linux-kernel - [PATCH] riscv: hwprobe: export VA

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Message-ID: <20240201140319.360088-1-cleger@rivosinc.com>
Date: Thu,  1 Feb 2024 15:02:45 +0100
From: Clément Léger <cleger@...osinc.com>
To: Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	linux-doc@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: Clément Léger <cleger@...osinc.com>,
	Robin Ehn <rehn@...osinc.com>
Subject: [PATCH] riscv: hwprobe: export VA_BITS

Some userspace applications (OpenJDK for instance) uses the free bits
in pointers to insert additional information for their own logic.
Currently they rely on parsing /proc/cpuinfo to obtain the current value
of virtual address used bits [1]. Exporting VA_BITS through hwprobe will
allow for a more stable interface to be used.

Link: https://github.com/openjdk/jdk/blob/master/src/hotspot/os_cpu/linux_riscv/vm_version_linux_riscv.cpp#L171 [1]
Signed-off-by: Clément Léger <cleger@...osinc.com>

---
 Documentation/arch/riscv/hwprobe.rst  | 3 +++
 arch/riscv/include/asm/hwprobe.h      | 2 +-
 arch/riscv/include/uapi/asm/hwprobe.h | 1 +
 arch/riscv/kernel/sys_hwprobe.c       | 3 +++
 4 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
index b2bcc9eed9aa..6f198c6ed4f0 100644
--- a/Documentation/arch/riscv/hwprobe.rst
+++ b/Documentation/arch/riscv/hwprobe.rst
@@ -210,3 +210,6 @@ The following keys are defined:
 
 * :c:macro:`RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE`: An unsigned int which
   represents the size of the Zicboz block in bytes.
+
+* :c:macro:`RISCV_HWPROBE_KEY_VA_BITS`: An unsigned long which
+  represent the number of bits used to store virtual addresses.
diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
index 630507dff5ea..150a9877b0af 100644
--- a/arch/riscv/include/asm/hwprobe.h
+++ b/arch/riscv/include/asm/hwprobe.h
@@ -8,7 +8,7 @@
 
 #include <uapi/asm/hwprobe.h>
 
-#define RISCV_HWPROBE_MAX_KEY 6
+#define RISCV_HWPROBE_MAX_KEY 7
 
 static inline bool riscv_hwprobe_key_is_valid(__s64 key)
 {
diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
index 9f2a8e3ff204..2a5006cddb7b 100644
--- a/arch/riscv/include/uapi/asm/hwprobe.h
+++ b/arch/riscv/include/uapi/asm/hwprobe.h
@@ -67,6 +67,7 @@ struct riscv_hwprobe {
 #define		RISCV_HWPROBE_MISALIGNED_UNSUPPORTED	(4 << 0)
 #define		RISCV_HWPROBE_MISALIGNED_MASK		(7 << 0)
 #define RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE	6
+#define RISCV_HWPROBE_KEY_VA_BITS		7
 /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
 
 /* Flags */
diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
index a7c56b41efd2..328435836e36 100644
--- a/arch/riscv/kernel/sys_hwprobe.c
+++ b/arch/riscv/kernel/sys_hwprobe.c
@@ -202,6 +202,9 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
 		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOZ))
 			pair->value = riscv_cboz_block_size;
 		break;
+	case RISCV_HWPROBE_KEY_VA_BITS:
+		pair->value = VA_BITS;
+		break;
 
 	/*
 	 * For forward compatibility, unknown keys don't fail the whole
-- 
2.43.0