Re: [PATCH v7 22/41] mm/mmap: Add shadow stack pages to memory accounting

[Dave Hansen]

On 3/17/23 10:12, Deepak Gupta wrote:
>>  /*
>> - * Stack area - automatically grows in one direction
>> + * Stack area
>>   *
>> - * VM_GROWSUP / VM_GROWSDOWN VMAs are always private anonymous:
>> - * do_mmap() forbids all other combinations.
>> + * VM_GROWSUP, VM_GROWSDOWN VMAs are always private
>> + * anonymous. do_mmap() forbids all other combinations.
>>   */
>>  static inline bool is_stack_mapping(vm_flags_t flags)
>>  {
>> -       return (flags & VM_STACK) == VM_STACK;
>> +       return ((flags & VM_STACK) == VM_STACK) || (flags & VM_SHADOW_STACK);
> Same comment here. `VM_SHADOW_STACK` is an x86 specific way of
> encoding a shadow stack.
> Instead let's have a proxy here which allows architectures to have
> their own encodings to represent a shadow stack.

This doesn't _preclude_ another architecture from coming along and doing
that, right?  I'd just prefer that shadow stack architecture #2 comes
along and refactors this in precisely the way _they_ need it.