Re: [PATCH hotfix 6.12 v4 4/5] mm: refactor arch_calc_vm_flag_bits() and arm64 MTE handling

[Vlastimil Babka <vbabka@suse.cz>]

On 10/30/24 11:58, Catalin Marinas wrote:
> On Wed, Oct 30, 2024 at 10:18:27AM +0100, Vlastimil Babka wrote:
>> On 10/29/24 19:11, Lorenzo Stoakes wrote:
>> > --- a/arch/arm64/include/asm/mman.h
>> > +++ b/arch/arm64/include/asm/mman.h
>> > @@ -6,6 +6,8 @@
>> > 
>> >  #ifndef BUILD_VDSO
>> >  #include <linux/compiler.h>
>> > +#include <linux/fs.h>
>> > +#include <linux/shmem_fs.h>
>> >  #include <linux/types.h>
>> > 
>> >  static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
>> > @@ -31,19 +33,21 @@ static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
>> >  }
>> >  #define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
>> > 
>> > -static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
>> > +static inline unsigned long arch_calc_vm_flag_bits(struct file *file,
>> > +						   unsigned long flags)
>> >  {
>> >  	/*
>> >  	 * Only allow MTE on anonymous mappings as these are guaranteed to be
>> >  	 * backed by tags-capable memory. The vm_flags may be overridden by a
>> >  	 * filesystem supporting MTE (RAM-based).
>> 
>> We should also eventually remove the last sentence or even replace it with
>> its negation, or somebody might try reintroducing the pattern that won't
>> work anymore (wasn't there such a hugetlbfs thing in -next?).
> 
> I agree, we should update this comment as well though as a fix this
> patch is fine for now.
> 
> There is indeed a hugetlbfs change in -next adding VM_MTE_ALLOWED. It
> should still work after the above change but we'd need to move it over

I guess it will work after the above change, but not after 5/5?

> here (and fix the comment at the same time). We'll probably do it around
> -rc1 or maybe earlier once this fix hits mainline.

I assume this will hopefully go to rc7.

> I don't think we have
> an equivalent of shmem_file() for hugetlbfs, we'll need to figure
> something out.

I've found is_file_hugepages(), could work? And while adding the hugetlbfs
change here, the comment could be adjusted too, right?

> 
>> >  	 */
>> > -	if (system_supports_mte() && (flags & MAP_ANONYMOUS))
>> > +	if (system_supports_mte() &&
>> > +	    ((flags & MAP_ANONYMOUS) || shmem_file(file)))
>> >  		return VM_MTE_ALLOWED;
>> > 
>> >  	return 0;
>> >  }
> 
> This will conflict with the arm64 for-next/core tree as it's adding
> a MAP_HUGETLB check. Trivial resolution though, Stephen will handle it.
>