From: Mark Rutland <mark.rutland@arm.com> 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>, Peter Zijlstra <peterz@infradead.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>, Johannes Weiner <hannes@cmpxchg.org>, Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>, Vincent Guittot <vincent.guittot@linaro.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Dietmar Eggemann <dietmar.eggemann@arm.com>, Daniel Bristot de Oliveira <bristot@redhat.com>, Valentin Schneider <valentin.schneider@arm.com>, kernel-team@android.com Subject: Re: [PATCH v8 02/19] arm64: Allow mismatched 32-bit EL0 support Date: Fri, 4 Jun 2021 13:04:27 +0100 [thread overview] Message-ID: <20210604120352.GA67240@C02TD0UTHF1T.local> (raw) In-Reply-To: <20210604110526.GF2318@willie-the-truck> On Fri, Jun 04, 2021 at 12:05:27PM +0100, Will Deacon wrote: > On Fri, Jun 04, 2021 at 10:38:08AM +0100, Mark Rutland wrote: > > On Thu, Jun 03, 2021 at 06:44:14PM +0100, Will Deacon wrote: > > > On Thu, Jun 03, 2021 at 01:37:15PM +0100, Mark Rutland wrote: > > > > On Wed, Jun 02, 2021 at 05:47:02PM +0100, Will Deacon wrote: > > > > > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > > > > That said. I reckon this could be much cleaner if we maintained separate > > > > caps: > > > > > > > > ARM64_ALL_CPUS_HAVE_32BIT_EL0 > > > > ARM64_SOME_CPUS_HAVE_32BIT_EL0 > > > > > > > > ... and allow arm64_mismatched_32bit_el0 to be set dependent on > > > > ARM64_SOME_CPUS_HAVE_32BIT_EL0. With that, this can be simplified to: > > > > > > > > static inline bool system_supports_32bit_el0(void) > > > > { > > > > return (cpus_have_const_cap(ARM64_ALL_CPUS_HAVE_32BIT_EL0)) || > > > > static_branch_unlikely(&arm64_mismatched_32bit_el0)) > > > > > > Something similar was discussed in November last year but this falls > > > apart with late onlining because its not generally possible to tell whether > > > you've seen all the CPUs or not. > > > > Ah; is that for when your boot CPU set is all AArch32-capable, but a > > late-onlined CPU is not? > > > > I assume that we require at least one of the set of boot CPUs to be > > AArch32 cpable, and don't settle the compat hwcaps after userspace has > > started. > > Heh, you assume wrong :) > > When we allow the mismatch, then we do actually defer initialisation of > the compat hwcaps until we see a 32-bit CPU. That's fine, as they won't > be visible to userspace until then anyway (PER_LINUX32 is unavailable). That sounds quite scary, to me, though I don't have a concrete problem to hand. :/ Do we really need to support initializing that so late? For all other caps we've settled things when the boot CPUs come up, and it's unfortunate to have to treat this differently. I'll go see if there's anything that's liable to break today. Thanks, Mark
WARNING: multiple messages have this Message-ID (diff)
From: Mark Rutland <mark.rutland@arm.com> 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>, Peter Zijlstra <peterz@infradead.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>, Johannes Weiner <hannes@cmpxchg.org>, Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>, Vincent Guittot <vincent.guittot@linaro.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Dietmar Eggemann <dietmar.eggemann@arm.com>, Daniel Bristot de Oliveira <bristot@redhat.com>, Valentin Schneider <valentin.schneider@arm.com>, kernel-team@android.com Subject: Re: [PATCH v8 02/19] arm64: Allow mismatched 32-bit EL0 support Date: Fri, 4 Jun 2021 13:04:27 +0100 [thread overview] Message-ID: <20210604120352.GA67240@C02TD0UTHF1T.local> (raw) In-Reply-To: <20210604110526.GF2318@willie-the-truck> On Fri, Jun 04, 2021 at 12:05:27PM +0100, Will Deacon wrote: > On Fri, Jun 04, 2021 at 10:38:08AM +0100, Mark Rutland wrote: > > On Thu, Jun 03, 2021 at 06:44:14PM +0100, Will Deacon wrote: > > > On Thu, Jun 03, 2021 at 01:37:15PM +0100, Mark Rutland wrote: > > > > On Wed, Jun 02, 2021 at 05:47:02PM +0100, Will Deacon wrote: > > > > > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > > > > That said. I reckon this could be much cleaner if we maintained separate > > > > caps: > > > > > > > > ARM64_ALL_CPUS_HAVE_32BIT_EL0 > > > > ARM64_SOME_CPUS_HAVE_32BIT_EL0 > > > > > > > > ... and allow arm64_mismatched_32bit_el0 to be set dependent on > > > > ARM64_SOME_CPUS_HAVE_32BIT_EL0. With that, this can be simplified to: > > > > > > > > static inline bool system_supports_32bit_el0(void) > > > > { > > > > return (cpus_have_const_cap(ARM64_ALL_CPUS_HAVE_32BIT_EL0)) || > > > > static_branch_unlikely(&arm64_mismatched_32bit_el0)) > > > > > > Something similar was discussed in November last year but this falls > > > apart with late onlining because its not generally possible to tell whether > > > you've seen all the CPUs or not. > > > > Ah; is that for when your boot CPU set is all AArch32-capable, but a > > late-onlined CPU is not? > > > > I assume that we require at least one of the set of boot CPUs to be > > AArch32 cpable, and don't settle the compat hwcaps after userspace has > > started. > > Heh, you assume wrong :) > > When we allow the mismatch, then we do actually defer initialisation of > the compat hwcaps until we see a 32-bit CPU. That's fine, as they won't > be visible to userspace until then anyway (PER_LINUX32 is unavailable). That sounds quite scary, to me, though I don't have a concrete problem to hand. :/ Do we really need to support initializing that so late? For all other caps we've settled things when the boot CPUs come up, and it's unfortunate to have to treat this differently. I'll go see if there's anything that's liable to break today. Thanks, Mark _______________________________________________ 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:[~2021-06-04 12:04 UTC|newest] Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-02 16:47 [PATCH v8 00/19] Add support for 32-bit tasks on asymmetric AArch32 systems Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 01/19] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-03 12:38 ` Mark Rutland 2021-06-03 12:38 ` Mark Rutland 2021-06-03 17:24 ` Will Deacon 2021-06-03 17:24 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 02/19] arm64: Allow mismatched 32-bit EL0 support Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-03 12:37 ` Mark Rutland 2021-06-03 12:37 ` Mark Rutland 2021-06-03 17:44 ` Will Deacon 2021-06-03 17:44 ` Will Deacon 2021-06-04 9:38 ` Mark Rutland 2021-06-04 9:38 ` Mark Rutland 2021-06-04 11:05 ` Will Deacon 2021-06-04 11:05 ` Will Deacon 2021-06-04 12:04 ` Mark Rutland [this message] 2021-06-04 12:04 ` Mark Rutland 2021-06-04 13:50 ` Will Deacon 2021-06-04 13:50 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 03/19] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 04/19] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 05/19] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-04 17:10 ` Valentin Schneider 2021-06-04 17:10 ` Valentin Schneider 2021-06-07 17:04 ` Will Deacon 2021-06-07 17:04 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 06/19] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-04 17:11 ` Valentin Schneider 2021-06-04 17:11 ` Valentin Schneider 2021-06-07 17:20 ` Will Deacon 2021-06-07 17:20 ` Will Deacon 2021-06-10 10:20 ` Valentin Schneider 2021-06-10 10:20 ` Valentin Schneider 2021-06-02 16:47 ` [PATCH v8 07/19] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus() Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-04 17:11 ` Valentin Schneider 2021-06-04 17:11 ` Valentin Schneider 2021-06-02 16:47 ` [PATCH v8 08/19] sched: Reject CPU affinity changes based on task_cpu_possible_mask() Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-04 17:11 ` Valentin Schneider 2021-06-04 17:11 ` Valentin Schneider 2021-06-07 22:43 ` Will Deacon 2021-06-07 22:43 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 09/19] sched: Introduce task_struct::user_cpus_ptr to track requested affinity Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-04 17:12 ` Valentin Schneider 2021-06-04 17:12 ` Valentin Schneider 2021-06-02 16:47 ` [PATCH v8 10/19] sched: Split the guts of sched_setaffinity() into a helper function Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-04 17:12 ` Valentin Schneider 2021-06-04 17:12 ` Valentin Schneider 2021-06-02 16:47 ` [PATCH v8 11/19] sched: Allow task CPU affinity to be restricted on asymmetric systems Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-04 17:12 ` Valentin Schneider 2021-06-04 17:12 ` Valentin Schneider 2021-06-07 22:52 ` Will Deacon 2021-06-07 22:52 ` Will Deacon 2021-06-10 10:20 ` Valentin Schneider 2021-06-10 10:20 ` Valentin Schneider 2021-06-02 16:47 ` [PATCH v8 12/19] sched: Introduce task_cpus_dl_admissible() to check proposed affinity Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-03 9:43 ` Daniel Bristot de Oliveira 2021-06-03 9:43 ` Daniel Bristot de Oliveira 2021-06-03 9:52 ` Will Deacon 2021-06-03 9:52 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 13/19] arm64: Implement task_cpu_possible_mask() Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 14/19] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-03 9:45 ` Daniel Bristot de Oliveira 2021-06-03 9:45 ` Daniel Bristot de Oliveira 2021-06-02 16:47 ` [PATCH v8 15/19] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-03 12:58 ` Mark Rutland 2021-06-03 12:58 ` Mark Rutland 2021-06-03 17:40 ` Will Deacon 2021-06-03 17:40 ` Will Deacon 2021-06-04 9:49 ` Mark Rutland 2021-06-04 9:49 ` Mark Rutland 2021-06-04 12:14 ` Qais Yousef 2021-06-04 12:14 ` Qais Yousef 2021-06-02 16:47 ` [PATCH v8 16/19] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 17/19] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 18/19] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon 2021-06-02 16:47 ` Will Deacon 2021-06-02 16:47 ` [PATCH v8 19/19] Documentation: arm64: describe asymmetric 32-bit support Will Deacon 2021-06-02 16:47 ` Will Deacon
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