From: Will Deacon <will@kernel.org>
To: Marc Zyngier <maz@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>,
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>,
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 v4 02/14] arm64: Allow mismatched 32-bit EL0 support
Date: Fri, 27 Nov 2020 11:50:24 +0000 [thread overview]
Message-ID: <20201127115024.GA20564@willie-the-truck> (raw)
In-Reply-To: <d7dfc12ca87d65fad79bfe2cd697a28d@kernel.org>
On Fri, Nov 27, 2020 at 10:25:06AM +0000, Marc Zyngier wrote:
> On 2020-11-24 15:50, Will Deacon wrote:
> > When confronted with a mixture of CPUs, some of which support 32-bit
> > applications and others which don't, we quite sensibly treat the system
> > as 64-bit only for userspace and prevent execve() of 32-bit binaries.
> >
> > Unfortunately, some crazy folks have decided to build systems like this
> > with the intention of running 32-bit applications, so relax our
> > sanitisation logic to continue to advertise 32-bit support to userspace
> > on these systems and track the real 32-bit capable cores in a cpumask
> > instead. For now, the default behaviour remains but will be tied to
> > a command-line option in a later patch.
> >
> > Signed-off-by: Will Deacon <will@kernel.org>
> > ---
> > arch/arm64/include/asm/cpucaps.h | 2 +-
> > arch/arm64/include/asm/cpufeature.h | 8 ++-
> > arch/arm64/kernel/cpufeature.c | 106 ++++++++++++++++++++++++++--
> > 3 files changed, 107 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/cpucaps.h
> > b/arch/arm64/include/asm/cpucaps.h
> > index e7d98997c09c..e6f0eb4643a0 100644
> > --- a/arch/arm64/include/asm/cpucaps.h
> > +++ b/arch/arm64/include/asm/cpucaps.h
> > @@ -20,7 +20,7 @@
> > #define ARM64_ALT_PAN_NOT_UAO 10
> > #define ARM64_HAS_VIRT_HOST_EXTN 11
> > #define ARM64_WORKAROUND_CAVIUM_27456 12
> > -#define ARM64_HAS_32BIT_EL0 13
> > +#define ARM64_HAS_32BIT_EL0_DO_NOT_USE 13
> > #define ARM64_HARDEN_EL2_VECTORS 14
> > #define ARM64_HAS_CNP 15
> > #define ARM64_HAS_NO_FPSIMD 16
> > diff --git a/arch/arm64/include/asm/cpufeature.h
> > b/arch/arm64/include/asm/cpufeature.h
> > index 97244d4feca9..f447d313a9c5 100644
> > --- a/arch/arm64/include/asm/cpufeature.h
> > +++ b/arch/arm64/include/asm/cpufeature.h
> > @@ -604,9 +604,15 @@ static inline bool
> > cpu_supports_mixed_endian_el0(void)
> > return id_aa64mmfr0_mixed_endian_el0(read_cpuid(ID_AA64MMFR0_EL1));
> > }
> >
> > +const struct cpumask *system_32bit_el0_cpumask(void);
> > +DECLARE_STATIC_KEY_FALSE(arm64_mismatched_32bit_el0);
> > +
> > static inline bool system_supports_32bit_el0(void)
> > {
> > - return cpus_have_const_cap(ARM64_HAS_32BIT_EL0);
> > + u64 pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
> > +
> > + return id_aa64pfr0_32bit_el0(pfr0) ||
> > + static_branch_unlikely(&arm64_mismatched_32bit_el0);
>
> nit: swapping the two sides of this expression has the potential
> for slightly better code, resulting in better performance on
> these asymmetric systems. Not a big real, but since this lands
> on the fast path on vcpu exit, I'll take every bit of optimisation.
I'll swap 'em, thanks.
Will
next prev parent reply other threads:[~2020-11-27 11:50 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-24 15:50 [PATCH v4 00/14] An alternative series for asymmetric AArch32 systems Will Deacon
2020-11-24 15:50 ` [PATCH v4 01/14] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2020-11-24 15:50 ` [PATCH v4 02/14] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2020-11-27 10:25 ` Marc Zyngier
2020-11-27 11:50 ` Will Deacon [this message]
2020-11-27 13:09 ` Qais Yousef
2020-12-01 16:56 ` Will Deacon
2020-12-02 13:16 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2020-11-27 10:26 ` Marc Zyngier
2020-11-27 11:53 ` Will Deacon
2020-11-27 17:14 ` Marc Zyngier
2020-11-27 17:24 ` Quentin Perret
2020-11-27 18:16 ` Marc Zyngier
2020-12-01 16:57 ` Will Deacon
2020-12-02 8:18 ` Marc Zyngier
2020-12-02 17:27 ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 04/14] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2020-11-27 13:12 ` Qais Yousef
2020-12-01 16:56 ` Will Deacon
2020-12-02 13:52 ` Qais Yousef
2020-12-02 17:42 ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 05/14] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2020-11-24 15:50 ` [PATCH v4 06/14] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
2020-11-27 13:17 ` Qais Yousef
2020-12-01 16:56 ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity Will Deacon
2020-11-27 9:49 ` Quentin Perret
2020-11-27 13:19 ` Qais Yousef
2020-12-01 16:56 ` Will Deacon
2020-12-02 13:06 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon
2020-11-27 10:01 ` Quentin Perret
2020-11-27 13:23 ` Qais Yousef
2020-12-01 16:55 ` Will Deacon
2020-12-02 14:07 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 09/14] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon
2020-11-27 13:32 ` Qais Yousef
2020-11-30 17:05 ` Qais Yousef
2020-11-30 17:36 ` Quentin Perret
2020-12-01 11:58 ` Qais Yousef
2020-12-01 12:37 ` Quentin Perret
2020-12-01 14:11 ` Qais Yousef
2020-12-01 15:56 ` Quentin Perret
2020-12-01 22:30 ` Will Deacon
2020-12-02 11:34 ` Qais Yousef
2020-12-02 11:33 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 10/14] sched: Introduce arch_task_cpu_possible_mask() to limit fallback rq selection Will Deacon
2020-11-24 15:50 ` [PATCH v4 11/14] sched: Reject CPU affinity changes based on arch_task_cpu_possible_mask() Will Deacon
2020-11-27 9:54 ` Quentin Perret
2020-11-24 15:50 ` [PATCH v4 12/14] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon
2020-11-27 13:41 ` Qais Yousef
2020-12-01 22:13 ` Will Deacon
2020-12-02 12:59 ` Qais Yousef
2020-12-02 17:42 ` Will Deacon
2020-12-02 18:08 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 13/14] arm64: Implement arch_task_cpu_possible_mask() Will Deacon
2020-11-27 13:41 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 14/14] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon
2020-11-27 13:58 ` [PATCH v4 00/14] An alternative series for asymmetric AArch32 systems Qais Yousef
2020-12-05 20:43 ` Pavel Machek
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