when it would result in this case, but computing that is tricky. It's one of those things that's forever on the todo list ... :/ > I initially wanted to punt this all to userspace, but one of the big > problems with that is when a 64-bit task is running on a CPU only capable > of running 64-bit tasks and it execve()s a 32-bit task. At the point, we > have to do something because we can't even run the new task for it to do > a sched_affinity() call (and we also can't deliver SIGILL). Userspace can see that one coming though... I suppose you can simply make the execve fail before the point of no return.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org> To: Will Deacon <will@kernel.org> Cc: linux-arch@vger.kernel.org, Marc Zyngier <maz@kernel.org>, kernel-team@android.com, Vincent Guittot <vincent.guittot@linaro.org>, Juri Lelli <juri.lelli@redhat.com>, Quentin Perret <qperret@google.com>, Catalin Marinas <catalin.marinas@arm.com>, Johannes Weiner <hannes@cmpxchg.org>, linux-kernel@vger.kernel.org, Qais Yousef <qais.yousef@arm.com>, Ingo Molnar <mingo@redhat.com>, Li Zefan <lizefan@huawei.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Tejun Heo <tj@kernel.org>, Suren Baghdasaryan <surenb@google.com>, Morten Rasmussen <morten.rasmussen@arm.com>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Date: Thu, 19 Nov 2020 17:42:03 +0100 [thread overview] Message-ID: <20201119164203.GU3121392@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20201119162822.GA4582@willie-the-truck> On Thu, Nov 19, 2020 at 04:28:23PM +0000, Will Deacon wrote: > On Thu, Nov 19, 2020 at 05:14:48PM +0100, Peter Zijlstra wrote: > > On Fri, Nov 13, 2020 at 09:37:13AM +0000, Will Deacon wrote: > > > When exec'ing a 32-bit task on a system with mismatched support for > > > 32-bit EL0, try to ensure that it starts life on a CPU that can actually > > > run it. > > > > > > Signed-off-by: Will Deacon <will@kernel.org> > > > --- > > > arch/arm64/kernel/process.c | 12 +++++++++++- > > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > > index 1540ab0fbf23..17b94007fed4 100644 > > > --- a/arch/arm64/kernel/process.c > > > +++ b/arch/arm64/kernel/process.c > > > @@ -625,6 +625,16 @@ unsigned long arch_align_stack(unsigned long sp) > > > return sp & ~0xf; > > > } > > > > > > +static void adjust_compat_task_affinity(struct task_struct *p) > > > +{ > > > + const struct cpumask *mask = system_32bit_el0_cpumask(); > > > + > > > + if (restrict_cpus_allowed_ptr(p, mask)) > > > + set_cpus_allowed_ptr(p, mask); > > > > This silently destroys user state, at the very least that ought to go > > with a WARN or something. Ideally SIGKILL though. What's to stop someone > > from doing a sched_setaffinity() right after the execve, same problem. > > So why bother.. > > It's no different to CPU hot-unplug though, is it? From the perspective of > the 32-bit task, the 64-bit-only cores were hot-unplugged at the point of > execve(). Calls to sched_setaffinity() for 32-bit tasks will reject attempts > to include 64-bit-only cores. select_fallback_rq() has a printk() in to at least notify things went bad. But I don't particularly like the current hotplug semantics; I've wanted to disallow the hotplug when it would result in this case, but computing that is tricky. It's one of those things that's forever on the todo list ... :/ > I initially wanted to punt this all to userspace, but one of the big > problems with that is when a 64-bit task is running on a CPU only capable > of running 64-bit tasks and it execve()s a 32-bit task. At the point, we > have to do something because we can't even run the new task for it to do > a sched_affinity() call (and we also can't deliver SIGILL). Userspace can see that one coming though... I suppose you can simply make the execve fail before the point of no return. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-11-19 16:42 UTC|newest] Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-13 9:37 [PATCH v3 00/14] An alternative series for asymmetric AArch32 systems Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 01/14] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 02/14] arm64: Allow mismatched 32-bit EL0 support Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-19 11:27 ` Valentin Schneider 2020-11-19 11:27 ` Valentin Schneider 2020-11-19 13:12 ` Will Deacon 2020-11-19 13:12 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 04/14] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 05/14] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 06/14] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-19 9:18 ` Quentin Perret 2020-11-19 9:18 ` Quentin Perret 2020-11-19 11:03 ` Quentin Perret 2020-11-19 11:03 ` Quentin Perret 2020-11-19 11:05 ` Will Deacon 2020-11-19 11:05 ` Will Deacon 2020-11-19 11:27 ` Valentin Schneider 2020-11-19 11:27 ` Valentin Schneider 2020-11-19 13:13 ` Will Deacon 2020-11-19 13:13 ` Will Deacon 2020-11-19 14:54 ` Valentin Schneider 2020-11-19 14:54 ` Valentin Schneider 2020-11-19 16:41 ` Will Deacon 2020-11-19 16:41 ` Will Deacon 2020-11-19 12:47 ` Valentin Schneider 2020-11-19 12:47 ` Valentin Schneider 2020-11-19 13:13 ` Will Deacon 2020-11-19 13:13 ` Will Deacon 2020-11-19 14:54 ` Valentin Schneider 2020-11-19 14:54 ` Valentin Schneider 2020-11-19 16:09 ` Peter Zijlstra 2020-11-19 16:09 ` Peter Zijlstra 2020-11-19 16:57 ` Valentin Schneider 2020-11-19 16:57 ` Valentin Schneider 2020-11-19 19:25 ` Will Deacon 2020-11-19 19:25 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-19 9:24 ` Quentin Perret 2020-11-19 9:24 ` Quentin Perret 2020-11-19 11:06 ` Will Deacon 2020-11-19 11:06 ` Will Deacon 2020-11-19 16:19 ` Peter Zijlstra 2020-11-19 16:19 ` Peter Zijlstra 2020-11-19 16:30 ` Will Deacon 2020-11-19 16:30 ` Will Deacon 2020-11-19 16:44 ` Peter Zijlstra 2020-11-19 16:44 ` Peter Zijlstra 2020-11-19 16:51 ` Will Deacon 2020-11-19 16:51 ` Will Deacon 2020-11-19 16:14 ` Peter Zijlstra 2020-11-19 16:14 ` Peter Zijlstra 2020-11-19 16:28 ` Will Deacon 2020-11-19 16:28 ` Will Deacon 2020-11-19 16:42 ` Peter Zijlstra [this message] 2020-11-19 16:42 ` Peter Zijlstra 2020-11-19 16:48 ` Will Deacon 2020-11-19 16:48 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 09/14] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-19 9:29 ` Quentin Perret 2020-11-19 9:29 ` Quentin Perret 2020-11-19 11:06 ` Will Deacon 2020-11-19 11:06 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 10/14] sched: Introduce arch_cpu_allowed_mask() to limit fallback rq selection Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-19 9:38 ` Quentin Perret 2020-11-19 9:38 ` Quentin Perret 2020-11-19 11:07 ` Will Deacon 2020-11-19 11:07 ` Will Deacon 2020-11-19 20:39 ` Will Deacon 2020-11-19 20:39 ` Will Deacon 2020-11-23 14:48 ` Quentin Perret 2020-11-23 14:48 ` Quentin Perret 2020-11-13 9:37 ` [PATCH v3 11/14] sched: Reject CPU affinity changes based on arch_cpu_allowed_mask() Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-19 9:47 ` Quentin Perret 2020-11-19 9:47 ` Quentin Perret 2020-11-19 11:07 ` Will Deacon 2020-11-19 11:07 ` Will Deacon 2020-11-19 14:30 ` Quentin Perret 2020-11-19 14:30 ` Quentin Perret 2020-11-19 16:44 ` Will Deacon 2020-11-19 16:44 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 12/14] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 13/14] arm64: Implement arch_cpu_allowed_mask() Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-13 9:37 ` [PATCH v3 14/14] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon 2020-11-13 9:37 ` Will Deacon 2020-11-19 16:11 ` [PATCH v3 00/14] An alternative series for asymmetric AArch32 systems Peter Zijlstra 2020-11-19 16:11 ` Peter Zijlstra 2020-11-19 16:39 ` Will Deacon 2020-11-19 16:39 ` Will Deacon
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