powerpc/mm: Speed up computation of base and actual page size for a HPTE

This replaces a 2-D search through an array with a simple 8-bit table
lookup for determining the actual and/or base page size for a HPT entry.

The encoding in the second doubleword of the HPTE is designed to encode
the actual and base page sizes without using any more bits than would be
needed for a 4k page number, by using between 1 and 8 low-order bits of
the RPN (real page number) field to encode the page sizes.  A single
"large page" bit in the first doubleword indicates that these low-order
bits are to be interpreted like this.

We can determine the page sizes by using the low-order 8 bits of the RPN
to look up a 256-entry table.  For actual page sizes less than 1MB, some
of the upper bits of these 8 bits are going to be real address bits, but
we can cope with that by replicating the entries for those smaller page
sizes.

While we're at it, let's move the hpte_page_size() and hpte_base_page_size()
functions from a KVM-specific header to a header for 64-bit HPT systems,
since this computation doesn't have anything specifically to do with KVM.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

1 files changed, 2 insertions, 40 deletions

diff --git a/arch/powerpc/mm/hash_native_64.c b/arch/powerpc/mm/hash_native_64.c
index 0e4e9654bd2c..83ddc0e171b0 100644
--- a/arch/powerpc/mm/hash_native_64.c
+++ b/arch/powerpc/mm/hash_native_64.c
@@ -493,36 +493,6 @@ static void native_hugepage_invalidate(unsigned long vsid,
 }
 #endif
 
-static inline int __hpte_actual_psize(unsigned int lp, int psize)
-{
-	int i, shift;
-	unsigned int mask;
-
-	/* start from 1 ignoring MMU_PAGE_4K */
-	for (i = 1; i < MMU_PAGE_COUNT; i++) {
-
-		/* invalid penc */
-		if (mmu_psize_defs[psize].penc[i] == -1)
-			continue;
-		/*
-		 * encoding bits per actual page size
-		 *        PTE LP     actual page size
-		 *    rrrr rrrz		>=8KB
-		 *    rrrr rrzz		>=16KB
-		 *    rrrr rzzz		>=32KB
-		 *    rrrr zzzz		>=64KB
-		 * .......
-		 */
-		shift = mmu_psize_defs[i].shift - LP_SHIFT;
-		if (shift > LP_BITS)
-			shift = LP_BITS;
-		mask = (1 << shift) - 1;
-		if ((lp & mask) == mmu_psize_defs[psize].penc[i])
-			return i;
-	}
-	return -1;
-}
-
 static void hpte_decode(struct hash_pte *hpte, unsigned long slot,
 			int *psize, int *apsize, int *ssize, unsigned long *vpn)
 {
@@ -538,16 +508,8 @@ static void hpte_decode(struct hash_pte *hpte, unsigned long slot,
 		size   = MMU_PAGE_4K;
 		a_size = MMU_PAGE_4K;
 	} else {
-		for (size = 0; size < MMU_PAGE_COUNT; size++) {
-
-			/* valid entries have a shift value */
-			if (!mmu_psize_defs[size].shift)
-				continue;
-
-			a_size = __hpte_actual_psize(lp, size);
-			if (a_size != -1)
-				break;
-		}
+		size = hpte_page_sizes[lp] & 0xf;
+		a_size = hpte_page_sizes[lp] >> 4;
 	}
 	/* This works for all page sizes, and for 256M and 1T segments */
 	if (cpu_has_feature(CPU_FTR_ARCH_300))