From: Qais Yousef <qais.yousef@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>,
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 13:09:41 +0000 [thread overview]
Message-ID: <20201127130941.pr3grbcir6jdtzwa@e107158-lin.cambridge.arm.com> (raw)
In-Reply-To: <20201124155039.13804-3-will@kernel.org>
On 11/24/20 15:50, Will Deacon wrote:
> When confronted with a mixture of CPUs, some of which support 32-bit
Confronted made me laugh, well chosen word! :D
For some reason made me think of this :p
https://www.youtube.com/watch?v=NJbXPzSPzxc&t=1m33s
> 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
nit: would UNUSED be better here? Worth adding a comment as to why too?
> #define ARM64_HARDEN_EL2_VECTORS 14
> #define ARM64_HAS_CNP 15
> #define ARM64_HAS_NO_FPSIMD 16
[...]
> +static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int scope)
> +{
> + if (!has_cpuid_feature(entry, scope))
> + return allow_mismatched_32bit_el0;
If a user passes the command line by mistake on a 64bit only system, this will
return true. I'll be honest, I'm not entirely sure what the impact is. I get
lost in the features maze. It is nicely encapsulated, but hard to navigate for
the none initiated :-)
Thanks
--
Qais Yousef
> +
> + if (scope == SCOPE_SYSTEM)
> + pr_info("detected: 32-bit EL0 Support\n");
> +
> + return true;
> +}
> +
> static bool has_useable_gicv3_cpuif(const struct arm64_cpu_capabilities *entry, int scope)
> {
> bool has_sre;
> @@ -1803,10 +1890,9 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> },
> #endif /* CONFIG_ARM64_VHE */
> {
> - .desc = "32-bit EL0 Support",
> - .capability = ARM64_HAS_32BIT_EL0,
> + .capability = ARM64_HAS_32BIT_EL0_DO_NOT_USE,
> .type = ARM64_CPUCAP_SYSTEM_FEATURE,
> - .matches = has_cpuid_feature,
> + .matches = has_32bit_el0,
> .sys_reg = SYS_ID_AA64PFR0_EL1,
> .sign = FTR_UNSIGNED,
> .field_pos = ID_AA64PFR0_EL0_SHIFT,
> @@ -2299,7 +2385,7 @@ static const struct arm64_cpu_capabilities compat_elf_hwcaps[] = {
> {},
> };
next prev parent reply other threads:[~2020-11-27 13:10 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
2020-11-27 13:09 ` Qais Yousef [this message]
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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