RE: [PATCH 20/35] mm: Update can_follow_write_pte() for shadow stack

David Laight
2022-02-10T22:47:05Z

From: Dave Hansen
> Sent: 09 February 2022 22:52
>
> On 1/30/22 13:18, Rick Edgecombe wrote:
> > Like a writable data page, a shadow stack page is writable, and becomes
> > read-only during copy-on-write, but it is always dirty.
>
> One other thing...
>
> The language in these changelogs is a bit sloppy. For instance, what
> does "always dirty" mean here? pte_dirty()? Or strictly _PAGE_DIRTY?
>
> In other words, logically dirty, or literally "has *the* dirty bit set"?

Doesn't COW have to set it readonly - so that the access faults.
And then set the fault code set it readonly+dirty (without write)
to allow the shadow stack accesses to not-fault.

Or am I mis-guessing what the docs actually say?

David

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