linux-kernel - Re: [PATCH v2] MIPS: mm: kmalloc tlb

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Message-ID: <alpine.DEB.2.21.2511261847410.36486@angie.orcam.me.uk>
Date: Wed, 26 Nov 2025 18:52:07 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
cc: Jiaxun Yang <jiaxun.yang@...goat.com>, linux-mips@...r.kernel.org, 
    linux-kernel@...r.kernel.org, 
    Gregory CLEMENT <gregory.clement@...tlin.com>
Subject: Re: [PATCH v2] MIPS: mm: kmalloc tlb_vpn array to avoid stack
 overflow

On Tue, 25 Nov 2025, Thomas Bogendoerfer wrote:

> Latest MIPS cores could have much more than 64 TLB entries, therefore
> allocate array for unification instead of placing a too small array
> on stack.

 Hmm, I get:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at arch/mips/mm/tlb-r4k.c:540 tlb_init+0x2a0/0x4bc
Modules linked in:
CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.18.0-rc1-dirty #60 NONE
Hardware name: mti,malta
Stack : 00000000 00000004 00000000 0000001d 809d1d2c 00000000 00000100 80944048
        809d91bc 80944048 80a16a73 00000000 80b634a4 00000001 809d1ce0 809f7bc8
        00000000 00000000 80944048 0000001f 00000001 809d1c14 00000000 653a206d
        00000000 80b656d4 80b6570b 00000000 00000000 00000000 80944048 00000000
        00000000 0000021c 80a40000 00000000 00000000 00000020 00000000 800472a4
        ...
Call Trace:
[<80112bd8>] show_stack+0x28/0xf0
[<8010a69c>] dump_stack_lvl+0x48/0x7c
[<8012fedc>] __warn+0x9c/0x118
[<801015e8>] warn_slowpath_fmt+0x58/0xa4
[<8012ba84>] tlb_init+0x2a0/0x4bc
[<80114738>] per_cpu_trap_init+0x17c/0x27c
[<80a1d0f8>] trap_init+0xf0/0x794
[<80a19ae4>] start_kernel+0x3c4/0x598

---[ end trace 0000000000000000 ]---

exactly here:

> +	tlb_vpns = kmalloc_array(tlbsize, sizeof(unsigned long), GFP_KERNEL);
> +	if (WARN_ON(!tlb_vpns))
> +		return; /* Pray local_flush_tlb_all() is good enough. */

I'll try to find out more, but right now this doesn't appear to work.

  Maciej