On 11/24/20 15:50, 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 <w...@kernel.org>
> ---
> arch/arm64/kernel/process.c | 42 ++++++++++++++++++++++++++++++++++++-
> 1 file changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 1540ab0fbf23..72116b0c7c73 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -31,6 +31,7 @@
> #include <linux/interrupt.h>
> #include <linux/init.h>
> #include <linux/cpu.h>
> +#include <linux/cpuset.h>
> #include <linux/elfcore.h>
> #include <linux/pm.h>
> #include <linux/tick.h>
> @@ -625,6 +626,45 @@ unsigned long arch_align_stack(unsigned long sp)
> return sp & ~0xf;
> }
>
> +static void adjust_compat_task_affinity(struct task_struct *p)
> +{
> + cpumask_var_t cpuset_mask;
> + const struct cpumask *possible_mask = system_32bit_el0_cpumask();
> + const struct cpumask *newmask = possible_mask;
> +
> + /*
> + * Restrict the CPU affinity mask for a 32-bit task so that it contains
> + * only the 32-bit-capable subset of its original CPU mask. If this is
> + * empty, then try again with the cpuset allowed mask. If that fails,
> + * forcefully override it with the set of all 32-bit-capable CPUs that
> + * we know about.
> + *
> + * From the perspective of the task, this looks similar to what would
> + * happen if the 64-bit-only CPUs were hot-unplugged at the point of
> + * execve().
> + */
> + if (!restrict_cpus_allowed_ptr(p, possible_mask))
> + goto out;
> +
> + if (alloc_cpumask_var(&cpuset_mask, GFP_KERNEL)) {
> + cpuset_cpus_allowed(p, cpuset_mask);
> + if (cpumask_and(cpuset_mask, cpuset_mask, possible_mask)) {
> + newmask = cpuset_mask;
> + goto out_set_mask;
> + }
> + }
Wouldn't it be better to move this logic to restrict_cpus_allowed_ptr()?
I think it should always take cpusets into account and it's not special to
this particular handling here, no?
> +
> + if (printk_ratelimit()) {
> + printk_deferred("Overriding affinity for 32-bit process %d (%s)
> to CPUs %*pbl\n",
> + task_pid_nr(p), p->comm,
> cpumask_pr_args(newmask));
> + }
We have 2 cases where the affinity could have been overridden but we won't
print anything:
1. restrict_cpus_allowed_ptr()
2. intersection of cpuset_mask and possible mask drops some cpus.
Shouldn't we print something in these cases too?
IMO it would be better to move this print to restrict_cpus_allowed_ptr() too.
Thanks
--
Qais Yousef
> +out_set_mask:
> + set_cpus_allowed_ptr(p, newmask);
> + free_cpumask_var(cpuset_mask);
> +out:
> + set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
> +}
> +
> /*
> * Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
> */
> @@ -635,7 +675,7 @@ void arch_setup_new_exec(void)
> if (is_compat_task()) {
> mmflags = MMCF_AARCH32;
> if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
> - set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
> + adjust_compat_task_affinity(current);
> }
>
> current->mm->context.flags = mmflags;
> --
> 2.29.2.454.gaff20da3a2-goog
>
