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

[Yang Shi <yang@os.amperecomputing.com>]

On 10/30/24 4:53 AM, Lorenzo Stoakes wrote:
> On Wed, Oct 30, 2024 at 12:09:43PM +0100, Vlastimil Babka wrote:
>> 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.
> To be clear - this is a CRITICAL fix that MUST land for 6.12. I'd be inclined to
> try to get it to an earlier rc-.
>
>>> 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?
> Right but the MAP_HUGETLB should work to? Can we save such changes that
> alter any kind of existing behaviour to later series?

We should need both because mmap hugetlbfs file may not use MAP_HUGETLB.

>
> As this is going to be backported (by me...!) and I don't want to risk
> inadvertant changes.
>
>>>>>   	 */
>>>>> -	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.
> Thanks!
>