On 01/31, Alex Thorlton wrote:
>
> This patch adds a VM_INIT_DEF_MASK,
Perhaps it makes sense to tell a bit more... We add this mask to preserve
VM_NOHUGEPAGE after fork/exec. And this is obviously affects s390, say the
result of KVM_S390_ENABLE_SIE will be preserved.
I hope this is fine, but should be documented and it would be nice to have
the acks from Gerald.
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1996,6 +1996,23 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long,
> arg2, unsigned long, arg3,
> if (arg2 || arg3 || arg4 || arg5)
> return -EINVAL;
> return current->no_new_privs ? 1 : 0;
> + case PR_GET_THP_DISABLE:
> + if (arg2 || arg3 || arg4 || arg5)
> + return -EINVAL;
Cosmetic, but PR_GET_THP_DISABLE only needs to check arg2.
OTOH,
> + case PR_SET_THP_DISABLE:
> + if (arg3 || arg4 || arg5)
> + return -EINVAL;
> + down_write(&me->mm->mmap_sem);
> + if (option == PR_SET_THP_DISABLE) {
> + if (arg2)
> + me->mm->def_flags |= VM_NOHUGEPAGE;
> + else
> + me->mm->def_flags &= ~VM_NOHUGEPAGE;
> + } else {
> + error = !!(me->mm->def_flags & VM_NOHUGEPAGE);
> + }
> + up_write(&me->mm->mmap_sem);
> + break;
Perhaps _GET_ doesn't even need ->mmap_sem, I do not see how the lockless
"&" can get the inconsistent result. But I am fine either way.
Oleg.
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