Re: [PATCH 6.6 000/389] 6.6.76-rc2 review

[Catalin Marinas <catalin.marinas@arm.com>]

On Wed, Feb 19, 2025 at 07:09:26PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Feb 19, 2025 at 05:18:24PM +0000, Catalin Marinas wrote:
> > The problem is in the arm64 arch_calc_vm_flag_bits() as it returns
> > VM_MTE_ALLOWED for any MAP_ANONYMOUS ignoring MAP_HUGETLB (it's been
> > doing this since day 1 of MTE). The implementation does handle the
> > hugetlb file mmap() correctly but not the MAP_ANONYMOUS case.
> > 
> > The fix would be something like below:
> > 
> > -----------------8<--------------------------
> > diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
> > index 5966ee4a6154..8ff5d88c9f12 100644
> > --- a/arch/arm64/include/asm/mman.h
> > +++ b/arch/arm64/include/asm/mman.h
> > @@ -28,7 +28,8 @@ static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
> >  	 * backed by tags-capable memory. The vm_flags may be overridden by a
> >  	 * filesystem supporting MTE (RAM-based).
> >  	 */
> > -	if (system_supports_mte() && (flags & MAP_ANONYMOUS))
> > +	if (system_supports_mte() &&
> > +	    ((flags & MAP_ANONYMOUS) && !(flags & MAP_HUGETLB)))
> >  		return VM_MTE_ALLOWED;
> > 
> >  	return 0;
> > -------------------8<-----------------------
> > 
> > This fix won't make sense for mainline since it supports MAP_HUGETLB
> > already.
> > 
> > Greg, are you ok with a stable-only fix as above or you'd rather see the
> > full 25c17c4b55de ("hugetlb: arm64: add mte support") backported?
> 
> A stable-only fix for this is fine, thanks!  Can you send it with a
> changelog and I'll queue it up.  Does it also need to go to older
> kernels as well?

5.10, that's when we got MTE support in. There may be some slight
variations depending on how far 5baf8b037deb ("mm: refactor
arch_calc_vm_flag_bits() and arm64 MTE handling") got backported. This
goes together with deb0f6562884 ("mm/mmap: undo ->mmap() when
arch_validate_flags() fails"), so they may actually go all the way to
5.10.

I'll prepare the patches tomorrow, give them a try and send to stable.

Thanks.

-- 
Catalin