[10/13] x86/mm/pae: Be consistent with pXXp_get_and_clear()
Commit Message
Given that ptep_get_and_clear() uses cmpxchg8b, and that should be by
far the most common case, there's no point in having an optimized
variant for pmd/pud.
Introduce the pxx_xchg64() helper to implement the common logic once.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/pgtable-3level.h | 67 ++++++++--------------------------
1 file changed, 17 insertions(+), 50 deletions(-)
Comments
On Sat, Oct 22, 2022 at 4:48 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> +
> +#define pxx_xchg64(_pxx, _ptr, _val) ({ \
> + _pxx##val_t *_p = (_pxx##val_t *)_ptr; \
> + _pxx##val_t _o = *_p; \
> + do { } while (!try_cmpxchg64(_p, &_o, (_val))); \
> + native_make_##_pxx(_o); \
> +})
I think this could just be a "xchp64()", but if the pte/pmd code is
the only thing that actually wants this on 32-bit architectures, I'm
certainly ok with making it be specific to just this code, and calling
it "pxx_xchg()".
I wonder if there's some driver somewhere that wanted to use it, but
just made it be
depends on CONFIG_64BIT
instead, or made it use a cmpxchg64() loop because a plain xchg() didn't work.
I guess it really doesn't matter, with 32-bit being relegated to
legacy status anyway. No need to try to expand usage.
Linus
On Sat, Oct 22, 2022 at 10:53:42AM -0700, Linus Torvalds wrote:
> On Sat, Oct 22, 2022 at 4:48 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > +
> > +#define pxx_xchg64(_pxx, _ptr, _val) ({ \
> > + _pxx##val_t *_p = (_pxx##val_t *)_ptr; \
> > + _pxx##val_t _o = *_p; \
> > + do { } while (!try_cmpxchg64(_p, &_o, (_val))); \
> > + native_make_##_pxx(_o); \
> > +})
>
> I think this could just be a "xchp64()", but if the pte/pmd code is
> the only thing that actually wants this on 32-bit architectures, I'm
> certainly ok with making it be specific to just this code, and calling
> it "pxx_xchg()".
Regular xchg64() didn't work, the casting crud there is required because
of how pxx_t is a struct.
Now I could obviously do a xchg64(), but then we'd still need this
wrapper -- and yeah, I don't know how many other users there are.
@@ -90,34 +90,33 @@ static inline void pud_clear(pud_t *pudp
*/
}
+
+#define pxx_xchg64(_pxx, _ptr, _val) ({ \
+ _pxx##val_t *_p = (_pxx##val_t *)_ptr; \
+ _pxx##val_t _o = *_p; \
+ do { } while (!try_cmpxchg64(_p, &_o, (_val))); \
+ native_make_##_pxx(_o); \
+})
+
#ifdef CONFIG_SMP
static inline pte_t native_ptep_get_and_clear(pte_t *ptep)
{
- pte_t old = *ptep;
-
- do {
- } while (!try_cmpxchg64(&ptep->pte, &old.pte, 0ULL));
-
- return old;
+ return pxx_xchg64(pte, ptep, 0ULL);
}
-#else
-#define native_ptep_get_and_clear(xp) native_local_ptep_get_and_clear(xp)
-#endif
-#ifdef CONFIG_SMP
static inline pmd_t native_pmdp_get_and_clear(pmd_t *pmdp)
{
- pmd_t res;
-
- /* xchg acts as a barrier before setting of the high bits */
- res.pmd_low = xchg(&pmdp->pmd_low, 0);
- res.pmd_high = READ_ONCE(pmdp->pmd_high);
- WRITE_ONCE(pmdp->pmd_high, 0);
+ return pxx_xchg64(pmd, pmdp, 0ULL);
+}
- return res;
+static inline pud_t native_pudp_get_and_clear(pud_t *pudp)
+{
+ return pxx_xchg64(pud, pudp, 0ULL);
}
#else
+#define native_ptep_get_and_clear(xp) native_local_ptep_get_and_clear(xp)
#define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp)
+#define native_pudp_get_and_clear(xp) native_local_pudp_get_and_clear(xp)
#endif
#ifndef pmdp_establish
@@ -141,40 +140,8 @@ static inline pmd_t pmdp_establish(struc
return old;
}
- do {
- old = *pmdp;
- } while (cmpxchg64(&pmdp->pmd, old.pmd, pmd.pmd) != old.pmd);
-
- return old;
-}
-#endif
-
-#ifdef CONFIG_SMP
-union split_pud {
- struct {
- u32 pud_low;
- u32 pud_high;
- };
- pud_t pud;
-};
-
-static inline pud_t native_pudp_get_and_clear(pud_t *pudp)
-{
- union split_pud res, *orig = (union split_pud *)pudp;
-
-#ifdef CONFIG_PAGE_TABLE_ISOLATION
- pti_set_user_pgtbl(&pudp->p4d.pgd, __pgd(0));
-#endif
-
- /* xchg acts as a barrier before setting of the high bits */
- res.pud_low = xchg(&orig->pud_low, 0);
- res.pud_high = orig->pud_high;
- orig->pud_high = 0;
-
- return res.pud;
+ return pxx_xchg64(pmd, pmdp, pmd.pmd);
}
-#else
-#define native_pudp_get_and_clear(xp) native_local_pudp_get_and_clear(xp)
#endif
/* Encode and de-code a swap entry */