On Tuesday 24 Nov 2020 at 15:50:33 (+0000), 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 <will@xxxxxxxxxx>
> ---
> 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;
> + }
> + }
> +
> + 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));
> + }
> +out_set_mask:
> + set_cpus_allowed_ptr(p, newmask);
> + free_cpumask_var(cpuset_mask);
> +out:
> + set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
> +}
This starts to look an awful lot like select_fallback_rq(), but I
suppose we shouldn't bother factoring out that code yet as we probably
don't want this pattern to be re-used all over, so:
Reviewed-by: Quentin Perret <qperret@xxxxxxxxxx>
Thanks,
Quentin
