linux-kernel - Re: [PATCH 2/2] x86/MCE: Add command line option to extend MCE Records pool

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Date: Mon, 12 Feb 2024 13:37:09 -0800
From: Tony Luck <tony.luck@...el.com>
To: Borislav Petkov <bp@...en8.de>
Cc: "Naik, Avadhut" <avadnaik@....com>,
	"Mehta, Sohil" <sohil.mehta@...el.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"yazen.ghannam@....com" <yazen.ghannam@....com>,
	Avadhut Naik <avadhut.naik@....com>
Subject: Re: [PATCH 2/2] x86/MCE: Add command line option to extend MCE
 Records pool

On Mon, Feb 12, 2024 at 07:41:03PM +0000, Luck, Tony wrote:
> > It needs a proper explanation why that's ok rather than an empirical
> > test only.
> 
> start_kernel()
>    ... setup_arch()
>        .... acpi stuff parses MADT and sets bits in possible map
> 
>    ... arch_cpu_finalize_init()
>        ... calls mce_gen_pool_init()

This made me question the "we don't have an allocator in
mce_gen_pool_init()". Because if we got through all the
ACPI stuff, we surely have an allocator.

Below patch doesn't explode at runtime.

-Tony

diff --git a/arch/x86/kernel/cpu/mce/genpool.c b/arch/x86/kernel/cpu/mce/genpool.c
index fbe8b61c3413..81de877f2a51 100644
--- a/arch/x86/kernel/cpu/mce/genpool.c
+++ b/arch/x86/kernel/cpu/mce/genpool.c
@@ -16,14 +16,12 @@
  * 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)
 
 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
@@ -118,14 +116,23 @@ int mce_gen_pool_add(struct mce *mce)
 
 static int mce_gen_pool_create(void)
 {
+	int mce_numrecords, mce_poolsz;
 	struct gen_pool *tmpp;
 	int ret = -ENOMEM;
+	void *mce_pool;
 
 	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);
+	mce_numrecords = max(80, num_possible_cpus() * 8);
+	mce_poolsz = mce_numrecords * ilog2(sizeof(struct mce_evt_llist));
+	mce_pool = kmalloc(mce_poolsz, GFP_KERNEL);
+	if (!mce_pool) {
+		gen_pool_destroy(tmpp);
+		goto out;
+	}
+	ret = gen_pool_add(tmpp, (unsigned long)mce_pool, mce_poolsz, -1);
 	if (ret) {
 		gen_pool_destroy(tmpp);
 		goto out;
-- 
2.43.0