FAILED: Patch "LoongArch: Disable instrumentation for setup_ptwalker()" failed to apply to 6.12-stable tree

FAILED: Patch "LoongArch: Disable instrumentation for setup_ptwalker()" failed to apply to 6.12-stable tree

[Sasha Levin]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 7cb37af61f09c9cfd90c43c9275307c16320cbf2 Mon Sep 17 00:00:00 2001
From: Tiezhu Yang <yangtiezhu@loongson.cn>
Date: Tue, 10 Feb 2026 19:31:17 +0800
Subject: [PATCH] LoongArch: Disable instrumentation for setup_ptwalker()

According to Documentation/dev-tools/kasan.rst, software KASAN modes use
compiler instrumentation to insert validity checks. Such instrumentation
might be incompatible with some parts of the kernel, and therefore needs
to be disabled, just use the attribute __no_sanitize_address to disable
instrumentation for the low level function setup_ptwalker().

Otherwise bringing up the secondary CPUs failed when CONFIG_KASAN is set
(especially when PTW is enabled), here are the call chains:

    smpboot_entry()
      start_secondary()
        cpu_probe()
          per_cpu_trap_init()
            tlb_init()
              setup_tlb_handler()
                setup_ptwalker()

The reason is the PGD registers are configured in setup_ptwalker(), but
KASAN instrumentation may cause TLB exceptions before that.

Cc: stable@vger.kernel.org
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
---
 arch/loongarch/mm/tlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/loongarch/mm/tlb.c b/arch/loongarch/mm/tlb.c
index 4014c44695878..aaf7d685cc2aa 100644
--- a/arch/loongarch/mm/tlb.c
+++ b/arch/loongarch/mm/tlb.c
@@ -202,7 +202,7 @@ void __update_tlb(struct vm_area_struct *vma, unsigned long address, pte_t *ptep
 	local_irq_restore(flags);
 }
 
-static void setup_ptwalker(void)
+static void __no_sanitize_address setup_ptwalker(void)
 {
 	unsigned long pwctl0, pwctl1;
 	unsigned long pgd_i = 0, pgd_w = 0;
-- 
2.51.0

Re: FAILED: Patch "LoongArch: Disable instrumentation for setup_ptwalker()" failed to apply to 6.12-stable tree

[Huacai Chen]

Hi, Sasha,

On Sun, Mar 1, 2026 at 9:27 AM Sasha Levin <sashal@kernel.org> wrote:
>
> The patch below does not apply to the 6.12-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
I'm very confused because it can be applied and already here:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/tree/queue-6.12

Huacai

>
> Thanks,
> Sasha
>
> ------------------ original commit in Linus's tree ------------------
>
> From 7cb37af61f09c9cfd90c43c9275307c16320cbf2 Mon Sep 17 00:00:00 2001
> From: Tiezhu Yang <yangtiezhu@loongson.cn>
> Date: Tue, 10 Feb 2026 19:31:17 +0800
> Subject: [PATCH] LoongArch: Disable instrumentation for setup_ptwalker()
>
> According to Documentation/dev-tools/kasan.rst, software KASAN modes use
> compiler instrumentation to insert validity checks. Such instrumentation
> might be incompatible with some parts of the kernel, and therefore needs
> to be disabled, just use the attribute __no_sanitize_address to disable
> instrumentation for the low level function setup_ptwalker().
>
> Otherwise bringing up the secondary CPUs failed when CONFIG_KASAN is set
> (especially when PTW is enabled), here are the call chains:
>
>     smpboot_entry()
>       start_secondary()
>         cpu_probe()
>           per_cpu_trap_init()
>             tlb_init()
>               setup_tlb_handler()
>                 setup_ptwalker()
>
> The reason is the PGD registers are configured in setup_ptwalker(), but
> KASAN instrumentation may cause TLB exceptions before that.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> ---
>  arch/loongarch/mm/tlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/mm/tlb.c b/arch/loongarch/mm/tlb.c
> index 4014c44695878..aaf7d685cc2aa 100644
> --- a/arch/loongarch/mm/tlb.c
> +++ b/arch/loongarch/mm/tlb.c
> @@ -202,7 +202,7 @@ void __update_tlb(struct vm_area_struct *vma, unsigned long address, pte_t *ptep
>         local_irq_restore(flags);
>  }
>
> -static void setup_ptwalker(void)
> +static void __no_sanitize_address setup_ptwalker(void)
>  {
>         unsigned long pwctl0, pwctl1;
>         unsigned long pgd_i = 0, pgd_w = 0;
> --
> 2.51.0
>
>
>
>
>