Re: [PATCH v2 1/3] Fix userfaultfd_api to return EINVAL as expected

[Andrew Morton]

On Fri, 21 Jun 2024 14:12:22 -0400 Audra Mitchell <audra@xxxxxxxxxx> wrote:

> Currently if we request a feature that is not set in the Kernel
> config we fail silently and return all the available features. However,
> the man page indicates we should return an EINVAL.
> 
> We need to fix this issue since we can end up with a Kernel warning
> should a program request the feature UFFD_FEATURE_WP_UNPOPULATED on
> a kernel with the config not set with this feature.
> 
>  [  200.812896] WARNING: CPU: 91 PID: 13634 at mm/memory.c:1660 zap_pte_range+0x43d/0x660
>  [  200.820738] Modules linked in:
>  [  200.869387] CPU: 91 PID: 13634 Comm: userfaultfd Kdump: loaded Not tainted 6.9.0-rc5+ #8
>  [  200.877477] Hardware name: Dell Inc. PowerEdge R6525/0N7YGH, BIOS 2.7.3 03/30/2022
>  [  200.885052] RIP: 0010:zap_pte_range+0x43d/0x660
> 
> Fixes: e06f1e1dd499 ("userfaultfd: wp: enabled write protection in userfaultfd API")

A userspace-triggerable WARN is bad.  I added cc:stable to this.