Re: [PATCH v5 11/39] x86/mm: Update pte_modify for _PAGE_COW

Edgecombe, Rick P
2023-02-17T16:53:49Z

On Fri, 2023-02-17 at 17:11 +0100, Borislav Petkov wrote:
> On Fri, Feb 10, 2023 at 05:00:05PM +0000, Edgecombe, Rick P wrote:
> > /*
> > * Dirty bit is not preserved above so it can be done
> > * in a special way for the shadow stack case, where it
> > * may need to set _PAGE_SAVED_DIRTY. __pte_mkdirty() will
> > do
> > * this in the case of shadow stack.
> > */
> > if (oldval & _PAGE_DIRTY)
> > if (cpu_feature_enabled(X86_FEATURE_USER_SHSTK) &&
> > !pte_write(pte_result))
> > pte_set_flags(pte_result,
> > _PAGE_SAVED_DIRTY);
> > else
> > pte_set_flags(pte_result, _PAGE_DIRTY);
> > }
> >
> > return pte_result;
> > }
> >
> > So the later logic of doing the _PAGE_SAVED_DIRTY (_PAGE_COW) part
> > is
> > not centralized. It's ok?
>
> I think so.
>
> 1. If you have a single pte_mkdirty() and not also a __ helper, then
> there's less confusion for callers as to which interface they
> should be
> using
>
> 2. The not centralized part is a single conditional so it's not like
> you're saving on gazillion code lines
>
> So I'd prefer that.
>
>
Fair enough, I'll adjust it. Thanks!