linux-kernel - [PATCH v3] MIPS: mm: kmalloc tlb_vpn array to avoid stack overflow

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Message-ID: <alpine.DEB.2.21.2511270406020.36486@angie.orcam.me.uk>
Date: Thu, 27 Nov 2025 04:54:10 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
cc: Jiaxun Yang <jiaxun.yang@...goat.com>, 
    Gregory CLEMENT <gregory.clement@...tlin.com>, linux-mips@...r.kernel.org, 
    linux-kernel@...r.kernel.org
Subject: [PATCH v3] MIPS: mm: kmalloc tlb_vpn array to avoid stack overflow

From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>

Owing to Config4.MMUSizeExt and VTLB/FTLB MMU features later MIPSr2+ 
cores can have more than 64 TLB entries.  Therefore allocate an array 
for uniquification instead of placing too small an array on the stack.

Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Signed-off-by: Maciej W. Rozycki <macro@...am.me.uk>
Fixes: 9f048fa48740 ("MIPS: mm: Prevent a TLB shutdown on initial uniquification")
Cc: stable@...r.kernel.org
---
 Verified with Malta/74Kf and Malta/interAptiv for initial and secondary 
CPU bootstrap.  The PM path hasn't been covered, but is expected to be 
the same as secondary CPU bootstrap.

 NB Malta/interAptiv has issues later on in SMP boot (boots fine UP) and 
hangs with repeated:

irq 23: nobody cared (try booting with the "irqpoll" option)
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.18.0-rc1-dirty #2 NONE

messages (for the CP0 timer interrupt AFAICT; GIC timer is supposed to 
be used instead).  This will have to be bisected.

Changes from v2:

- Use the bootmem allocator for early calls (CPU #0 bootstrap).

- Update the change description; mark for stable backporting.
---
 arch/mips/mm/tlb-r4k.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

linux-mips-tlb-r4k-uniquify-tlbsize.diff
Index: linux-macro/arch/mips/mm/tlb-r4k.c
===================================================================
--- linux-macro.orig/arch/mips/mm/tlb-r4k.c
+++ linux-macro/arch/mips/mm/tlb-r4k.c
@@ -12,6 +12,7 @@
 #include <linux/init.h>
 #include <linux/sched.h>
 #include <linux/smp.h>
+#include <linux/memblock.h>
 #include <linux/mm.h>
 #include <linux/hugetlb.h>
 #include <linux/export.h>
@@ -524,15 +525,24 @@ static int r4k_vpn_cmp(const void *a, co
  */
 static void r4k_tlb_uniquify(void)
 {
-	unsigned long tlb_vpns[1 << MIPS_CONF1_TLBS_SIZE];
 	int tlbsize = current_cpu_data.tlbsize;
+	bool use_slab = slab_is_available();
 	int start = num_wired_entries();
+	phys_addr_t tlb_vpn_size;
+	unsigned long *tlb_vpns;
 	unsigned long vpn_mask;
 	int cnt, ent, idx, i;
 
 	vpn_mask = GENMASK(cpu_vmbits - 1, 13);
 	vpn_mask |= IS_ENABLED(CONFIG_64BIT) ? 3ULL << 62 : 1 << 31;
 
+	tlb_vpn_size = tlbsize * sizeof(*tlb_vpns);
+	tlb_vpns = (use_slab ?
+		    kmalloc(tlb_vpn_size, GFP_KERNEL) :
+		    memblock_alloc_raw(tlb_vpn_size, sizeof(*tlb_vpns)));
+	if (WARN_ON(!tlb_vpns))
+		return; /* Pray local_flush_tlb_all() is good enough. */
+
 	htw_stop();
 
 	for (i = start, cnt = 0; i < tlbsize; i++, cnt++) {
@@ -585,6 +595,10 @@ static void r4k_tlb_uniquify(void)
 	tlbw_use_hazard();
 	htw_start();
 	flush_micro_tlb();
+	if (use_slab)
+		kfree(tlb_vpns);
+	else
+		memblock_free(tlb_vpns, tlb_vpn_size);
 }
 
 /*