Re: [PATCH RFC/RFT v2 1/2] mm: helper `is_shadow_stack_vma` to check shadow stack vma

[Deepak Gupta]

On Fri, Nov 01, 2024 at 09:47:25PM +0000, Edgecombe, Rick P wrote:
> On Wed, 2024-10-16 at 14:57 -0700, Deepak Gupta wrote:
> > VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) is used to encode shadow stack
> > VMA on three architectures (x86 shadow stack, arm GCS and RISC-V shadow
> > stack). In case architecture doesn't implement shadow stack, it's VM_NONE
> > Introducing a helper `is_shadow_stack_vma` to determine shadow stack vma
> > or not.
>
> I don't understand why we need this. IIRC was some discussion about wanting to
> abstract different ways of testing for shadow stack VMAs for different
> architectures since risc-v was going to do it differently. But now this says
> they are all the same, so what's wrong with the open coded check?

Yeah it was born out of the need due to risc-v overloading `VM_WRITE`. Given
that's out of the door, this helper is not useful for that need anymore.

However during rebasing I saw certain vma helpers were re-organized in a new
file `vma.h` and there was helper for stack as well. So I kept it. 

I don't know if it's helpful or harmful. Let me know, I can let it go as well.