[PATCH 2/2] RISC-V: mm: Update documentation and include test

[Charlie Jenkins <charlie@rivosinc.com>]

Add documentation explaining the behavior of mmap. Include
a simple test that ensures that mmap returns an address less
than the hint address while there are still addresses available.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
---
 Documentation/riscv/vm-layout.rst             | 20 ++++++++
 arch/riscv/include/asm/pgtable.h              |  8 +--
 tools/testing/selftests/riscv/Makefile        |  2 +-
 tools/testing/selftests/riscv/mm/Makefile     | 22 +++++++++
 .../selftests/riscv/mm/testcases/mmap.c       | 49 +++++++++++++++++++
 5 files changed, 97 insertions(+), 4 deletions(-)
 create mode 100644 tools/testing/selftests/riscv/mm/Makefile
 create mode 100644 tools/testing/selftests/riscv/mm/testcases/mmap.c

diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-layout.rst
index 5462c84f4723..365a481be90b 100644
--- a/Documentation/riscv/vm-layout.rst
+++ b/Documentation/riscv/vm-layout.rst
@@ -133,3 +133,23 @@ RISC-V Linux Kernel SV57
    ffffffff00000000 |  -4     GB | ffffffff7fffffff |    2 GB | modules, BPF
    ffffffff80000000 |  -2     GB | ffffffffffffffff |    2 GB | kernel
   __________________|____________|__________________|_________|____________________________________________________________
+
+
+Userspace VAs
+--------------------
+To maintain compatibility with software that relies on the VA space
+with a maximum of 39-bits, the kernel will, by default, return virtual
+return virtual addresses to userspace from a 39-bit range.
+
+Software can "opt-in" to receiving VAs from other VA space by providing
+a hint address to mmap. A call to mmap is guaranteed to return an address
+that will not override the unset left-aligned bits in the hint address,
+unless there is no space left in the address space. If there is no space
+available in the requested address space, an address in the next smallest
+available address space will be returned.
+
+For example, in order to obtain 48-bit VA space, a hint address greater than
+:code:`1 << 38` must be provided. Note that this is 38 due to sv39 userspace
+ending at :code:`1 << 38` with the addresses beyond this and up to :code:`1 << 39`
+being reserved for the kernel. Similarly, to obtain 57-bit VA space addresses, a
+hint address greater than or equal to :code:`1 << 47` must be provided.
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index e83912e97870..93e7233d5d2a 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -841,14 +841,16 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
  * Task size is 0x4000000000 for RV64 or 0x9fc00000 for RV32.
  * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
  * Task size is:
- * -     0x9fc00000 (~2.5GB) for RV32.
- * -   0x4000000000 ( 256GB) for RV64 using SV39 mmu
- * - 0x800000000000 ( 128TB) for RV64 using SV48 mmu
+ * -        0x9fc00000	(~2.5GB) for RV32.
+ * -      0x4000000000	( 256GB) for RV64 using SV39 mmu
+ * -    0x800000000000	( 128TB) for RV64 using SV48 mmu
+ * - 0x100000000000000	(  64PB) for RV64 using SV57 mmu
  *
  * Note that PGDIR_SIZE must evenly divide TASK_SIZE since "RISC-V
  * Instruction Set Manual Volume II: Privileged Architecture" states that
  * "load and store effective addresses, which are 64bits, must have bits
  * 63–48 all equal to bit 47, or else a page-fault exception will occur."
+ * Similarly for SV57, bits 63–57 must be equal to bit 56.
  */
 #ifdef CONFIG_64BIT
 #define TASK_SIZE_64	(PGDIR_SIZE * PTRS_PER_PGD / 2)
diff --git a/tools/testing/selftests/riscv/Makefile b/tools/testing/selftests/riscv/Makefile
index 32a72902d045..0fee58f990ae 100644
--- a/tools/testing/selftests/riscv/Makefile
+++ b/tools/testing/selftests/riscv/Makefile
@@ -5,7 +5,7 @@
 ARCH ?= $(shell uname -m 2>/dev/null || echo not)
 
 ifneq (,$(filter $(ARCH),riscv))
-RISCV_SUBTARGETS ?= hwprobe
+RISCV_SUBTARGETS ?= hwprobe mm
 else
 RISCV_SUBTARGETS :=
 endif
diff --git a/tools/testing/selftests/riscv/mm/Makefile b/tools/testing/selftests/riscv/mm/Makefile
new file mode 100644
index 000000000000..4aadf04401db
--- /dev/null
+++ b/tools/testing/selftests/riscv/mm/Makefile
@@ -0,0 +1,22 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2019 ARM Limited
+# Originally tools/testing/selftests/arm64/signal
+
+# Additional include paths needed by kselftest.h and local headers
+CFLAGS += -D_GNU_SOURCE -std=gnu99 -I.
+
+SRCS := $(filter-out testcases/testcases.c,$(wildcard testcases/*.c))
+PROGS := $(patsubst %.c,%,$(SRCS))
+
+# Generated binaries to be installed by top KSFT script
+TEST_GEN_PROGS := $(notdir $(PROGS))
+
+# Get Kernel headers installed and use them.
+
+# Including KSFT lib.mk here will also mangle the TEST_GEN_PROGS list
+# to account for any OUTPUT target-dirs optionally provided by
+# the toplevel makefile
+include ../../lib.mk
+
+$(TEST_GEN_PROGS): $(PROGS)
+	cp $(PROGS) $(OUTPUT)/
\ No newline at end of file
diff --git a/tools/testing/selftests/riscv/mm/testcases/mmap.c b/tools/testing/selftests/riscv/mm/testcases/mmap.c
new file mode 100644
index 000000000000..aa37a623b93f
--- /dev/null
+++ b/tools/testing/selftests/riscv/mm/testcases/mmap.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <sys/mman.h>
+#include "../../kselftest_harness.h"
+
+TEST(sv57_test)
+{
+		// Only works on 64 bit
+		#if __riscv_xlen == 64
+		// Place all of the hint addresses on the boundaries of mmap
+		// sv39, sv48, sv57
+		// User addresses end at 1<<38, 1<<47, 1<<56 respectively
+		void *on_37_bits = (void *) (1UL << 37);
+		void *on_38_bits = (void *) (1UL << 38);
+		void *on_46_bits = (void *) (1UL << 46);
+		void *on_47_bits = (void *) (1UL << 47);
+		void *on_55_bits = (void *) (1UL << 55);
+		void *on_56_bits = (void *) (1UL << 56);
+
+		int prot = PROT_READ | PROT_WRITE;
+		int flags = MAP_PRIVATE | MAP_ANONYMOUS;
+
+		int *no_hint = mmap(NULL, 5*sizeof(int), prot, flags, 0, 0);
+		int *on_37_addr = mmap(on_37_bits, 5*sizeof(int), prot, flags, 0, 0);
+		int *on_38_addr = mmap(on_38_bits, 5*sizeof(int), prot, flags, 0, 0);
+		int *on_46_addr = mmap(on_46_bits, 5*sizeof(int), prot, flags, 0, 0);
+		int *on_47_addr = mmap(on_47_bits, 5*sizeof(int), prot, flags, 0, 0);
+		int *on_55_addr = mmap(on_55_bits, 5*sizeof(int), prot, flags, 0, 0);
+		int *on_56_addr = mmap(on_56_bits, 5*sizeof(int), prot, flags, 0, 0);
+
+		EXPECT_NE(no_hint, MAP_FAILED);
+		EXPECT_NE(on_37_addr, MAP_FAILED);
+		EXPECT_NE(on_38_addr, MAP_FAILED);
+		EXPECT_NE(on_46_addr, MAP_FAILED);
+		EXPECT_NE(on_47_addr, MAP_FAILED);
+		EXPECT_NE(on_55_addr, MAP_FAILED);
+		EXPECT_NE(on_56_addr, MAP_FAILED);
+
+		EXPECT_LT((unsigned long) no_hint, 1UL << 38);
+		EXPECT_LT((unsigned long) on_37_addr, 1UL << 38);
+		EXPECT_LT((unsigned long) on_38_addr, 1UL << 38);
+		EXPECT_LT((unsigned long) on_46_addr, 1UL << 38);
+		EXPECT_LT((unsigned long) on_47_addr, 1UL << 47);
+		EXPECT_LT((unsigned long) on_55_addr, 1UL << 47);
+		EXPECT_LT((unsigned long) on_56_addr, 1UL << 57);
+		#else
+		#endif
+}
+
+TEST_HARNESS_MAIN
-- 
2.34.1