Hello, Nadav,
On Thu, Feb 17, 2022 at 09:16:02PM +0000, Nadav Amit wrote:
> From: Nadav Amit <namit@xxxxxxxxxx>
>
> When a PTE is set by UFFD operations such as UFFDIO_COPY, the PTE is
> currently only marked as write-protected if the VMA has VM_WRITE flag
> set. This seems incorrect or at least would be unexpected by the users.
>
> Consider the following sequence of operations that are being performed
> on a certain page:
>
> mprotect(PROT_READ)
> UFFDIO_COPY(UFFDIO_COPY_MODE_WP)
> mprotect(PROT_READ|PROT_WRITE)
No objection to the patch, however I'm wondering why this is a valid use
case because mprotect seems to be conflict with uffd, because AFAICT
mprotect(PROT_READ|PROT_WRITE) can already grant write bit.
In change_pte_range():
if (dirty_accountable && pte_dirty(ptent) &&
(pte_soft_dirty(ptent) ||
!(vma->vm_flags & VM_SOFTDIRTY))) {
ptent = pte_mkwrite(ptent);
}
PS: I always think here the VM_SOFTDIRTY check is wrong, IMHO it should be:
if (dirty_accountable && pte_dirty(ptent) &&
(pte_soft_dirty(ptent) ||
(vma->vm_flags & VM_SOFTDIRTY))) {
ptent = pte_mkwrite(ptent);
}
Because when VM_SOFTDIRTY is cleared it means soft dirty enabled. I wanted
to post a patch but I never yet.
Could I ask why you need mprotect() with uffd?
Thanks,
--
Peter Xu
