Hi Kirill,
On Thu, Jun 15, 2017 at 05:52:22PM +0300, Kirill A. Shutemov wrote:
> We need an atomic way to setup pmd page table entry, avoiding races with
> CPU setting dirty/accessed bits. This is required to implement
> pmdp_invalidate() that doesn't loose these bits.
>
> On PAE we have to use cmpxchg8b as we cannot assume what is value of new pmd
> and
> setting it up half-by-half can expose broken corrupted entry to CPU.
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: H. Peter Anvin <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
I'll look at this from the arm64 perspective. It would be good if we can
have a generic atomic implementation based on cmpxchg64 but I need to
look at the details first.
> +static inline pmd_t pmdp_establish(pmd_t *pmdp, pmd_t pmd)
> +{
> + pmd_t old;
> +
> + /*
> + * We cannot assume what is value of pmd here, so there's no easy way
> + * to set if half by half. We have to fall back to cmpxchg64.
> + */
> + {
BTW, you are missing a "do" here (and it probably compiles just fine
without it, though different behaviour).
> + old = *pmdp;
> + } while (cmpxchg64(&pmdp->pmd, old.pmd, pmd.pmd) != old.pmd);
> +
> + return old;
> +}
--
Catalin
