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

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Date: Fri, 21 Jun 2024 18:03:30 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Audra Mitchell <audra@...hat.com>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
 aarcange@...hat.com, rppt@...ux.vnet.ibm.com, shli@...com,
 peterx@...hat.com, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, shuah@...nel.org,
 linux-kselftest@...r.kernel.org, raquini@...hat.com
Subject: Re: [PATCH v2 1/3] Fix userfaultfd_api to return EINVAL as expected

On Fri, 21 Jun 2024 14:12:22 -0400 Audra Mitchell <audra@...hat.com> 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.