[PATCH RESEND] NUMA x86: add constraints check for nid parameters

[PATCH RESEND] NUMA x86: add constraints check for nid parameters

[Petr Holasek]

This patch adds constraints checks into __node_distance() and
numa_set_distance() functions. If from or to parameters are
lower than zero, it results into oops now.

Signed-off-by: Petr Holasek <pholasek@redhat.com>
---
 arch/x86/mm/numa.c |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index fbeaaf4..9e0ff2b 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -430,8 +430,9 @@ static int __init numa_alloc_distance(void)
  * calls are ignored until the distance table is reset with
  * numa_reset_distance().
  *
- * If @from or @to is higher than the highest known node at the time of
- * table creation or @distance doesn't make sense, the call is ignored.
+ * If @from or @to is higher than the highest known node or lower than zero
+ * at the time of table creation or @distance doesn't make sense, the call
+ * is ignored.
  * This is to allow simplification of specific NUMA config implementations.
  */
 void __init numa_set_distance(int from, int to, int distance)
@@ -439,7 +440,8 @@ void __init numa_set_distance(int from, int to, int distance)
 	if (!numa_distance && numa_alloc_distance() < 0)
 		return;
 
-	if (from >= numa_distance_cnt || to >= numa_distance_cnt) {
+	if (from >= numa_distance_cnt || to >= numa_distance_cnt ||
+			from < 0 || to < 0) {
 		printk_once(KERN_DEBUG "NUMA: Debug: distance out of bound, from=%d to=%d distance=%d\n",
 			    from, to, distance);
 		return;
@@ -457,7 +459,8 @@ void __init numa_set_distance(int from, int to, int distance)
 
 int __node_distance(int from, int to)
 {
-	if (from >= numa_distance_cnt || to >= numa_distance_cnt)
+	if (from < 0 || to < 0 ||
+			from >= numa_distance_cnt || to >= numa_distance_cnt)
 		return from == to ? LOCAL_DISTANCE : REMOTE_DISTANCE;
 	return numa_distance[from * numa_distance_cnt + to];
 }
-- 
1.7.6.4

Re: [PATCH RESEND] NUMA x86: add constraints check for nid parameters

[Andrew Morton]

On Thu,  1 Dec 2011 12:45:07 +0100
Petr Holasek <pholasek@redhat.com> wrote:

> This patch adds constraints checks into __node_distance() and
> numa_set_distance() functions. If from or to parameters are
> lower than zero, it results into oops now.

Passing negative numbers into __node_distance() sounds like a bug in
the caller, and this patch will remove our means of detecting that bug.

Perhaps we need to be told more about this patch.  Is the bug
user-triggerable?  If so, how?  How was this fault triggered? 
Etcetera.

Re: NUMA x86: add constraints check for nid parameters

[Petr Holasek]

On Thu, 01 Dec 2011, Andrew Morton wrote:

> Date: Thu, 1 Dec 2011 13:34:51 -0800
> From: Andrew Morton <akpm@linux-foundation.org>
> To: Petr Holasek <pholasek@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
>  "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org, Anton
>  Arapov <anton@redhat.com>
> Subject: Re: [PATCH RESEND] NUMA x86: add constraints check for nid
>  parameters
> 
> On Thu,  1 Dec 2011 12:45:07 +0100
> Petr Holasek <pholasek@redhat.com> wrote:
> 
> > This patch adds constraints checks into __node_distance() and
> > numa_set_distance() functions. If from or to parameters are
> > lower than zero, it results into oops now.
> 
> Passing negative numbers into __node_distance() sounds like a bug in
> the caller, and this patch will remove our means of detecting that bug.

That's true, but upper boundary is checked now, so why not to check lower?
Seems inconsistent to me - from this point of view even don't check anything
would be better for detecting bug in the caller.

> 
> Perhaps we need to be told more about this patch.  Is the bug
> user-triggerable?  If so, how?  How was this fault triggered? 
> Etcetera.
> 

AFAIK, neither __node_distance() nor numa_set_distance() aren't in any
path from user-space inputs. Their paramaters are based on ACPI tables
provided by HW vendors.

Re: NUMA x86: add constraints check for nid parameters

[Andrew Morton]

On Fri, 2 Dec 2011 00:14:42 +0100
Petr Holasek <pholasek@redhat.com> wrote:

> On Thu, 01 Dec 2011, Andrew Morton wrote:
> 
> > Date: Thu, 1 Dec 2011 13:34:51 -0800
> > From: Andrew Morton <akpm@linux-foundation.org>
> > To: Petr Holasek <pholasek@redhat.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
> >  "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org, Anton
> >  Arapov <anton@redhat.com>
> > Subject: Re: [PATCH RESEND] NUMA x86: add constraints check for nid
> >  parameters
> > 
> > On Thu,  1 Dec 2011 12:45:07 +0100
> > Petr Holasek <pholasek@redhat.com> wrote:
> > 
> > > This patch adds constraints checks into __node_distance() and
> > > numa_set_distance() functions. If from or to parameters are
> > > lower than zero, it results into oops now.
> > 
> > Passing negative numbers into __node_distance() sounds like a bug in
> > the caller, and this patch will remove our means of detecting that bug.
> 
> That's true, but upper boundary is checked now, so why not to check lower?

Because it adds more code to the kernel and can hide bugs?

> Seems inconsistent to me - from this point of view even don't check anything
> would be better for detecting bug in the caller.
> 
> > 
> > Perhaps we need to be told more about this patch.  Is the bug
> > user-triggerable?  If so, how?  How was this fault triggered? 
> > Etcetera.
> > 
> 
> AFAIK, neither __node_distance() nor numa_set_distance() aren't in any
> path from user-space inputs. Their paramaters are based on ACPI tables
> provided by HW vendors.

That didn't answer my questions.  Have you observed any problems in
this code?  If so, please fully describe them.  Or was it purely from
code inspection?

If what we're doing here is to be defensive against buggy BIOS tables
(a good idea) then we should validate the BIOS table values as close as
possible to the point where they were read frmo the BIOS.  And we should
(probably) emit a warning if a bad table entry is detected, rather than
silently fixing it up.

Re: NUMA x86: add constraints check for nid parameters

[Petr Holasek]

On Thu, 01 Dec 2011, Andrew Morton wrote:
> 
> On Fri, 2 Dec 2011 00:14:42 +0100
> Petr Holasek <pholasek@redhat.com> wrote:
> 
> > On Thu, 01 Dec 2011, Andrew Morton wrote:
> > 
> > > On Thu,  1 Dec 2011 12:45:07 +0100
> > > Petr Holasek <pholasek@redhat.com> wrote:
> > > 
> > > > This patch adds constraints checks into __node_distance() and
> > > > numa_set_distance() functions. If from or to parameters are
> > > > lower than zero, it results into oops now.
> > > 
> > > Passing negative numbers into __node_distance() sounds like a bug in
> > > the caller, and this patch will remove our means of detecting that bug.
> > 
> > That's true, but upper boundary is checked now, so why not to check lower?
> 
> Because it adds more code to the kernel and can hide bugs?
> 
> > Seems inconsistent to me - from this point of view even don't check anything
> > would be better for detecting bug in the caller.
> > 
> > > 
> > > Perhaps we need to be told more about this patch.  Is the bug
> > > user-triggerable?  If so, how?  How was this fault triggered? 
> > > Etcetera.
> > > 
> > 
> > AFAIK, neither __node_distance() nor numa_set_distance() aren't in any
> > path from user-space inputs. Their paramaters are based on ACPI tables
> > provided by HW vendors.
> 
> That didn't answer my questions.  Have you observed any problems in
> this code?  If so, please fully describe them.  Or was it purely from
> code inspection?

Code inspection only, nothing from real life.

> 
> If what we're doing here is to be defensive against buggy BIOS tables
> (a good idea) then we should validate the BIOS table values as close as
> possible to the point where they were read frmo the BIOS.  And we should
> (probably) emit a warning if a bad table entry is detected, rather than
> silently fixing it up.

numa_set_distance() does exactly what you described above, only emits a
warning. I agree with your objections with __node_distance() checks, it
really can hide bugs in caller. So silent fix-up is the main problem and
we shouldn't check anything so the caller will be advised when using 
wrong nid by oops with a benefit of less code for us. Do I understand your
opinion on this type of code?

Re: NUMA x86: add constraints check for nid parameters

[David Rientjes]

On Fri, 2 Dec 2011, Petr Holasek wrote:

> > > > > This patch adds constraints checks into __node_distance() and
> > > > > numa_set_distance() functions. If from or to parameters are
> > > > > lower than zero, it results into oops now.
> > > > 
> > > > Passing negative numbers into __node_distance() sounds like a bug in
> > > > the caller, and this patch will remove our means of detecting that bug.
> > > 
> > > That's true, but upper boundary is checked now, so why not to check lower?
> > 
> > Because it adds more code to the kernel and can hide bugs?
> > 

The upper bound is checked to ensure that we don't dereference past end of 
the array that stores the distance table, so it will catch errors for 
things like memory hotplug when additional nodes are onlined and the data 
structure isn't updated accordingly.

> > If what we're doing here is to be defensive against buggy BIOS tables
> > (a good idea) then we should validate the BIOS table values as close as
> > possible to the point where they were read frmo the BIOS.  And we should
> > (probably) emit a warning if a bad table entry is detected, rather than
> > silently fixing it up.
> 
> numa_set_distance() does exactly what you described above, only emits a
> warning. I agree with your objections with __node_distance() checks, it
> really can hide bugs in caller. So silent fix-up is the main problem and
> we shouldn't check anything so the caller will be advised when using 
> wrong nid by oops with a benefit of less code for us. Do I understand your
> opinion on this type of code?

I'd have no objection to adding a check to numa_set_distance() to ensure 
the node ids are non-negative in the same way we check that the distances 
themselves are non-negative; that can catch errors when pxms are used 
uninitialized when parsing the SRAT.  However, I think adding the check to 
__node_distance() is unnecessary.

Re: NUMA x86: add constraints check for nid parameters

[Petr Holasek]

On Tue, 06 Dec 2011, David Rientjes wrote:

> 
> On Fri, 2 Dec 2011, Petr Holasek wrote:
> 
> > > > > > This patch adds constraints checks into __node_distance() and
> > > > > > numa_set_distance() functions. If from or to parameters are
> > > > > > lower than zero, it results into oops now.
> > > > > 
> > > > > Passing negative numbers into __node_distance() sounds like a bug in
> > > > > the caller, and this patch will remove our means of detecting that bug.
> > > > 
> > > > That's true, but upper boundary is checked now, so why not to check lower?
> > > 
> > > Because it adds more code to the kernel and can hide bugs?
> > > 
> 
> The upper bound is checked to ensure that we don't dereference past end of 
> the array that stores the distance table, so it will catch errors for 
> things like memory hotplug when additional nodes are onlined and the data 
> structure isn't updated accordingly.

Thanks for clarification, I missed this case.

> 
> > > If what we're doing here is to be defensive against buggy BIOS tables
> > > (a good idea) then we should validate the BIOS table values as close as
> > > possible to the point where they were read frmo the BIOS.  And we should
> > > (probably) emit a warning if a bad table entry is detected, rather than
> > > silently fixing it up.
> > 
> > numa_set_distance() does exactly what you described above, only emits a
> > warning. I agree with your objections with __node_distance() checks, it
> > really can hide bugs in caller. So silent fix-up is the main problem and
> > we shouldn't check anything so the caller will be advised when using 
> > wrong nid by oops with a benefit of less code for us. Do I understand your
> > opinion on this type of code?
> 
> I'd have no objection to adding a check to numa_set_distance() to ensure 
> the node ids are non-negative in the same way we check that the distances 
> themselves are non-negative; that can catch errors when pxms are used 
> uninitialized when parsing the SRAT.  However, I think adding the check to 
> __node_distance() is unnecessary.

Ok, I'll try v2 without __node_distance()

[PATCH v2] NUMA x86: add constraints check for nid parameters

[Petr Holasek]

This patch adds constraints checks for numa_set_distance()
function. It emits warning when pxms are used uninitialized
when parsing the SRAT.

Signed-off-by: Petr Holasek <pholasek@redhat.com>
---
 arch/x86/mm/numa.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index fbeaaf4..42c12b6 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -430,8 +430,9 @@ static int __init numa_alloc_distance(void)
  * calls are ignored until the distance table is reset with
  * numa_reset_distance().
  *
- * If @from or @to is higher than the highest known node at the time of
- * table creation or @distance doesn't make sense, the call is ignored.
+ * If @from or @to is higher than the highest known node or lower than zero
+ * at the time of table creation or @distance doesn't make sense, the call
+ * is ignored.
  * This is to allow simplification of specific NUMA config implementations.
  */
 void __init numa_set_distance(int from, int to, int distance)
@@ -439,7 +440,8 @@ void __init numa_set_distance(int from, int to, int distance)
 	if (!numa_distance && numa_alloc_distance() < 0)
 		return;
 
-	if (from >= numa_distance_cnt || to >= numa_distance_cnt) {
+	if (from >= numa_distance_cnt || to >= numa_distance_cnt ||
+			from < 0 || to < 0) {
 		printk_once(KERN_DEBUG "NUMA: Debug: distance out of bound, from=%d to=%d distance=%d\n",
 			    from, to, distance);
 		return;
-- 
1.7.6.4

Re: [PATCH v2] NUMA x86: add constraints check for nid parameters

[David Rientjes]

On Wed, 7 Dec 2011, Petr Holasek wrote:

> This patch adds constraints checks for numa_set_distance()
> function. It emits warning when pxms are used uninitialized
> when parsing the SRAT.
> 

The changelog also needs to indicate that, in addition to emitting the 
warning, that this will avoid a store to a negative index in the 
numa_distance[] array, that's the real thing you're trying to catch.  This 
would happen if pxm_to_node() is returning NUMA_NO_NODE which is what the 
pxm-to-node mapping is initialized to.

> Signed-off-by: Petr Holasek <pholasek@redhat.com>
> ---
>  arch/x86/mm/numa.c |    8 +++++---
>  1 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> index fbeaaf4..42c12b6 100644
> --- a/arch/x86/mm/numa.c
> +++ b/arch/x86/mm/numa.c
> @@ -430,8 +430,9 @@ static int __init numa_alloc_distance(void)
>   * calls are ignored until the distance table is reset with
>   * numa_reset_distance().
>   *
> - * If @from or @to is higher than the highest known node at the time of
> - * table creation or @distance doesn't make sense, the call is ignored.
> + * If @from or @to is higher than the highest known node or lower than zero
> + * at the time of table creation or @distance doesn't make sense, the call
> + * is ignored.
>   * This is to allow simplification of specific NUMA config implementations.
>   */
>  void __init numa_set_distance(int from, int to, int distance)
> @@ -439,7 +440,8 @@ void __init numa_set_distance(int from, int to, int distance)
>  	if (!numa_distance && numa_alloc_distance() < 0)
>  		return;
>  
> -	if (from >= numa_distance_cnt || to >= numa_distance_cnt) {
> +	if (from >= numa_distance_cnt || to >= numa_distance_cnt ||
> +			from < 0 || to < 0) {
>  		printk_once(KERN_DEBUG "NUMA: Debug: distance out of bound, from=%d to=%d distance=%d\n",
>  			    from, to, distance);

That warning doesn't look appropriate for negative node ids, it should be 
modified to say the node ids or distance are out of bounds.  One more 
revision?

>  		return;

[PATCH v3] NUMA x86: add constraints check for nid parameters

[Petr Holasek]

This patch adds constraints checks for numa_set_distance()
function. It emits warning and avoids a store to a negative
index in numa_distance[] array. Negative ids can be passed when
pxm-to-nids mapping is not properly filled while parsing the SRAT.

Signed-off-by: Petr Holasek <pholasek@redhat.com>
---
 arch/x86/mm/numa.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index fbeaaf4..cdc0054 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -430,8 +430,9 @@ static int __init numa_alloc_distance(void)
  * calls are ignored until the distance table is reset with
  * numa_reset_distance().
  *
- * If @from or @to is higher than the highest known node at the time of
- * table creation or @distance doesn't make sense, the call is ignored.
+ * If @from or @to is higher than the highest known node or lower than zero
+ * at the time of table creation or @distance doesn't make sense, the call
+ * is ignored.
  * This is to allow simplification of specific NUMA config implementations.
  */
 void __init numa_set_distance(int from, int to, int distance)
@@ -439,8 +440,9 @@ void __init numa_set_distance(int from, int to, int distance)
 	if (!numa_distance && numa_alloc_distance() < 0)
 		return;
 
-	if (from >= numa_distance_cnt || to >= numa_distance_cnt) {
-		printk_once(KERN_DEBUG "NUMA: Debug: distance out of bound, from=%d to=%d distance=%d\n",
+	if (from >= numa_distance_cnt || to >= numa_distance_cnt ||
+			from < 0 || to < 0) {
+		pr_warn_once("NUMA: Warning: node ids are out of bound, from=%d to=%d distance=%d\n",
 			    from, to, distance);
 		return;
 	}
-- 
1.7.6.4

Re: [PATCH v3] NUMA x86: add constraints check for nid parameters

[David Rientjes]

On Thu, 8 Dec 2011, Petr Holasek wrote:

> This patch adds constraints checks for numa_set_distance()
> function. It emits warning and avoids a store to a negative
> index in numa_distance[] array. Negative ids can be passed when
> pxm-to-nids mapping is not properly filled while parsing the SRAT.
> 
> Signed-off-by: Petr Holasek <pholasek@redhat.com>

Acked-by: David Rientjes <rientjes@google.com>

Thanks Petr!

Re: [PATCH v3] NUMA x86: add constraints check for nid parameters

[Ingo Molnar]

* David Rientjes <rientjes@google.com> wrote:

> On Thu, 8 Dec 2011, Petr Holasek wrote:
> 
> > This patch adds constraints checks for numa_set_distance()
> > function. It emits warning and avoids a store to a negative
> > index in numa_distance[] array. Negative ids can be passed when
> > pxm-to-nids mapping is not properly filled while parsing the SRAT.
> > 
> > Signed-off-by: Petr Holasek <pholasek@redhat.com>
> 
> Acked-by: David Rientjes <rientjes@google.com>

Thanks guys.

Just to double check: there's no known instance of such a bad 
SRAT in existence, so this commit can wait until v3.3 and does 
hot have to go into v3.2, right?

Thanks,

	Ingo

Re: [PATCH v3] NUMA x86: add constraints check for nid parameters

[David Rientjes]

On Fri, 9 Dec 2011, Ingo Molnar wrote:

> Thanks guys.
> 
> Just to double check: there's no known instance of such a bad 
> SRAT in existence, so this commit can wait until v3.3 and does 
> hot have to go into v3.2, right?
> 

Andi mentioned buggy SRATs, but it's outside the scope of this patch; this 
has nothing to do with buggy SRATs.

Ignoring NUMA emulation which plays with these when you boot with 
numa=fake, this patch is catching any instance where pxm_to_node(x) 
returns NUMA_NO_NODE, meaning x is not an initialized pxm.  For x86, we 
initialize pxms by grabbing them from the SRAT, picking the first unused 
node id, and mapping them.  The SRAT has nothing to do with this, the ACPI 
spec has no notion of what we've defined a node to be.  So Petr's patch 
will simply catch any instance of pxm_to_node(x) where x was not 
initialized and incorrectly referencing 

[tip:x86/mm] x86/numa: Add constraints check for nid parameters

[tip-bot for Petr Holasek]

Commit-ID:  54eed6cb16ec315565aaaf8e34252ca253a68b7b
Gitweb:     http://git.kernel.org/tip/54eed6cb16ec315565aaaf8e34252ca253a68b7b
Author:     Petr Holasek <pholasek@redhat.com>
AuthorDate: Thu, 8 Dec 2011 13:16:41 +0100
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 9 Dec 2011 08:03:34 +0100

x86/numa: Add constraints check for nid parameters

This patch adds constraint checks to the numa_set_distance()
function.

When the check triggers (this should not happen normally) it
emits a warning and avoids a store to a negative index in
numa_distance[] array - i.e. avoids memory corruption.

Negative ids can be passed when the pxm-to-nids mapping is not
properly filled while parsing the SRAT.

Signed-off-by: Petr Holasek <pholasek@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Anton Arapov <anton@redhat.com>
Link: http://lkml.kernel.org/r/20111208121640.GA2229@dhcp-27-244.brq.redhat.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/mm/numa.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index fbeaaf4..cdc0054 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -430,8 +430,9 @@ static int __init numa_alloc_distance(void)
  * calls are ignored until the distance table is reset with
  * numa_reset_distance().
  *
- * If @from or @to is higher than the highest known node at the time of
- * table creation or @distance doesn't make sense, the call is ignored.
+ * If @from or @to is higher than the highest known node or lower than zero
+ * at the time of table creation or @distance doesn't make sense, the call
+ * is ignored.
  * This is to allow simplification of specific NUMA config implementations.
  */
 void __init numa_set_distance(int from, int to, int distance)
@@ -439,8 +440,9 @@ void __init numa_set_distance(int from, int to, int distance)
 	if (!numa_distance && numa_alloc_distance() < 0)
 		return;
 
-	if (from >= numa_distance_cnt || to >= numa_distance_cnt) {
-		printk_once(KERN_DEBUG "NUMA: Debug: distance out of bound, from=%d to=%d distance=%d\n",
+	if (from >= numa_distance_cnt || to >= numa_distance_cnt ||
+			from < 0 || to < 0) {
+		pr_warn_once("NUMA: Warning: node ids are out of bound, from=%d to=%d distance=%d\n",
 			    from, to, distance);
 		return;
 	}

Re: [PATCH v2] NUMA x86: add constraints check for nid parameters

[Andi Kleen]

Petr Holasek <pholasek@redhat.com> writes:

> This patch adds constraints checks for numa_set_distance()
> function. It emits warning when pxms are used uninitialized
> when parsing the SRAT.

Can you expand on the motivation for this please?
Is this to catch buggy code or to catch buggy SRATs?
If the later are they actually out there?

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only

Re: [PATCH v2] NUMA x86: add constraints check for nid parameters

[David Rientjes]

On Thu, 8 Dec 2011, Andi Kleen wrote:

> > This patch adds constraints checks for numa_set_distance()
> > function. It emits warning when pxms are used uninitialized
> > when parsing the SRAT.
> 
> Can you expand on the motivation for this please?

It's adding a debugging check if something erroneously passes a negative 
node id when setting a distance, perhaps because of buggy code that failed 
to initialize the pxm-to-node mapping correctly which would result in 
storing to a negative index of the numa_distance array as indicated in the 
changelog.  It's for robustness and to warn explicitly rather than 
silently rejecting it unless you're monitoring debug output.

Re: [PATCH v2] NUMA x86: add constraints check for nid parameters

[Ingo Molnar]

* Andi Kleen <andi@firstfloor.org> wrote:

> Petr Holasek <pholasek@redhat.com> writes:
> 
> > This patch adds constraints checks for numa_set_distance()
> > function. It emits warning when pxms are used uninitialized
> > when parsing the SRAT.
> 
> Can you expand on the motivation for this please?
> Is this to catch buggy code or to catch buggy SRATs?

Both.

> If the later are they actually out there?

Not that i know of - they would likely not boot Linux very well 
today.

Thanks,

	Ingo