[PATCH 1/7] powerpc: Free up four 64K PTE bits in 4K backed HPTE pages
Ram Pai
linuxram at us.ibm.com
Mon Jul 31 10:11:10 AEST 2017
Rearrange 64K PTE bits to free up bits 3, 4, 5 and 6,
in the 4K backed HPTE pages.These bits continue to be used
for 64K backed HPTE pages in this patch, but will be freed
up in the next patch. The bit numbers are big-endian as
defined in the ISA3.0
The patch does the following change to the 4k htpe backed
64K PTE's format.
H_PAGE_BUSY moves from bit 3 to bit 9 (B bit in the figure
below)
V0 which occupied bit 4 is not used anymore.
V1 which occupied bit 5 is not used anymore.
V2 which occupied bit 6 is not used anymore.
V3 which occupied bit 7 is not used anymore.
Before the patch, the 4k backed 64k PTE format was as follows
0 1 2 3 4 5 6 7 8 9 10...........................63
: : : : : : : : : : : :
v v v v v v v v v v v v
,-,-,-,-,--,--,--,--,-,-,-,-,-,------------------,-,-,-,
|x|x|x|B|V0|V1|V2|V3|x| | |x|x|................|x|x|x|x| <- primary pte
'_'_'_'_'__'__'__'__'_'_'_'_'_'________________'_'_'_'_'
|S|G|I|X|S |G |I |X |S|G|I|X|..................|S|G|I|X| <- secondary pte
'_'_'_'_'__'__'__'__'_'_'_'_'__________________'_'_'_'_'
After the patch, the 4k backed 64k PTE format is as follows
0 1 2 3 4 5 6 7 8 9 10...........................63
: : : : : : : : : : : :
v v v v v v v v v v v v
,-,-,-,-,--,--,--,--,-,-,-,-,-,------------------,-,-,-,
|x|x|x| | | | | |x|B| |x|x|................|.|.|.|.| <- primary pte
'_'_'_'_'__'__'__'__'_'_'_'_'_'________________'_'_'_'_'
|S|G|I|X|S |G |I |X |S|G|I|X|..................|S|G|I|X| <- secondary pte
'_'_'_'_'__'__'__'__'_'_'_'_'__________________'_'_'_'_'
the four bits S,G,I,X (one quadruplet per 4k HPTE) that
cache the hash-bucket slot value, is initialized to
1,1,1,1 indicating -- an invalid slot. If a HPTE gets
cached in a 1111 slot(i.e 7th slot of secondary hash
bucket), it is released immediately. In other words,
even though 1111 is a valid slot value in the hash
bucket, we consider it invalid and release the slot and
the HPTE. This gives us the opportunity to determine
the validity of S,G,I,X bits based on its contents and
not on any of the bits V0,V1,V2 or V3 in the primary PTE
When we release a HPTE cached in the 1111 slot
we also release a legitimate slot in the primary
hash bucket and unmap its corresponding HPTE. This
is to ensure that we do get a HPTE cached in a slot
of the primary hash bucket, the next time we retry.
Though treating 1111 slot as invalid, reduces the
number of available slots in the hash bucket and may
have an effect on the performance, the probabilty of
hitting a 1111 slot is extermely low.
Compared to the current scheme, the above described
scheme reduces the number of false hash table updates
significantly and has the added advantage of
releasing four valuable PTE bits for other purpose.
NOTE:even though bits 3, 4, 5, 6, 7 are not used when
the 64K PTE is backed by 4k HPTE, they continue to be
used if the PTE gets backed by 64k HPTE. The next
patch will decouple that aswell, and truely release the
bits.
This idea was jointly developed by Paul Mackerras,
Aneesh, Michael Ellermen and myself.
4K PTE format remains unchanged currently.
The patch does the following code changes
a) PTE flags are split between 64k and 4k header files.
b) __hash_page_4K() is reimplemented to reflect the
above logic.
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
Signed-off-by: Ram Pai <linuxram at us.ibm.com>
---
arch/powerpc/include/asm/book3s/64/hash-4k.h | 2 +
arch/powerpc/include/asm/book3s/64/hash-64k.h | 8 +--
arch/powerpc/include/asm/book3s/64/hash.h | 1 -
arch/powerpc/mm/hash64_64k.c | 74 ++++++++++++++++---------
arch/powerpc/mm/hash_utils_64.c | 4 +-
5 files changed, 55 insertions(+), 34 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/hash-4k.h b/arch/powerpc/include/asm/book3s/64/hash-4k.h
index 0c4e470..f959c00 100644
--- a/arch/powerpc/include/asm/book3s/64/hash-4k.h
+++ b/arch/powerpc/include/asm/book3s/64/hash-4k.h
@@ -16,6 +16,8 @@
#define H_PUD_TABLE_SIZE (sizeof(pud_t) << H_PUD_INDEX_SIZE)
#define H_PGD_TABLE_SIZE (sizeof(pgd_t) << H_PGD_INDEX_SIZE)
+#define H_PAGE_BUSY _RPAGE_RSV1 /* software: PTE & hash are busy */
+
/* PTE flags to conserve for HPTE identification */
#define _PAGE_HPTEFLAGS (H_PAGE_BUSY | H_PAGE_HASHPTE | \
H_PAGE_F_SECOND | H_PAGE_F_GIX)
diff --git a/arch/powerpc/include/asm/book3s/64/hash-64k.h b/arch/powerpc/include/asm/book3s/64/hash-64k.h
index 9732837..62e580c 100644
--- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
+++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h
@@ -12,18 +12,14 @@
*/
#define H_PAGE_COMBO _RPAGE_RPN0 /* this is a combo 4k page */
#define H_PAGE_4K_PFN _RPAGE_RPN1 /* PFN is for a single 4k page */
+#define H_PAGE_BUSY _RPAGE_RPN42 /* software: PTE & hash are busy */
+
/*
* We need to differentiate between explicit huge page and THP huge
* page, since THP huge page also need to track real subpage details
*/
#define H_PAGE_THP_HUGE H_PAGE_4K_PFN
-/*
- * Used to track subpage group valid if H_PAGE_COMBO is set
- * This overloads H_PAGE_F_GIX and H_PAGE_F_SECOND
- */
-#define H_PAGE_COMBO_VALID (H_PAGE_F_GIX | H_PAGE_F_SECOND)
-
/* PTE flags to conserve for HPTE identification */
#define _PAGE_HPTEFLAGS (H_PAGE_BUSY | H_PAGE_F_SECOND | \
H_PAGE_F_GIX | H_PAGE_HASHPTE | H_PAGE_COMBO)
diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
index 4e957b0..2d72964 100644
--- a/arch/powerpc/include/asm/book3s/64/hash.h
+++ b/arch/powerpc/include/asm/book3s/64/hash.h
@@ -9,7 +9,6 @@
*/
#define H_PTE_NONE_MASK _PAGE_HPTEFLAGS
#define H_PAGE_F_GIX_SHIFT 56
-#define H_PAGE_BUSY _RPAGE_RSV1 /* software: PTE & hash are busy */
#define H_PAGE_F_SECOND _RPAGE_RSV2 /* HPTE is in 2ndary HPTEG */
#define H_PAGE_F_GIX (_RPAGE_RSV3 | _RPAGE_RSV4 | _RPAGE_RPN44)
#define H_PAGE_HASHPTE _RPAGE_RPN43 /* PTE has associated HPTE */
diff --git a/arch/powerpc/mm/hash64_64k.c b/arch/powerpc/mm/hash64_64k.c
index 1a68cb1..7b92204 100644
--- a/arch/powerpc/mm/hash64_64k.c
+++ b/arch/powerpc/mm/hash64_64k.c
@@ -15,34 +15,22 @@
#include <linux/mm.h>
#include <asm/machdep.h>
#include <asm/mmu.h>
+
/*
- * index from 0 - 15
+ * return true, if the entry has a slot value which
+ * the software considers as invalid.
*/
-bool __rpte_sub_valid(real_pte_t rpte, unsigned long index)
+static inline bool hpte_soft_invalid(unsigned long slot)
{
- unsigned long g_idx;
- unsigned long ptev = pte_val(rpte.pte);
-
- g_idx = (ptev & H_PAGE_COMBO_VALID) >> H_PAGE_F_GIX_SHIFT;
- index = index >> 2;
- if (g_idx & (0x1 << index))
- return true;
- else
- return false;
+ return ((slot & 0xfUL) == 0xfUL);
}
+
/*
* index from 0 - 15
*/
-static unsigned long mark_subptegroup_valid(unsigned long ptev, unsigned long index)
+bool __rpte_sub_valid(real_pte_t rpte, unsigned long index)
{
- unsigned long g_idx;
-
- if (!(ptev & H_PAGE_COMBO))
- return ptev;
- index = index >> 2;
- g_idx = 0x1 << index;
-
- return ptev | (g_idx << H_PAGE_F_GIX_SHIFT);
+ return !(hpte_soft_invalid(rpte.hidx >> (index << 2)));
}
int __hash_page_4K(unsigned long ea, unsigned long access, unsigned long vsid,
@@ -50,12 +38,12 @@ int __hash_page_4K(unsigned long ea, unsigned long access, unsigned long vsid,
int ssize, int subpg_prot)
{
real_pte_t rpte;
- unsigned long *hidxp;
unsigned long hpte_group;
+ unsigned long *hidxp;
unsigned int subpg_index;
unsigned long rflags, pa, hidx;
unsigned long old_pte, new_pte, subpg_pte;
- unsigned long vpn, hash, slot;
+ unsigned long vpn, hash, slot, gslot;
unsigned long shift = mmu_psize_defs[MMU_PAGE_4K].shift;
/*
@@ -148,6 +136,15 @@ int __hash_page_4K(unsigned long ea, unsigned long access, unsigned long vsid,
}
htab_insert_hpte:
+
+ /*
+ * initialize all hidx entries to invalid value,
+ * the first time the PTE is about to allocate
+ * a 4K hpte
+ */
+ if (!(old_pte & H_PAGE_COMBO))
+ rpte.hidx = ~0x0UL;
+
/*
* handle H_PAGE_4K_PFN case
*/
@@ -172,15 +169,41 @@ int __hash_page_4K(unsigned long ea, unsigned long access, unsigned long vsid,
* Primary is full, try the secondary
*/
if (unlikely(slot == -1)) {
+ bool soft_invalid;
+
hpte_group = ((~hash & htab_hash_mask) * HPTES_PER_GROUP) & ~0x7UL;
slot = mmu_hash_ops.hpte_insert(hpte_group, vpn, pa,
rflags, HPTE_V_SECONDARY,
MMU_PAGE_4K, MMU_PAGE_4K,
ssize);
- if (slot == -1) {
- if (mftb() & 0x1)
+
+ soft_invalid = hpte_soft_invalid(slot);
+ if (unlikely(soft_invalid)) {
+ /*
+ * we got a valid slot from a hardware point of view.
+ * but we cannot use it, because we use this special
+ * value; as defined by hpte_soft_invalid(),
+ * to track invalid slots. We cannot use it.
+ * So invalidate it.
+ */
+ gslot = slot & _PTEIDX_GROUP_IX;
+ mmu_hash_ops.hpte_invalidate(hpte_group+gslot, vpn,
+ MMU_PAGE_4K, MMU_PAGE_4K,
+ ssize, 0);
+ }
+
+ if (unlikely(slot == -1 || soft_invalid)) {
+ /*
+ * for soft invalid slot, lets ensure that we
+ * release a slot from the primary, with the
+ * hope that we will acquire that slot next
+ * time we try. This will ensure that we do not
+ * get the same soft-invalid slot.
+ */
+ if (soft_invalid || (mftb() & 0x1))
hpte_group = ((hash & htab_hash_mask) *
HPTES_PER_GROUP) & ~0x7UL;
+
mmu_hash_ops.hpte_remove(hpte_group);
/*
* FIXME!! Should be try the group from which we removed ?
@@ -207,12 +230,11 @@ int __hash_page_4K(unsigned long ea, unsigned long access, unsigned long vsid,
hidxp = (unsigned long *)(ptep + PTRS_PER_PTE);
rpte.hidx &= ~(0xfUL << (subpg_index << 2));
*hidxp = rpte.hidx | (slot << (subpg_index << 2));
- new_pte = mark_subptegroup_valid(new_pte, subpg_index);
- new_pte |= H_PAGE_HASHPTE;
/*
* check __real_pte for details on matching smp_rmb()
*/
smp_wmb();
+ new_pte |= H_PAGE_HASHPTE;
*ptep = __pte(new_pte & ~H_PAGE_BUSY);
return 0;
}
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index f2095ce..1b494d0 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -975,8 +975,9 @@ void __init hash__early_init_devtree(void)
void __init hash__early_init_mmu(void)
{
+#ifndef CONFIG_PPC_64K_PAGES
/*
- * We have code in __hash_page_64K() and elsewhere, which assumes it can
+ * We have code in __hash_page_4K() and elsewhere, which assumes it can
* do the following:
* new_pte |= (slot << H_PAGE_F_GIX_SHIFT) & (H_PAGE_F_SECOND | H_PAGE_F_GIX);
*
@@ -987,6 +988,7 @@ void __init hash__early_init_mmu(void)
* with a BUILD_BUG_ON().
*/
BUILD_BUG_ON(H_PAGE_F_SECOND != (1ul << (H_PAGE_F_GIX_SHIFT + 3)));
+#endif /* CONFIG_PPC_64K_PAGES */
htab_init_page_sizes();
--
1.7.1
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