Re: [PATCH v3 5/9] mm/mprotect: add MM_CP_PERM_UPGRADE

["Carlos López" <clopez@suse.de>]

On 11/13/26 7:51 PM, David Hildenbrand (Arm) wrote:
>> diff --git a/mm/mprotect.c b/mm/mprotect.c
>> index 84bcfe0281d3..8c0fcd10f5a3 100644
>> --- a/mm/mprotect.c
>> +++ b/mm/mprotect.c
>> @@ -767,6 +767,17 @@ static const struct mm_walk_ops prot_none_walk_ops = {
>>  	.walk_lock		= PGWALK_WRLOCK,
>>  };
>>  
>> +static bool vma_flags_is_perm_upgrade(vma_flags_t old_vma_flags,
>> +				      vma_flags_t new_vma_flags)
> 
> Two tab indent.

Will fix

>> +{
>> +	vm_flags_t old = vma_flags_to_legacy(old_vma_flags);
>> +	vm_flags_t new = vma_flags_to_legacy(new_vma_flags);
>> +	/* VM_ACCOUNT does not affect page tables */
>> +	vm_flags_t mask = VM_READ | VM_WRITE | VM_EXEC | VM_ACCOUNT;
> 
> Why is VM_ACCOUNT a permission upgrade? At best it's "no change".
> 
> What am I missing?

It isn't, this just means to cover the case where mprotect(PROT_READ |
PROT_WRITE) on a private read-only VMA sets VM_ACCOUNT as well. Without
this, the change is not detected as an upgrade.

> Also, what you really care about is "no permission downgrade", and "no
> permission upgrade" is not the inverse of that ;)

Right, I'll rename it.