[RFC PATCH v2 16/20] powerpc/e500: Encode hugepage size in PTE bits

Christophe Leroy
2024-05-17T19:01:32Z

Use U0-U3 bits to encode hugepage size, more exactly page shift.

As we start using hugepages at shift 21 (2Mbytes), substract 20
so that it fits into 4 bits. That may change in the future if
we want to use smaller hugepages.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/include/asm/nohash/hugetlb-e500.h | 6 ++++++
arch/powerpc/include/asm/nohash/pte-e500.h | 3 +++
2 files changed, 9 insertions(+)

diff --git a/arch/powerpc/include/asm/nohash/hugetlb-e500.h b/arch/powerpc/include/asm/nohash/hugetlb-e500.h
index 8f04ad20e040..d8e51a3f8557 100644
--- a/arch/powerpc/include/asm/nohash/hugetlb-e500.h
+++ b/arch/powerpc/include/asm/nohash/hugetlb-e500.h
@@ -42,4 +42,10 @@ static inline int check_and_get_huge_psize(int shift)
return shift_to_mmu_psize(shift);
}

+static inline pte_t arch_make_huge_pte(pte_t entry, unsigned int shift, vm_flags_t flags)
+{
+ return __pte(pte_val(entry) | (_PAGE_U3 * (shift - 20)));
+}
+#define arch_make_huge_pte arch_make_huge_pte
+
#endif /* _ASM_POWERPC_NOHASH_HUGETLB_E500_H */
diff --git a/arch/powerpc/include/asm/nohash/pte-e500.h b/arch/powerpc/include/asm/nohash/pte-e500.h
index 975facc7e38e..091e4bff1fba 100644
--- a/arch/powerpc/include/asm/nohash/pte-e500.h
+++ b/arch/powerpc/include/asm/nohash/pte-e500.h
@@ -46,6 +46,9 @@
#define _PAGE_NO_CACHE 0x400000 /* I: cache inhibit */
#define _PAGE_WRITETHRU 0x800000 /* W: cache write-through */

+#define _PAGE_HSIZE_MSK (_PAGE_U0 | _PAGE_U1 | _PAGE_U2 | _PAGE_U3)
+#define _PAGE_HSIZE_SHIFT 14
+
/* "Higher level" linux bit combinations */
#define _PAGE_EXEC (_PAGE_BAP_SX | _PAGE_BAP_UX) /* .. and was cache cleaned */
#define _PAGE_READ (_PAGE_BAP_SR | _PAGE_BAP_UR) /* User read permission */
--
2.44.0