On Oct 3, 2022, at 3:28 PM, Edgecombe, Rick P [off-list ref] wrote:

On Mon, 2022-10-03 at 11:11 -0700, Nadav Amit wrote:

quoted

Did you have a look at ptep_set_access_flags() and friends and
checked they
do not need to be changed too? 

ptep_set_access_flags() doesn't actually set any additional dirty bits
on x86, so I think it's ok.

Are you sure about that? (lost my confidence today so I am hesitant).

Looking on insert_pfn(), I see:

                        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                        if (ptep_set_access_flags(vma, addr, pte, entry, 1)) ...

This appears to set the dirty bit while potentially leaving the write-bit
clear. This is the scenario you want to avoid, no?

quoted

Perhaps you should at least add some
assertion just to ensure nothing breaks.

You mean in ptep_set_access_flags()? I think some assertions would be
really great, I'm just not sure where.

Yes, on x86’s version of the function.