[PATCH] arm64: cpufeature: Don't cpu_enable_mte() when KASAN_GENERIC is active

[Will Deacon]

On Thu, Oct 09, 2025 at 08:10:53AM +0900, Yunseong Kim wrote:
> To summarize my situation, I thought the boot panic issue might be due
> to incompatibility between MTE and KASAN Generic, so I sent this patch.
> 
> However, it seems that the problem is related to the call path involving
> ZERO page. Also, I am curious how it works correctly in other machine.
> 
> On 10/9/25 7:28 AM, Yunseong Kim wrote:
> > Hi Andrey,
> > 
> > On 10/9/25 6:36 AM, Andrey Konovalov wrote:
> >> On Wed, Oct 8, 2025 at 11:13 PM Yunseong Kim <ysk at kzalloc.com> wrote:
> >>> [...]
> >> I do not understand this. Why is Generic KASAN incompatible with MTE?
> > 
> > My board wouldn't boot on the debian debug kernel, so I enabled
> > earlycon=pl011,0x40d0000 and checked via the UART console.
> > 
> >> Running Generic KASAN in the kernel while having MTE enabled (and e.g.
> >> used in userspace) seems like a valid combination.
> > 
> > Then it must be caused by something else. Thank you for letting me know.
> > 
> > It seems to be occurring in the call path as follows:
> > 
> > cpu_enable_mte()
> >  -> try_page_mte_tagging(ZERO_PAGE(0))
> >    -> VM_WARN_ON_ONCE(folio_test_hugetlb(page_folio(page)));
> > 
> >  https://elixir.bootlin.com/linux/v6.17/source/arch/arm64/include/asm/mte.h#L83
> 
>  -> page_folio(ZERO_PAGE(0))
>   -> (struct folio *)_compound_head(ZERO_PAGE(0))
> 
>  https://elixir.bootlin.com/linux/v6.17/source/include/linux/page-flags.h#L307

Do you have:

https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=f620d66af3165838bfa845dcf9f5f9b4089bf508

?

Will