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ANDROID: arm64: Disallow offlining the last aarch32 cpu

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On asym aarch32 systems, bringing the last aarch32 cpu would cause any
running 32bit application to crash. To protect against that, we ensure
that we block the offlining operation of the last online cpu in
aarch32_el0_mask.

Suspend/hibernation and kexec operation should continue to work as
intended.

This is a different approach compared to the original one [1]. We should
be able to convert this to a vendor hook if there's a desire to do so.

[1] http://linux-arm.org/git?p=linux-power.git;a=commit;h=e6b567c1cc07dd1690e5d34b6a93ab9819ab2eeb

Bug: 168847043
Reason: Needed for bringup. Revert when upstream patch is available
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Change-Id: Ie8a2372d7b7db3c3580f19d724be183f988a5895
This commit is contained in:
Qais Yousef
2020-09-15 12:47:10 +01:00
committed by Todd Kjos
parent cacae105ed
commit d4313b326c
2 changed files with 57 additions and 3 deletions
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6
arch/arm64/Kconfig
View File

@@ -1896,8 +1896,10 @@ config ASYMMETRIC_AARCH32
CPU configurations. Once the AArch32 EL0 support is detected
on a CPU, the feature is made available to user space to allow
the execution of 32-bit (compat) applications by migrating
them to the capable CPUs. Offlining such CPUs leads to 32-bit
applications being killed.
them to the capable CPUs. You will not be able to offline all
such CPUs to prevent any running 32-bit application from being
killed. I.e: we guarantee there will always be at least one
32-bit capable CPU online.
If unsure say N.

54
arch/arm64/kernel/smp.c
View File

@@ -95,6 +95,54 @@ static inline int op_cpu_kill(unsigned int cpu)
}
#endif
#ifdef CONFIG_ASYMMETRIC_AARCH32
static int last_aarch32_cpu = -1;
static cpumask_t aarch32_online;
static void asym_aarch32_online(void)
{
/*
* Since we onlined another cpu, restore the hotpluggability of
* the last AAarch32 cpu if it was disabled.
*/
cpumask_and(&aarch32_online, &aarch32_el0_mask, cpu_online_mask);
if (last_aarch32_cpu >= 0 &&
cpumask_weight(&aarch32_online) > 1) {
struct device *dev;
dev = get_cpu_device(last_aarch32_cpu);
dev->offline_disabled = 0;
last_aarch32_cpu = -1;
}
}
static void asym_aarch32_offline(void)
{
/* Don't let the last AArch32-compatible CPU go down */
if (!cpumask_empty(&aarch32_el0_mask)) {
cpumask_and(&aarch32_online, &aarch32_el0_mask, cpu_online_mask);
/*
* If we're left with only one AAarch32 cpu, prevent it from
* being offlined.
*/
if (cpumask_weight(&aarch32_online) == 1) {
struct device *dev;
last_aarch32_cpu = cpumask_first(&aarch32_online);
dev = get_cpu_device(last_aarch32_cpu);
dev->offline_disabled = 1;
}
}
}
#else
static void asym_aarch32_online(void) {}
static void asym_aarch32_offline(void) {}
#endif
/*
* Boot a secondary CPU, and assign it the specified idle task.
@@ -139,8 +187,10 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
*/
wait_for_completion_timeout(&cpu_running,
msecs_to_jiffies(5000));
if (cpu_online(cpu))
if (cpu_online(cpu)) {
asym_aarch32_online();
return 0;
}
pr_crit("CPU%u: failed to come online\n", cpu);
secondary_data.task = NULL;
@@ -317,6 +367,8 @@ int __cpu_disable(void)
set_cpu_online(cpu, false);
ipi_teardown(cpu);
asym_aarch32_offline();
/*
* OK - migrate IRQs away from this CPU
*/