MIPS64: Support of at least 48 bits of SEGBITS
SEGBITS is 40 bits or more, depending on CPU type. Introduces optional
support for 48 bits of application virtual address space. Only 16K and
64K pages are supported.
Enabling will result in a memory overhead of a small number of pages for
small applications. For 64K pages a 3rd level of page tables is required
which has some impact during software TLB refill.
[ralf@linux-mips.org: Fixed things raised in the review of the version
posted and changed kconfig to be a bit more userfriendly.]
Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Cc: aleksey.makarov@auriga.com
Cc: james.hogan@imgtec.com
Cc: paul.burton@imgtec.com
Cc: david.daney@cavium.com
Cc: peterz@infradead.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: davidlohr@hp.com
Cc: kirill@shutemov.name
Cc: akpm@linux-foundation.org
Cc: mingo@kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/10051/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index d5c3621..2b7af90 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2076,6 +2076,16 @@
emulation when determining guest CPU Frequency. Instead, the guest's
timer frequency is specified directly.
+config MIPS_VA_BITS_48
+ bool "48 bits virtual memory"
+ depends on 64BIT
+ help
+ Support a maximum at least 48 bits of application virtual memory.
+ Default is 40 bits or less, depending on the CPU.
+ This option result in a small memory overhead for page tables.
+ This option is only supported with 16k and 64k page sizes.
+ If unsure, say N.
+
choice
prompt "Kernel page size"
default PAGE_SIZE_4KB
@@ -2083,6 +2093,7 @@
config PAGE_SIZE_4KB
bool "4kB"
depends on !CPU_LOONGSON2 && !CPU_LOONGSON3
+ depends on !MIPS_VA_BITS_48
help
This option select the standard 4kB Linux page size. On some
R3000-family processors this is the only available page size. Using
@@ -2092,6 +2103,7 @@
config PAGE_SIZE_8KB
bool "8kB"
depends on CPU_R8000 || CPU_CAVIUM_OCTEON
+ depends on !MIPS_VA_BITS_48
help
Using 8kB page size will result in higher performance kernel at
the price of higher memory consumption. This option is available
@@ -2110,6 +2122,7 @@
config PAGE_SIZE_32KB
bool "32kB"
depends on CPU_CAVIUM_OCTEON
+ depends on !MIPS_VA_BITS_48
help
Using 32kB page size will result in higher performance kernel at
the price of higher memory consumption. This option is available