[PATCH v3] x86/mce: Dynamically size space for machine check records

[PATCH v3] x86/mce: Dynamically size space for machine check records

[Tony Luck]

Systems with a large number of CPUs may generate a large
number of machine check records when things go seriously
wrong. But Linux has a fixed buffer that can only capture
a few dozen errors.

Allocate space based on the number of CPUs (with a minimum
value based on the historical fixed buffer that could store
80 records).

Signed-off-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
---

Changes since V2; Link: https://lore.kernel.org/all/20240307000256.34352-1-tony.luck@intel.com/

Boris: Eliminate "out:" label in mce_gen_pool_create()

Sohil: Added Reviewed-by tag

 arch/x86/kernel/cpu/mce/genpool.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/genpool.c b/arch/x86/kernel/cpu/mce/genpool.c
index fbe8b61c3413..cadf28662a70 100644
--- a/arch/x86/kernel/cpu/mce/genpool.c
+++ b/arch/x86/kernel/cpu/mce/genpool.c
@@ -16,14 +16,14 @@
  * used to save error information organized in a lock-less list.
  *
  * This memory pool is only to be used to save MCE records in MCE context.
- * MCE events are rare, so a fixed size memory pool should be enough. Use
- * 2 pages to save MCE events for now (~80 MCE records at most).
+ * MCE events are rare, so a fixed size memory pool should be enough.
+ * Allocate on a sliding scale based on number of CPUs.
  */
-#define MCE_POOLSZ	(2 * PAGE_SIZE)
+#define MCE_MIN_ENTRIES	80
+#define MCE_PER_CPU	2
 
 static struct gen_pool *mce_evt_pool;
 static LLIST_HEAD(mce_event_llist);
-static char gen_pool_buf[MCE_POOLSZ];
 
 /*
  * Compare the record "t" with each of the records on list "l" to see if
@@ -118,22 +118,32 @@ int mce_gen_pool_add(struct mce *mce)
 
 static int mce_gen_pool_create(void)
 {
+	int mce_numrecords, mce_poolsz, order;
 	struct gen_pool *tmpp;
 	int ret = -ENOMEM;
+	void *mce_pool;
 
-	tmpp = gen_pool_create(ilog2(sizeof(struct mce_evt_llist)), -1);
+	order = order_base_2(sizeof(struct mce_evt_llist));
+	tmpp = gen_pool_create(order, -1);
 	if (!tmpp)
-		goto out;
+		return ret;
 
-	ret = gen_pool_add(tmpp, (unsigned long)gen_pool_buf, MCE_POOLSZ, -1);
+	mce_numrecords = max(MCE_MIN_ENTRIES, num_possible_cpus() * MCE_PER_CPU);
+	mce_poolsz = mce_numrecords * (1 << order);
+	mce_pool = kmalloc(mce_poolsz, GFP_KERNEL);
+	if (!mce_pool) {
+		gen_pool_destroy(tmpp);
+		return ret;
+	}
+	ret = gen_pool_add(tmpp, (unsigned long)mce_pool, mce_poolsz, -1);
 	if (ret) {
 		gen_pool_destroy(tmpp);
-		goto out;
+		kfree(mce_pool);
+		return ret;
 	}
 
 	mce_evt_pool = tmpp;
 
-out:
 	return ret;
 }
 

base-commit: d206a76d7d2726f3b096037f2079ce0bd3ba329b
-- 
2.43.0

Re: [PATCH v3] x86/mce: Dynamically size space for machine check records

[Naik, Avadhut]

On 3/7/2024 13:27, Tony Luck wrote:
> Systems with a large number of CPUs may generate a large
> number of machine check records when things go seriously
> wrong. But Linux has a fixed buffer that can only capture
> a few dozen errors.
> 
> Allocate space based on the number of CPUs (with a minimum
> value based on the historical fixed buffer that could store
> 80 records).
> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
> ---
> 
> Changes since V2; Link: https://lore.kernel.org/all/20240307000256.34352-1-tony.luck@intel.com/
> 
> Boris: Eliminate "out:" label in mce_gen_pool_create()
> 
> Sohil: Added Reviewed-by tag
> 
>  arch/x86/kernel/cpu/mce/genpool.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/genpool.c b/arch/x86/kernel/cpu/mce/genpool.c
> index fbe8b61c3413..cadf28662a70 100644
> --- a/arch/x86/kernel/cpu/mce/genpool.c
> +++ b/arch/x86/kernel/cpu/mce/genpool.c
> @@ -16,14 +16,14 @@
>   * used to save error information organized in a lock-less list.
>   *
>   * This memory pool is only to be used to save MCE records in MCE context.
> - * MCE events are rare, so a fixed size memory pool should be enough. Use
> - * 2 pages to save MCE events for now (~80 MCE records at most).
> + * MCE events are rare, so a fixed size memory pool should be enough.
> + * Allocate on a sliding scale based on number of CPUs.
>   */
> -#define MCE_POOLSZ	(2 * PAGE_SIZE)
> +#define MCE_MIN_ENTRIES	80
> +#define MCE_PER_CPU	2
>  
>  static struct gen_pool *mce_evt_pool;
>  static LLIST_HEAD(mce_event_llist);
> -static char gen_pool_buf[MCE_POOLSZ];
>  
>  /*
>   * Compare the record "t" with each of the records on list "l" to see if
> @@ -118,22 +118,32 @@ int mce_gen_pool_add(struct mce *mce)
>  
>  static int mce_gen_pool_create(void)
>  {
> +	int mce_numrecords, mce_poolsz, order;
>  	struct gen_pool *tmpp;
>  	int ret = -ENOMEM;
> +	void *mce_pool;
>  
> -	tmpp = gen_pool_create(ilog2(sizeof(struct mce_evt_llist)), -1);
> +	order = order_base_2(sizeof(struct mce_evt_llist));
> +	tmpp = gen_pool_create(order, -1);
>  	if (!tmpp)
> -		goto out;
> +		return ret;
>  
> -	ret = gen_pool_add(tmpp, (unsigned long)gen_pool_buf, MCE_POOLSZ, -1);
> +	mce_numrecords = max(MCE_MIN_ENTRIES, num_possible_cpus() * MCE_PER_CPU);
> +	mce_poolsz = mce_numrecords * (1 << order);
> +	mce_pool = kmalloc(mce_poolsz, GFP_KERNEL);
> +	if (!mce_pool) {
> +		gen_pool_destroy(tmpp);
> +		return ret;
> +	}
> +	ret = gen_pool_add(tmpp, (unsigned long)mce_pool, mce_poolsz, -1);
>  	if (ret) {
>  		gen_pool_destroy(tmpp);
> -		goto out;
> +		kfree(mce_pool);
> +		return ret;
>  	}
>  
>  	mce_evt_pool = tmpp;
>  
> -out:
>  	return ret;
>  }
>  
> 
> base-commit: d206a76d7d2726f3b096037f2079ce0bd3ba329b

LGTM!

Reviewed-by: Avadhut Naik <avadhut.naik@amd.com>

-- 
Thanks,
Avadhut Naik

Re: [PATCH v3] x86/mce: Dynamically size space for machine check records

[Borislav Petkov]

On Thu, Mar 07, 2024 at 11:27:04AM -0800, Tony Luck wrote:
> -	ret = gen_pool_add(tmpp, (unsigned long)gen_pool_buf, MCE_POOLSZ, -1);
> +	mce_numrecords = max(MCE_MIN_ENTRIES, num_possible_cpus() * MCE_PER_CPU);
> +	mce_poolsz = mce_numrecords * (1 << order);

So, on a big fat machine with 8K CPUs that's, what

	8192 * 2 * (1 << 8) = ~4M

buffer?

Well, if you have a fat machine, you get fat buffers too.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

[tip: ras/core] x86/mce: Dynamically size space for machine check records

[tip-bot2 for Tony Luck]

The following commit has been merged into the ras/core branch of tip:

Commit-ID:     108c6494bdf1dfeaefc0a506e2f471aa92fafdd6
Gitweb:        https://git.kernel.org/tip/108c6494bdf1dfeaefc0a506e2f471aa92fafdd6
Author:        Tony Luck <tony.luck@intel.com>
AuthorDate:    Thu, 07 Mar 2024 11:27:04 -08:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 26 Mar 2024 12:40:42 +01:00

x86/mce: Dynamically size space for machine check records

Systems with a large number of CPUs may generate a large number of
machine check records when things go seriously wrong. But Linux has
a fixed-size buffer that can only capture a few dozen errors.

Allocate space based on the number of CPUs (with a minimum value based
on the historical fixed buffer that could store 80 records).

  [ bp: Rename local var from tmpp to something more telling: gpool. ]

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Reviewed-by: Avadhut Naik <avadhut.naik@amd.com>
Link: https://lore.kernel.org/r/20240307192704.37213-1-tony.luck@intel.com
---
 arch/x86/kernel/cpu/mce/genpool.c | 40 ++++++++++++++++++------------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/genpool.c b/arch/x86/kernel/cpu/mce/genpool.c
index fbe8b61..4284749 100644
--- a/arch/x86/kernel/cpu/mce/genpool.c
+++ b/arch/x86/kernel/cpu/mce/genpool.c
@@ -16,14 +16,14 @@
  * used to save error information organized in a lock-less list.
  *
  * This memory pool is only to be used to save MCE records in MCE context.
- * MCE events are rare, so a fixed size memory pool should be enough. Use
- * 2 pages to save MCE events for now (~80 MCE records at most).
+ * MCE events are rare, so a fixed size memory pool should be enough.
+ * Allocate on a sliding scale based on number of CPUs.
  */
-#define MCE_POOLSZ	(2 * PAGE_SIZE)
+#define MCE_MIN_ENTRIES	80
+#define MCE_PER_CPU	2
 
 static struct gen_pool *mce_evt_pool;
 static LLIST_HEAD(mce_event_llist);
-static char gen_pool_buf[MCE_POOLSZ];
 
 /*
  * Compare the record "t" with each of the records on list "l" to see if
@@ -118,22 +118,32 @@ int mce_gen_pool_add(struct mce *mce)
 
 static int mce_gen_pool_create(void)
 {
-	struct gen_pool *tmpp;
+	int mce_numrecords, mce_poolsz, order;
+	struct gen_pool *gpool;
 	int ret = -ENOMEM;
-
-	tmpp = gen_pool_create(ilog2(sizeof(struct mce_evt_llist)), -1);
-	if (!tmpp)
-		goto out;
-
-	ret = gen_pool_add(tmpp, (unsigned long)gen_pool_buf, MCE_POOLSZ, -1);
+	void *mce_pool;
+
+	order = order_base_2(sizeof(struct mce_evt_llist));
+	gpool = gen_pool_create(order, -1);
+	if (!gpool)
+		return ret;
+
+	mce_numrecords = max(MCE_MIN_ENTRIES, num_possible_cpus() * MCE_PER_CPU);
+	mce_poolsz = mce_numrecords * (1 << order);
+	mce_pool = kmalloc(mce_poolsz, GFP_KERNEL);
+	if (!mce_pool) {
+		gen_pool_destroy(gpool);
+		return ret;
+	}
+	ret = gen_pool_add(gpool, (unsigned long)mce_pool, mce_poolsz, -1);
 	if (ret) {
-		gen_pool_destroy(tmpp);
-		goto out;
+		gen_pool_destroy(gpool);
+		kfree(mce_pool);
+		return ret;
 	}
 
-	mce_evt_pool = tmpp;
+	mce_evt_pool = gpool;
 
-out:
 	return ret;
 }