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 <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; > + } > + } 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 >