linux-kernel - Re: [GIT PULL] MIPS fixes for v6.18

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Message-ID: <87tsyi8lsm.fsf@BLaptop.bootlin.com>
Date: Tue, 25 Nov 2025 11:10:49 +0100
From: Gregory CLEMENT <gregory.clement@...tlin.com>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: torvalds@...ux-foundation.org, linux-mips@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] MIPS fixes for v6.18

Hello Thomas,

> On Mon, Nov 24, 2025 at 04:46:44PM +0100, Gregory CLEMENT wrote:
>> Hello Thomas,
>> 
>> > The following changes since commit e9a6fb0bcdd7609be6969112f3fbfcce3b1d4a7c:
>> >
>> >   Linux 6.18-rc5 (2025-11-09 15:10:19 -0800)
>> >
>> > are available in the Git repository at:
>> >
>> >   git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux.git/ tags/mips-fixes_6.18_1
>> >
>> > for you to fetch changes up to 14b46ba92bf547508b4a49370c99aba76cb53b53:
>> >
>> >   MIPS: kernel: Fix random segmentation faults (2025-11-21 13:24:05 +0100)
>> >
>> > ----------------------------------------------------------------
>> > - Fix CPU type in DT for econet
>> > - Fix for Malta PCI MMIO breakage for SOC-it
>> > - Fix TLB shutdown caused by iniital uniquification
>> > - Fix random seg faults
>> >
>> > ----------------------------------------------------------------
>> > Aleksander Jan Bajkowski (1):
>> >       mips: dts: econet: fix EN751221 core type
>> >
>> > Maciej W. Rozycki (2):
>> >       MIPS: Malta: Fix !EVA SOC-it PCI MMIO
>> >       MIPS: mm: Prevent a TLB shutdown on initial uniquification
>> 
>> Today, the kernel v6.18-rc7 no longer boots on EyeQ5 and EyeQ6H (MIPS
>> I6500)-based boards. After a git bisect between v6.18-rc6 and v6.18-rc7,
>> we found that the culprit is the commit "MIPS: mm: Prevent a TLB
>> shutdown on initial uniquification".
>> 
>> Here is the log from a vanilla v6.18-rc7:
>
> [..]
>
> I guess your cores have more than 64 TLB entries. The Octeon CPU has
> 256 entries... Patch below fixes the issue there.
>

I have applied this patch and tested it on EyeQ5 and EyeQ6H-based
boards, and it booted successfully.

you can add my

Tested-by: Gregory CLEMENT <gregory.clement@...tlin.com>

Thanks,

Gregory

> Thomas.
>
> From b74abcb21103519ae48726c715d39a6aa3f57462 Mon Sep 17 00:00:00 2001
> From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Date: Mon, 24 Nov 2025 22:46:43 +0100
> Subject: [PATCH] MIPS: mm: kmalloc tlb_vpn array to avoid stack overflow
>
> 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.
>
> Fixes: 9f048fa48740 ("MIPS: mm: Prevent a TLB shutdown on initial uniquification")
> Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> ---
>  arch/mips/mm/tlb-r4k.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/mm/tlb-r4k.c b/arch/mips/mm/tlb-r4k.c
> index 3facf7cc6c7d..577055b50c41 100644
> --- a/arch/mips/mm/tlb-r4k.c
> +++ b/arch/mips/mm/tlb-r4k.c
> @@ -524,15 +524,19 @@ static int r4k_vpn_cmp(const void *a, const void *b)
>   */
>  static void r4k_tlb_uniquify(void)
>  {
> -	unsigned long tlb_vpns[1 << MIPS_CONF1_TLBS_SIZE];
>  	int tlbsize = current_cpu_data.tlbsize;
>  	int start = num_wired_entries();
> +	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_vpns = kmalloc_array(tlbsize, sizeof(unsigned long), GFP_KERNEL);
> +	if (!tlb_vpns)
> +		return; /* pray local_flush_tlb_all() is good enough */
> +
>  	htw_stop();
>  
>  	for (i = start, cnt = 0; i < tlbsize; i++, cnt++) {
> @@ -585,6 +589,7 @@ static void r4k_tlb_uniquify(void)
>  	tlbw_use_hazard();
>  	htw_start();
>  	flush_micro_tlb();
> +	kfree(tlb_vpns);
>  }
>  
>  /*
> -- 
> 2.43.0
>
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]

-- 
Grégory CLEMENT, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com