Merge patch series "riscv: mm: Extend mappable memory up to hint address"

Charlie Jenkins <charlie@rivosinc.com> says:

On riscv, mmap currently returns an address from the largest address
space that can fit entirely inside of the hint address. This makes it
such that the hint address is almost never returned. This patch raises
the mappable area up to and including the hint address. This allows mmap
to often return the hint address, which allows a performance improvement
over searching for a valid address as well as making the behavior more
similar to other architectures.

Note that a previous patch introduced stronger semantics compared to
other architectures for riscv mmap. On riscv, mmap will not use bits in
the upper bits of the virtual address depending on the hint address. On
other architectures, a random address is returned in the address space
requested. On all architectures the hint address will be returned if it
is available. This allows riscv applications to configure how many bits
in the virtual address should be left empty. This has the two benefits
of being able to request address spaces that are smaller than the
default and doesn't require the application to know the page table
layout of riscv.

* b4-shazam-merge:
  docs: riscv: Define behavior of mmap
  selftests: riscv: Generalize mm selftests
  riscv: mm: Use hint address in mmap if available

Link: https://lore.kernel.org/r/20240130-use_mmap_hint_address-v3-0-8a655cfa8bcb@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm/compat.h
index 2ac955b51148f4..aa103530a5c83a 100644
--- a/arch/riscv/include/asm/compat.h
+++ b/arch/riscv/include/asm/compat.h
@@ -14,9 +14,28 @@
 
 static inline int is_compat_task(void)
 {
+	if (!IS_ENABLED(CONFIG_COMPAT))
+		return 0;
+
 	return test_thread_flag(TIF_32BIT);
 }
 
+static inline int is_compat_thread(struct thread_info *thread)
+{
+	if (!IS_ENABLED(CONFIG_COMPAT))
+		return 0;
+
+	return test_ti_thread_flag(thread, TIF_32BIT);
+}
+
+static inline void set_compat_task(bool is_compat)
+{
+	if (is_compat)
+		set_thread_flag(TIF_32BIT);
+	else
+		clear_thread_flag(TIF_32BIT);
+}
+
 struct compat_user_regs_struct {
 	compat_ulong_t pc;
 	compat_ulong_t ra;