Commit 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")
adds functionality that architectures can use to optionally allocate and
build cacheinfo early during boot. Commit 6539cffa9495 ("cacheinfo: Add
arch specific early level initializer") lets secondary CPUs correct (and
reallocate memory) cacheinfo data if needed.
If the early build functionality is not used and cacheinfo does not need
correction, memory for cacheinfo is never allocated. x86 does not use the
early build functionality. Consequently, during the cacheinfo CPU hotplug
callback, last_level_cache_is_valid() attempts to dereference a NULL
pointer:
BUG: kernel NULL pointer dereference, address: 0000000000000100
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEPMT SMP NOPTI
CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1
RIP: 0010: last_level_cache_is_valid+0x95/0xe0a
Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback if
not done earlier.
Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Reviewed-by: Radu Rendec <rrendec@redhat.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Andreas Herrmann <aherrmann@suse.de>
Fixes: 6539cffa9495 ("cacheinfo: Add arch specific early level initializer")
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
Cc: Andreas Herrmann <aherrmann@suse.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chen Yu <yu.c.chen@intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Nikolay Borisov <nik.borisov@suse.com>
Cc: Radu Rendec <rrendec@redhat.com>
Cc: Pierre Gondois <Pierre.Gondois@arm.com>
Cc: Pu Wen <puwen@hygon.cn>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: stable@vger.kernel.org # 6.3+
---
The motivation for commit 5944ce092b97 was to prevent a BUG splat in
PREEMPT_RT kernels during memory allocation. This splat is not observed on
x86 because the memory allocation for cacheinfo happens in
detect_cache_attributes() from the cacheinfo CPU hotplug callback.
The dereference of a NULL pointer is not observed today because
cache_leaves(cpu) is zero until after init_cache_level() is called (also
during the CPU hotplug callback). A subsequent changeset will set the
number of cache leaves earlier and the NULL-pointer dereference will be
observed.
---
Changes since v5:
* Fixed nonsensical subject (Nikolay).
* Added Reviewed-by tag from Nikolay and Andreas. Thanks!
* Added Tested-by tag from Andreas. Thanks!
Changes since v4:
* None
Changes since v3:
* Added Reviewed-by tag from Radu and Sudeep. Thanks!
Changes since v2:
* Introduced this patch.
Changes since v1:
* N/A
---
drivers/base/cacheinfo.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 77f2e0f91589..0332148691f9 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -554,7 +554,11 @@ static inline int init_level_allocate_ci(unsigned int cpu)
*/
ci_cacheinfo(cpu)->early_ci_levels = false;
- if (cache_leaves(cpu) <= early_leaves)
+ /*
+ * Some architectures (e.g., x86) do not use early initialization.
+ * Allocate memory now in such case.
+ */
+ if (cache_leaves(cpu) <= early_leaves && per_cpu_cacheinfo(cpu))
return 0;
kfree(per_cpu_cacheinfo(cpu));
--
2.34.1On Wed, Sep 04, 2024 at 11:00:34PM -0700, Ricardo Neri wrote:
> Commit 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")
> adds functionality that architectures can use to optionally allocate and
> build cacheinfo early during boot. Commit 6539cffa9495 ("cacheinfo: Add
> arch specific early level initializer") lets secondary CPUs correct (and
> reallocate memory) cacheinfo data if needed.
>
> If the early build functionality is not used and cacheinfo does not need
> correction, memory for cacheinfo is never allocated. x86 does not use the
> early build functionality. Consequently, during the cacheinfo CPU hotplug
> callback, last_level_cache_is_valid() attempts to dereference a NULL
> pointer:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000100
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not present page
> PGD 0 P4D 0
> Oops: 0000 [#1] PREEPMT SMP NOPTI
> CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1
> RIP: 0010: last_level_cache_is_valid+0x95/0xe0a
>
> Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback if
> not done earlier.
Why is this a separate patch?
It sounds like it should be merged with the first one as both address a CPU
hotplug issue AFAICT.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
On Wed, Sep 11, 2024 at 04:08:44PM +0200, Borislav Petkov wrote:
> On Wed, Sep 04, 2024 at 11:00:34PM -0700, Ricardo Neri wrote:
> > Commit 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")
> > adds functionality that architectures can use to optionally allocate and
> > build cacheinfo early during boot. Commit 6539cffa9495 ("cacheinfo: Add
> > arch specific early level initializer") lets secondary CPUs correct (and
> > reallocate memory) cacheinfo data if needed.
> >
> > If the early build functionality is not used and cacheinfo does not need
> > correction, memory for cacheinfo is never allocated. x86 does not use the
> > early build functionality. Consequently, during the cacheinfo CPU hotplug
> > callback, last_level_cache_is_valid() attempts to dereference a NULL
> > pointer:
> >
> > BUG: kernel NULL pointer dereference, address: 0000000000000100
> > #PF: supervisor read access in kernel mode
> > #PF: error_code(0x0000) - not present page
> > PGD 0 P4D 0
> > Oops: 0000 [#1] PREEPMT SMP NOPTI
> > CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1
> > RIP: 0010: last_level_cache_is_valid+0x95/0xe0a
> >
> > Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback if
> > not done earlier.
>
> Why is this a separate patch?
>
> It sounds like it should be merged with the first one as both address a CPU
> hotplug issue AFAICT.
Thank you for your review Borislav!
Yes, both patches address issues during CPU hotplug (both NULL-pointer
dereference). However, IHMO, they are separate issues. Patch 1/4 fixes
a missing allocation check. Patch 2/4 causes the allocation to happen in
case early allocation is not used.
If I did not convince you, I am happy to merge together patches 1 and 2.
Thanks and BR,
Ricardo
On Wed, Sep 11, 2024 at 04:34:10PM -0700, Ricardo Neri wrote:
> Yes, both patches address issues during CPU hotplug (both NULL-pointer
> dereference). However, IHMO, they are separate issues. Patch 1/4 fixes
> a missing allocation check. Patch 2/4 causes the allocation to happen in
> case early allocation is not used.
>
> If I did not convince you, I am happy to merge together patches 1 and 2.
Well, what is easier to handle by stable and/or backporters: one patch or two
patches fixing two very similar CPU hotplug isuses in cacheinfo?
IOW, what is the benefit in having two patches instead of one?
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
On Thu, Sep 12, 2024 at 12:59:18PM +0200, Borislav Petkov wrote: > On Wed, Sep 11, 2024 at 04:34:10PM -0700, Ricardo Neri wrote: > > Yes, both patches address issues during CPU hotplug (both NULL-pointer > > dereference). However, IHMO, they are separate issues. Patch 1/4 fixes > > a missing allocation check. Patch 2/4 causes the allocation to happen in > > case early allocation is not used. > > > > If I did not convince you, I am happy to merge together patches 1 and 2. > > Well, what is easier to handle by stable and/or backporters: one patch or two > patches fixing two very similar CPU hotplug isuses in cacheinfo? Indeed, one patch would be easier to handle. > > IOW, what is the benefit in having two patches instead of one? Marginal I guess. I can put all the background and rationale in the commit message. I will post a new version merging patches 1 and 2... and fixing the formatting of allocate_cache_info().
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