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

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Message-ID: <aSTT0gbH-NkDOH8A@alpha.franken.de>
Date: Mon, 24 Nov 2025 22:53:22 +0100
From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To: Gregory CLEMENT <gregory.clement@...tlin.com>
Cc: torvalds@...ux-foundation.org, linux-mips@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] MIPS fixes for v6.18

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.

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

-- 
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