[PATCH v2] docs: make kptr_restrict and hash_pointers reference each other

[PATCH v2] docs: make kptr_restrict and hash_pointers reference each other

[Marc Herbert]

vsprintf.c uses a mix of the `kernel.kptr_restrict` sysctl and the
`hash_pointers` boot param to control pointer hashing. But that wasn't
possible to tell without looking at the source code.

They have a different focus and purpose. To avoid wasting the time of
users trying to use one instead of the other, simply have them reference
each other in the Documentation.

Signed-off-by: Marc Herbert <marc.herbert@linux.intel.com>
---
Please just go ahead with any minor correction(s); I mean do not ask
for my opinion.

Changes in v2:
- Rebased on today's docs-next/master to fix textual, unrelated conflict
- Stop using backquotes in kernel-parameters.txt for consistency
- Link to v1: https://patch.msgid.link/20251205-doc-hash-ptr-v1-1-573966cfa404@linux.intel.com
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 Documentation/admin-guide/sysctl/kernel.rst     | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a8d0afde7f85..b189dfd60059 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1969,6 +1969,9 @@ Kernel parameters
 				 param "no_hash_pointers" is an alias for
 				 this mode.
 
+			For controlling hashing dynamically at runtime,
+			use the "kernel.kptr_restrict" sysctl instead.
+
 	hashdist=	[KNL,NUMA] Large hashes allocated during boot
 			are distributed across NUMA nodes.  Defaults on
 			for 64-bit NUMA, off otherwise.
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 239da22c4e28..0315eb7ee6d4 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -591,6 +591,9 @@ if leaking kernel pointer values to unprivileged users is a concern.
 When ``kptr_restrict`` is set to 2, kernel pointers printed using
 %pK will be replaced with 0s regardless of privileges.
 
+For disabling these security restrictions early at boot time (and once
+for all), use the ``hash_pointers`` boot parameter instead.
+
 softlockup_sys_info & hardlockup_sys_info
 =========================================
 A comma separated list of extra system information to be dumped when

---
base-commit: f0b9d8eb98dfee8d00419aa07543bdc2c1a44fb1
change-id: 20251204-doc-hash-ptr-00e46e1a5398

Best regards,
--  
Marc Herbert <marc.herbert@linux.intel.com>

Re: [PATCH v2] docs: make kptr_restrict and hash_pointers reference each other

[Randy Dunlap]

On 1/7/26 12:21 PM, Marc Herbert wrote:
> vsprintf.c uses a mix of the `kernel.kptr_restrict` sysctl and the
> `hash_pointers` boot param to control pointer hashing. But that wasn't
> possible to tell without looking at the source code.
> 
> They have a different focus and purpose. To avoid wasting the time of
> users trying to use one instead of the other, simply have them reference
> each other in the Documentation.
> 
> Signed-off-by: Marc Herbert <marc.herbert@linux.intel.com>
> ---
> Please just go ahead with any minor correction(s); I mean do not ask
> for my opinion.
> 
> Changes in v2:
> - Rebased on today's docs-next/master to fix textual, unrelated conflict
> - Stop using backquotes in kernel-parameters.txt for consistency
> - Link to v1: https://patch.msgid.link/20251205-doc-hash-ptr-v1-1-573966cfa404@linux.intel.com
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 3 +++
>  Documentation/admin-guide/sysctl/kernel.rst     | 3 +++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index a8d0afde7f85..b189dfd60059 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1969,6 +1969,9 @@ Kernel parameters
>  				 param "no_hash_pointers" is an alias for
>  				 this mode.
>  
> +			For controlling hashing dynamically at runtime,
> +			use the "kernel.kptr_restrict" sysctl instead.

			See Documentation/admin-guide/sysctl/kernel.rst.
> +
>  	hashdist=	[KNL,NUMA] Large hashes allocated during boot
>  			are distributed across NUMA nodes.  Defaults on
>  			for 64-bit NUMA, off otherwise.
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index 239da22c4e28..0315eb7ee6d4 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -591,6 +591,9 @@ if leaking kernel pointer values to unprivileged users is a concern.
>  When ``kptr_restrict`` is set to 2, kernel pointers printed using
>  %pK will be replaced with 0s regardless of privileges.
>  
> +For disabling these security restrictions early at boot time (and once
> +for all), use the ``hash_pointers`` boot parameter instead.

   (once and for all),
or
   (until the next boot),

> +
>  softlockup_sys_info & hardlockup_sys_info
>  =========================================
>  A comma separated list of extra system information to be dumped when
> 
> ---
> base-commit: f0b9d8eb98dfee8d00419aa07543bdc2c1a44fb1
> change-id: 20251204-doc-hash-ptr-00e46e1a5398
> 
> Best regards,
> --  
> Marc Herbert <marc.herbert@linux.intel.com>
> 
> 


Acked-by: Randy Dunlap <rdunlap@infradead.org>

Thanks.
-- 
~Randy

Re: [PATCH v2] docs: make kptr_restrict and hash_pointers reference each other

[Jonathan Corbet]

Marc Herbert <marc.herbert@linux.intel.com> writes:

> vsprintf.c uses a mix of the `kernel.kptr_restrict` sysctl and the
> `hash_pointers` boot param to control pointer hashing. But that wasn't
> possible to tell without looking at the source code.
>
> They have a different focus and purpose. To avoid wasting the time of
> users trying to use one instead of the other, simply have them reference
> each other in the Documentation.
>
> Signed-off-by: Marc Herbert <marc.herbert@linux.intel.com>
> ---
> Please just go ahead with any minor correction(s); I mean do not ask
> for my opinion.
>
> Changes in v2:
> - Rebased on today's docs-next/master to fix textual, unrelated conflict
> - Stop using backquotes in kernel-parameters.txt for consistency
> - Link to v1: https://patch.msgid.link/20251205-doc-hash-ptr-v1-1-573966cfa404@linux.intel.com
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 3 +++
>  Documentation/admin-guide/sysctl/kernel.rst     | 3 +++
>  2 files changed, 6 insertions(+)

Applied, thanks.

jon