MIPS: mm: kmalloc tlb_vpn array to avoid stack overflow

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 an small array on the stack.

Fixes: 35ad7e1 ("MIPS: mm: tlb-r4k: Uniquify TLB entries on init")
Co-developed-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: stable@vger.kernel.org # v6.17+: 9f048fa: MIPS: mm: Prevent a TLB shutdown on initial uniquification
Cc: stable@vger.kernel.org # v6.17+
Tested-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Tested-by: Klara Modin <klarasmodin@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: tsbogend

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>
@@ -522,17 +523,26 @@ static int r4k_vpn_cmp(const void *a, const void *b)
  * Initialise all TLB entries with unique values that do not clash with
  * what we have been handed over and what we'll be using ourselves.
  */
-static void r4k_tlb_uniquify(void)
+static void __ref 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);
 }
 
 /*