On Mon, Jun 26, 2017 at 09:03:18AM +1000, Balbir Singh wrote:

On Wed, 2017-06-21 at 18:39 -0700, Ram Pai wrote:

quoted

Introduce set_hidx_slot() which sets the (H_PAGE_F_SECOND|H_PAGE_F_GIX)
bits at  the  appropriate  location  in  the  PTE  of  4K  PTE.  In the
case of 64K PTE, it sets the bits in the second part of the PTE. Though
the implementation for the former just needs the slot parameter, it does
take some additional parameters to keep the prototype consistent.

This function will come in handy as we  work  towards  re-arranging the
bits in the later patches.

Signed-off-by: Ram Pai <redacted>
---
 arch/powerpc/include/asm/book3s/64/hash-4k.h  |  7 +++++++
 arch/powerpc/include/asm/book3s/64/hash-64k.h | 16 ++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/arch/powerpc/include/asm/book3s/64/hash-4k.h b/arch/powerpc/include/asm/book3s/64/hash-4k.h
index 9c2c8f1..cef644c 100644
--- a/arch/powerpc/include/asm/book3s/64/hash-4k.h
+++ b/arch/powerpc/include/asm/book3s/64/hash-4k.h

@@ -55,6 +55,13 @@ static inline int hash__hugepd_ok(hugepd_t hpd)
 }
 #endif
 
+static inline unsigned long set_hidx_slot(pte_t *ptep, real_pte_t rpte,
+			unsigned int subpg_index, unsigned long slot)
+{
+	return (slot << H_PAGE_F_GIX_SHIFT) &
+		(H_PAGE_F_SECOND | H_PAGE_F_GIX);
+}
+

A comment on top would help explain that 4k and 64k are different, 64k
is a new layout.

ok.

quoted

 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 
 static inline char *get_hpte_slot_array(pmd_t *pmdp)

diff --git a/arch/powerpc/include/asm/book3s/64/hash-64k.h b/arch/powerpc/include/asm/book3s/64/hash-64k.h
index 3f49941..4bac70a 100644
--- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
+++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h

@@ -75,6 +75,22 @@ static inline unsigned long __rpte_to_hidx(real_pte_t rpte, unsigned long index)
 	return (pte_val(rpte.pte) >> H_PAGE_F_GIX_SHIFT) & 0xf;
 }
 
+static inline unsigned long set_hidx_slot(pte_t *ptep, real_pte_t rpte,
+		unsigned int subpg_index, unsigned long slot)
+{
+	unsigned long *hidxp = (unsigned long *)(ptep + PTRS_PER_PTE);
+
+	rpte.hidx &= ~(0xfUL << (subpg_index << 2));
+	*hidxp = rpte.hidx  | (slot << (subpg_index << 2));
+	/*
+	 * Avoid race with __real_pte()
+	 * hidx must be committed to memory before committing
+	 * the pte.
+	 */
+	smp_wmb();

Whats the other paired barrier, is it in set_pte()?

 __real_pte() reads the hidx. The smp_rmb() is in that function.

quoted

+	return 0x0UL;
+}

We return 0 here and slot information for 4k pages, it is not that
clear

We return 0 here and commit the 4k-hpte hidx. 


RP