Messages in this thread | | | Date | Thu, 22 Aug 2013 07:56:26 +0100 | From | "Jan Beulich" <> | Subject | Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use |
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>>> On 21.08.13 at 18:19, Cyrill Gorcunov <gorcunov@gmail.com> wrote: > On Wed, Aug 21, 2013 at 05:03:13PM +0100, Jan Beulich wrote: >> > >> > Only to non-present ptes, as far as I know. >> >> That's not really any guarantee. And the accessor functions also >> don't check that they'd be used on non-present PTEs only. > > Wait. This _PAGE_SWP_SOFT_DIRTY bit (which is in real PSE bit) assigned > in only one place -- in try_to_unmap_one(). The PTE get non-present then > and consists of swap entry format. I don't see any accessor to such entry > without testing if it's swap entry or pte-none. What I'm missing?
Fact is that this
static inline pte_t pte_swp_mksoft_dirty(pte_t pte) { return pte_set_flags(pte, _PAGE_SWP_SOFT_DIRTY); }
has no checking whatsoever that the PTE being modified is a non-present one, not even in any of the debugging modes. It would be a different thing if the above acted on a swp_entry_t.
The fact that there currently may be just a single call site (where the caller guarantees the non-present state) is no guarantee that in the future another one won't appear, and then result in very hard to debug problems.
Jan
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