[PATCH v4 0/6] RISC-V Hardware Probing User Interface

[PATCH v4 0/6] RISC-V Hardware Probing User Interface

[Evan Green]

There's been a bunch of off-list discussions about this, including at
Plumbers.  The original plan was to do something involving providing an
ISA string to userspace, but ISA strings just aren't sufficient for a
stable ABI any more: in order to parse an ISA string users need the
version of the specifications that the string is written to, the version
of each extension (sometimes at a finer granularity than the RISC-V
releases/versions encode), and the expected use case for the ISA string
(ie, is it a U-mode or M-mode string).  That's a lot of complexity to
try and keep ABI compatible and it's probably going to continue to grow,
as even if there's no more complexity in the specifications we'll have
to deal with the various ISA string parsing oddities that end up all
over userspace.

Instead this patch set takes a very different approach and provides a set
of key/value pairs that encode various bits about the system.  The big
advantage here is that we can clearly define what these mean so we can
ensure ABI stability, but it also allows us to encode information that's
unlikely to ever appear in an ISA string (see the misaligned access
performance, for example).  The resulting interface looks a lot like
what arm64 and x86 do, and will hopefully fit well into something like
ACPI in the future.

The actual user interface is a syscall, with a vDSO function in front of
it. The vDSO function can answer some queries without a syscall at all,
and falls back to the syscall for cases it doesn't have answers to.
Currently we prepopulate it with an array of answers for all keys and
a CPU set of "all CPUs". This can be adjusted as necessary to provide
fast answers to the most common queries.

An example series in glibc exposing this syscall and using it in an
ifunc selector for memcpy can be found at [1]. I'm about to send a v2
of that series out that incorporates the vDSO function.

I was asked about the performance delta between this and something like
sysfs. I created a small test program [2] and ran it on a Nezha D1
Allwinner board. Doing each operation 100000 times and dividing, these
operations take the following amount of time:
 - open()+read()+close() of /sys/kernel/cpu_byteorder: 3.8us
 - access("/sys/kernel/cpu_byteorder", R_OK): 1.3us
 - riscv_hwprobe() vDSO and syscall: .0094us
 - riscv_hwprobe() vDSO with no syscall: 0.0091us

These numbers get farther apart if we query multiple keys, as sysfs will
scale linearly with the number of keys, where the dedicated syscall
stays the same. To frame these numbers, I also did a tight
fork/exec/wait loop, which I measured as 4.8ms. So doing 4
open/read/close operations is a delta of about 0.3%, versus a single vDSO
call is a delta of essentially zero.

[1] https://public-inbox.org/libc-alpha/20230206194819.1679472-1-evan@rivosinc.com/T/#t
[2] https://pastebin.com/x84NEKaS

Changes in v4:
 - Used real types in syscall prototypes (Arnd)
 - Fixed static line break in do_riscv_hwprobe() (Conor)
 - Added newlines between documentation lists (Conor)
 - Crispen up size types to size_t, and cpu indices to int (Joe)
 - Fix copy_from_user() return logic bug (found via kselftests!)
 - Add __user to SYSCALL_DEFINE() to fix warning
 - More newlines in BASE_BEHAVIOR_IMA documentation (Conor)
 - Add newlines to CPUPERF_0 documentation (Conor)
 - Add UNSUPPORTED value (Conor)
 - Switched from DT to alternatives-based probing (Rob)
 - Crispen up cpu index type to always be int (Conor)
 - Fixed selftests commit description, no more tiny libc (Mark Brown)
 - Fixed selftest syscall prototype types to match v4.
 - Added a prototype to fix -Wmissing-prototype warning (lkp@intel.com)
 - Fixed rv32 build failure (lkp@intel.com)
 - Make vdso prototype match syscall types update

Changes in v3:
 - Updated copyright date in cpufeature.h
 - Fixed typo in cpufeature.h comment (Conor)
 - Refactored functions so that kernel mode can query too, in
   preparation for the vDSO data population.
 - Changed the vendor/arch/imp IDs to return a value of -1 on mismatch
   rather than failing the whole call.
 - Const cpumask pointer in hwprobe_mid()
 - Embellished documentation WRT cpu_set and the returned values.
 - Renamed hwprobe_mid() to hwprobe_arch_id() (Conor)
 - Fixed machine ID doc warnings, changed elements to c:macro:.
 - Completed dangling unistd.h comment (Conor)
 - Fixed line breaks and minor logic optimization (Conor).
 - Use riscv_cached_mxxxid() (Conor)
 - Refactored base ISA behavior probe to allow kernel probing as well,
   in prep for vDSO data initialization.
 - Fixed doc warnings in IMA text list, use :c:macro:.
 - Have hwprobe_misaligned return int instead of long.
 - Constify cpumask pointer in hwprobe_misaligned()
 - Fix warnings in _PERF_O list documentation, use :c:macro:.
 - Move include cpufeature.h to misaligned patch.
 - Fix documentation mismatch for RISCV_HWPROBE_KEY_CPUPERF_0 (Conor)
 - Use for_each_possible_cpu() instead of NR_CPUS (Conor)
 - Break early in misaligned access iteration (Conor)
 - Increase MISALIGNED_MASK from 2 bits to 3 for possible UNSUPPORTED future
   value (Conor)
 - Introduced vDSO function

Changes in v2:
 - Factored the move of struct riscv_cpuinfo to its own header
 - Changed the interface to look more like poll(). Rather than supplying
   key_offset and getting back an array of values with numerically
   contiguous keys, have the user pre-fill the key members of the array,
   and the kernel will fill in the corresponding values. For any key it
   doesn't recognize, it will set the key of that element to -1. This
   allows usermode to quickly ask for exactly the elements it cares
   about, and not get bogged down in a back and forth about newer keys
   that older kernels might not recognize. In other words, the kernel
   can communicate that it doesn't recognize some of the keys while
   still providing the data for the keys it does know.
 - Added a shortcut to the cpuset parameters that if a size of 0 and
   NULL is provided for the CPU set, the kernel will use a cpu mask of
   all online CPUs. This is convenient because I suspect most callers
   will only want to act on a feature if it's supported on all CPUs, and
   it's a headache to dynamically allocate an array of all 1s, not to
   mention a waste to have the kernel loop over all of the offline bits.
 - Fixed logic error in if(of_property_read_string...) that caused crash
 - Include cpufeature.h in cpufeature.h to avoid undeclared variable
   warning.
 - Added a _MASK define
 - Fix random checkpatch complaints
 - Updated the selftests to the new API and added some more.
 - Fixed indentation, comments in .S, and general checkpatch complaints.

Evan Green (6):
  RISC-V: Move struct riscv_cpuinfo to new header
  RISC-V: Add a syscall for HW probing
  RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA
  RISC-V: hwprobe: Support probing of misaligned access performance
  selftests: Test the new RISC-V hwprobe interface
  RISC-V: Add hwprobe vDSO function and data

 Documentation/riscv/hwprobe.rst               |  86 +++++++
 Documentation/riscv/index.rst                 |   1 +
 arch/riscv/Kconfig                            |   1 +
 arch/riscv/errata/thead/errata.c              |   9 +
 arch/riscv/include/asm/alternative.h          |   5 +
 arch/riscv/include/asm/cpufeature.h           |  23 ++
 arch/riscv/include/asm/hwprobe.h              |  13 +
 arch/riscv/include/asm/syscall.h              |   4 +
 arch/riscv/include/asm/vdso/data.h            |  17 ++
 arch/riscv/include/asm/vdso/gettimeofday.h    |   8 +
 arch/riscv/include/uapi/asm/hwprobe.h         |  37 +++
 arch/riscv/include/uapi/asm/unistd.h          |   9 +
 arch/riscv/kernel/alternative.c               |  19 ++
 arch/riscv/kernel/cpu.c                       |   8 +-
 arch/riscv/kernel/cpufeature.c                |   3 +
 arch/riscv/kernel/smpboot.c                   |   1 +
 arch/riscv/kernel/sys_riscv.c                 | 225 +++++++++++++++++-
 arch/riscv/kernel/vdso.c                      |   6 -
 arch/riscv/kernel/vdso/Makefile               |   2 +
 arch/riscv/kernel/vdso/hwprobe.c              |  52 ++++
 arch/riscv/kernel/vdso/sys_hwprobe.S          |  15 ++
 arch/riscv/kernel/vdso/vdso.lds.S             |   1 +
 tools/testing/selftests/Makefile              |   1 +
 tools/testing/selftests/riscv/Makefile        |  58 +++++
 .../testing/selftests/riscv/hwprobe/Makefile  |  10 +
 .../testing/selftests/riscv/hwprobe/hwprobe.c |  90 +++++++
 .../selftests/riscv/hwprobe/sys_hwprobe.S     |  12 +
 27 files changed, 703 insertions(+), 13 deletions(-)
 create mode 100644 Documentation/riscv/hwprobe.rst
 create mode 100644 arch/riscv/include/asm/cpufeature.h
 create mode 100644 arch/riscv/include/asm/hwprobe.h
 create mode 100644 arch/riscv/include/asm/vdso/data.h
 create mode 100644 arch/riscv/include/uapi/asm/hwprobe.h
 create mode 100644 arch/riscv/kernel/vdso/hwprobe.c
 create mode 100644 arch/riscv/kernel/vdso/sys_hwprobe.S
 create mode 100644 tools/testing/selftests/riscv/Makefile
 create mode 100644 tools/testing/selftests/riscv/hwprobe/Makefile
 create mode 100644 tools/testing/selftests/riscv/hwprobe/hwprobe.c
 create mode 100644 tools/testing/selftests/riscv/hwprobe/sys_hwprobe.S

-- 
2.25.1

[PATCH v4 2/6] RISC-V: Add a syscall for HW probing

[Evan Green]

We don't have enough space for these all in ELF_HWCAP{,2} and there's no
system call that quite does this, so let's just provide an arch-specific
one to probe for hardware capabilities.  This currently just provides
m{arch,imp,vendor}id, but with the key-value pairs we can pass more in
the future.

Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Evan Green <evan@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

---

Changes in v4:
 - Used real types in syscall prototypes (Arnd)
 - Fixed static line break in do_riscv_hwprobe() (Conor)
 - Added newlines between documentation lists (Conor)
 - Crispen up size types to size_t, and cpu indices to int (Joe)
 - Fix copy_from_user() return logic bug (found via kselftests!)
 - Add __user to SYSCALL_DEFINE() to fix warning

Changes in v3:
 - Refactored functions so that kernel mode can query too, in
   preparation for the vDSO data population.
 - Changed the vendor/arch/imp IDs to return a value of -1 on mismatch
   rather than failing the whole call.
 - Const cpumask pointer in hwprobe_mid()
 - Embellished documentation WRT cpu_set and the returned values.
 - Renamed hwprobe_mid() to hwprobe_arch_id() (Conor)
 - Fixed machine ID doc warnings, changed elements to c:macro:.
 - Completed dangling unistd.h comment (Conor)
 - Fixed line breaks and minor logic optimization (Conor).
 - Use riscv_cached_mxxxid() (Conor)

Changes in v2:
 - Changed the interface to look more like poll(). Rather than supplying
   key_offset and getting back an array of values with numerically
   contiguous keys, have the user pre-fill the key members of the array,
   and the kernel will fill in the corresponding values. For any key it
   doesn't recognize, it will set the key of that element to -1. This
   allows usermode to quickly ask for exactly the elements it cares
   about, and not get bogged down in a back and forth about newer keys
   that older kernels might not recognize. In other words, the kernel
   can communicate that it doesn't recognize some of the keys while
   still providing the data for the keys it does know.
 - Added a shortcut to the cpuset parameters that if a size of 0 and
   NULL is provided for the CPU set, the kernel will use a cpu mask of
   all online CPUs. This is convenient because I suspect most callers
   will only want to act on a feature if it's supported on all CPUs, and
   it's a headache to dynamically allocate an array of all 1s, not to
   mention a waste to have the kernel loop over all of the offline bits.


---
 Documentation/riscv/hwprobe.rst       |  41 ++++++++
 Documentation/riscv/index.rst         |   1 +
 arch/riscv/include/asm/hwprobe.h      |  13 +++
 arch/riscv/include/asm/syscall.h      |   4 +
 arch/riscv/include/uapi/asm/hwprobe.h |  25 +++++
 arch/riscv/include/uapi/asm/unistd.h  |   9 ++
 arch/riscv/kernel/sys_riscv.c         | 136 +++++++++++++++++++++++++-
 7 files changed, 228 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/riscv/hwprobe.rst
 create mode 100644 arch/riscv/include/asm/hwprobe.h
 create mode 100644 arch/riscv/include/uapi/asm/hwprobe.h

diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
new file mode 100644
index 000000000000..211828f706e3
--- /dev/null
+++ b/Documentation/riscv/hwprobe.rst
@@ -0,0 +1,41 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+RISC-V Hardware Probing Interface
+---------------------------------
+
+The RISC-V hardware probing interface is based around a single syscall, which
+is defined in <asm/hwprobe.h>::
+
+    struct riscv_hwprobe {
+        __s64 key;
+        __u64 value;
+    };
+
+    long sys_riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count,
+                           size_t cpu_count, cpu_set_t *cpus,
+                           unsigned int flags);
+
+The arguments are split into three groups: an array of key-value pairs, a CPU
+set, and some flags. The key-value pairs are supplied with a count. Userspace
+must prepopulate the key field for each element, and the kernel will fill in the
+value if the key is recognized. If a key is unknown to the kernel, its key field
+will be cleared to -1, and its value set to 0. The CPU set is defined by
+CPU_SET(3). For value-like keys (eg. vendor/arch/impl), the returned value will
+be only be valid if all CPUs in the given set have the same value. Otherwise -1
+will be returned. For boolean-like keys, the value returned will be a logical
+AND of the values for the specified CPUs. Usermode can supply NULL for cpus and
+0 for cpu_count as a shortcut for all online CPUs. There are currently no flags,
+this value must be zero for future compatibility.
+
+On success 0 is returned, on failure a negative error code is returned.
+
+The following keys are defined:
+
+* :c:macro:`RISCV_HWPROBE_KEY_MVENDORID`: Contains the value of ``mvendorid``,
+  as defined by the RISC-V privileged architecture specification.
+
+* :c:macro:`RISCV_HWPROBE_KEY_MARCHID`: Contains the value of ``marchid``, as
+  defined by the RISC-V privileged architecture specification.
+
+* :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as
+  defined by the RISC-V privileged architecture specification.
diff --git a/Documentation/riscv/index.rst b/Documentation/riscv/index.rst
index 2e5b18fbb145..175a91db0200 100644
--- a/Documentation/riscv/index.rst
+++ b/Documentation/riscv/index.rst
@@ -7,6 +7,7 @@ RISC-V architecture
 
     boot-image-header
     vm-layout
+    hwprobe
     patch-acceptance
     uabi
 
diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
new file mode 100644
index 000000000000..08d1c3bdd78a
--- /dev/null
+++ b/arch/riscv/include/asm/hwprobe.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright 2022 Rivos, Inc
+ */
+
+#ifndef _ASM_HWPROBE_H
+#define _ASM_HWPROBE_H
+
+#include <uapi/asm/hwprobe.h>
+
+#define RISCV_HWPROBE_MAX_KEY 2
+
+#endif
diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index 384a63b86420..3b5a667928bf 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -10,6 +10,7 @@
 #ifndef _ASM_RISCV_SYSCALL_H
 #define _ASM_RISCV_SYSCALL_H
 
+#include <asm/hwprobe.h>
 #include <uapi/linux/audit.h>
 #include <linux/sched.h>
 #include <linux/err.h>
@@ -75,4 +76,7 @@ static inline int syscall_get_arch(struct task_struct *task)
 }
 
 asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t);
+
+asmlinkage long sys_riscv_hwprobe(struct riscv_hwprobe *, size_t, size_t,
+				  unsigned long *, unsigned int);
 #endif	/* _ASM_RISCV_SYSCALL_H */
diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
new file mode 100644
index 000000000000..591802047460
--- /dev/null
+++ b/arch/riscv/include/uapi/asm/hwprobe.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright 2022 Rivos, Inc
+ */
+
+#ifndef _UAPI_ASM_HWPROBE_H
+#define _UAPI_ASM_HWPROBE_H
+
+#include <linux/types.h>
+
+/*
+ * Interface for probing hardware capabilities from userspace, see
+ * Documentation/riscv/hwprobe.rst for more information.
+ */
+struct riscv_hwprobe {
+	__s64 key;
+	__u64 value;
+};
+
+#define RISCV_HWPROBE_KEY_MVENDORID	0
+#define RISCV_HWPROBE_KEY_MARCHID	1
+#define RISCV_HWPROBE_KEY_MIMPID	2
+/* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
+
+#endif
diff --git a/arch/riscv/include/uapi/asm/unistd.h b/arch/riscv/include/uapi/asm/unistd.h
index 73d7cdd2ec49..950ab3fd4409 100644
--- a/arch/riscv/include/uapi/asm/unistd.h
+++ b/arch/riscv/include/uapi/asm/unistd.h
@@ -43,3 +43,12 @@
 #define __NR_riscv_flush_icache (__NR_arch_specific_syscall + 15)
 #endif
 __SYSCALL(__NR_riscv_flush_icache, sys_riscv_flush_icache)
+
+/*
+ * Allows userspace to query the kernel for CPU architecture and
+ * microarchitecture details across a given set of CPUs.
+ */
+#ifndef __NR_riscv_hwprobe
+#define __NR_riscv_hwprobe (__NR_arch_specific_syscall + 14)
+#endif
+__SYSCALL(__NR_riscv_hwprobe, sys_riscv_hwprobe)
diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index 5d3f2fbeb33c..981d23457f13 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -6,8 +6,11 @@
  */
 
 #include <linux/syscalls.h>
-#include <asm/unistd.h>
 #include <asm/cacheflush.h>
+#include <asm/hwprobe.h>
+#include <asm/sbi.h>
+#include <asm/uaccess.h>
+#include <asm/unistd.h>
 #include <asm-generic/mman-common.h>
 
 static long riscv_sys_mmap(unsigned long addr, unsigned long len,
@@ -69,3 +72,134 @@ SYSCALL_DEFINE3(riscv_flush_icache, uintptr_t, start, uintptr_t, end,
 
 	return 0;
 }
+
+/*
+ * The hwprobe interface, for allowing userspace to probe to see which features
+ * are supported by the hardware.  See Documentation/riscv/hwprobe.rst for more
+ * details.
+ */
+static void hwprobe_arch_id(struct riscv_hwprobe *pair,
+			    const struct cpumask *cpus)
+{
+	u64 id = -1ULL;
+	bool first = true;
+	int cpu;
+
+	for_each_cpu(cpu, cpus) {
+		u64 cpu_id;
+
+		switch (pair->key) {
+		case RISCV_HWPROBE_KEY_MVENDORID:
+			cpu_id = riscv_cached_mvendorid(cpu);
+			break;
+		case RISCV_HWPROBE_KEY_MIMPID:
+			cpu_id = riscv_cached_mimpid(cpu);
+			break;
+		case RISCV_HWPROBE_KEY_MARCHID:
+			cpu_id = riscv_cached_marchid(cpu);
+			break;
+		}
+
+		if (first)
+			id = cpu_id;
+
+		/*
+		 * If there's a mismatch for the given set, return -1 in the
+		 * value.
+		 */
+		if (id != cpu_id) {
+			id = -1ULL;
+			break;
+		}
+	}
+
+	pair->value = id;
+}
+
+static void hwprobe_one_pair(struct riscv_hwprobe *pair,
+			     const struct cpumask *cpus)
+{
+	switch (pair->key) {
+	case RISCV_HWPROBE_KEY_MVENDORID:
+	case RISCV_HWPROBE_KEY_MARCHID:
+	case RISCV_HWPROBE_KEY_MIMPID:
+		hwprobe_arch_id(pair, cpus);
+		break;
+
+	/*
+	 * For forward compatibility, unknown keys don't fail the whole
+	 * call, but get their element key set to -1 and value set to 0
+	 * indicating they're unrecognized.
+	 */
+	default:
+		pair->key = -1;
+		pair->value = 0;
+		break;
+	}
+}
+
+static int do_riscv_hwprobe(struct riscv_hwprobe __user *pairs,
+			    size_t pair_count, size_t cpu_count,
+			    unsigned long __user *cpus_user,
+			    unsigned int flags)
+{
+	size_t out;
+	int ret;
+	cpumask_t cpus;
+
+	/* Check the reserved flags. */
+	if (flags != 0)
+		return -EINVAL;
+
+	/*
+	 * The interface supports taking in a CPU mask, and returns values that
+	 * are consistent across that mask. Allow userspace to specify NULL and
+	 * 0 as a shortcut to all online CPUs.
+	 */
+	cpumask_clear(&cpus);
+	if (!cpu_count && !cpus_user) {
+		cpumask_copy(&cpus, cpu_online_mask);
+	} else {
+		if (cpu_count > cpumask_size())
+			cpu_count = cpumask_size();
+
+		ret = copy_from_user(&cpus, cpus_user, cpu_count);
+		if (ret)
+			return -EFAULT;
+
+		/*
+		 * Userspace must provide at least one online CPU, without that
+		 * there's no way to define what is supported.
+		 */
+		cpumask_and(&cpus, &cpus, cpu_online_mask);
+		if (cpumask_empty(&cpus))
+			return -EINVAL;
+	}
+
+	for (out = 0; out < pair_count; out++, pairs++) {
+		struct riscv_hwprobe pair;
+
+		if (get_user(pair.key, &pairs->key))
+			return -EFAULT;
+
+		pair.value = 0;
+		hwprobe_one_pair(&pair, &cpus);
+		ret = put_user(pair.key, &pairs->key);
+		if (ret == 0)
+			ret = put_user(pair.value, &pairs->value);
+
+		if (ret)
+			return -EFAULT;
+	}
+
+	return 0;
+
+}
+
+SYSCALL_DEFINE5(riscv_hwprobe, struct riscv_hwprobe __user *, pairs,
+		size_t, pair_count, size_t, cpu_count, unsigned long __user *,
+		cpus, unsigned int, flags)
+{
+	return do_riscv_hwprobe(pairs, pair_count, cpu_count,
+				cpus, flags);
+}
-- 
2.25.1

[PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA

[Evan Green]

We have an implicit set of base behaviors that userspace depends on,
which are mostly defined in various ISA specifications.

Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Evan Green <evan@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
---

Changes in v4:
 - More newlines in BASE_BEHAVIOR_IMA documentation (Conor)

Changes in v3:
 - Refactored base ISA behavior probe to allow kernel probing as well,
   in prep for vDSO data initialization.
 - Fixed doc warnings in IMA text list, use :c:macro:.

 Documentation/riscv/hwprobe.rst       | 24 ++++++++++++++++++++++++
 arch/riscv/include/asm/hwprobe.h      |  2 +-
 arch/riscv/include/uapi/asm/hwprobe.h |  5 +++++
 arch/riscv/kernel/sys_riscv.c         | 20 ++++++++++++++++++++
 4 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
index 211828f706e3..945d44683c40 100644
--- a/Documentation/riscv/hwprobe.rst
+++ b/Documentation/riscv/hwprobe.rst
@@ -39,3 +39,27 @@ The following keys are defined:
 
 * :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as
   defined by the RISC-V privileged architecture specification.
+
+* :c:macro:`RISCV_HWPROBE_KEY_BASE_BEHAVIOR`: A bitmask containing the base
+  user-visible behavior that this kernel supports.  The following base user ABIs
+  are defined:
+
+  * :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`: Support for rv32ima or
+    rv64ima, as defined by version 2.2 of the user ISA and version 1.10 of the
+    privileged ISA, with the following known exceptions (more exceptions may be
+    added, but only if it can be demonstrated that the user ABI is not broken):
+
+    * The :fence.i: instruction cannot be directly executed by userspace
+      programs (it may still be executed in userspace via a
+      kernel-controlled mechanism such as the vDSO).
+
+* :c:macro:`RISCV_HWPROBE_KEY_IMA_EXT_0`: A bitmask containing the extensions
+  that are compatible with the :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`:
+  base system behavior.
+
+  * :c:macro:`RISCV_HWPROBE_IMA_FD`: The F and D extensions are supported, as
+    defined by commit cd20cee ("FMIN/FMAX now implement
+    minimumNumber/maximumNumber, not minNum/maxNum") of the RISC-V ISA manual.
+
+  * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
+    by version 2.2 of the RISC-V ISA manual.
diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
index 08d1c3bdd78a..7e52f1e1fe10 100644
--- a/arch/riscv/include/asm/hwprobe.h
+++ b/arch/riscv/include/asm/hwprobe.h
@@ -8,6 +8,6 @@
 
 #include <uapi/asm/hwprobe.h>
 
-#define RISCV_HWPROBE_MAX_KEY 2
+#define RISCV_HWPROBE_MAX_KEY 4
 
 #endif
diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
index 591802047460..fc5665411782 100644
--- a/arch/riscv/include/uapi/asm/hwprobe.h
+++ b/arch/riscv/include/uapi/asm/hwprobe.h
@@ -20,6 +20,11 @@ struct riscv_hwprobe {
 #define RISCV_HWPROBE_KEY_MVENDORID	0
 #define RISCV_HWPROBE_KEY_MARCHID	1
 #define RISCV_HWPROBE_KEY_MIMPID	2
+#define RISCV_HWPROBE_KEY_BASE_BEHAVIOR	3
+#define		RISCV_HWPROBE_BASE_BEHAVIOR_IMA	(1 << 0)
+#define RISCV_HWPROBE_KEY_IMA_EXT_0	4
+#define		RISCV_HWPROBE_IMA_FD		(1 << 0)
+#define		RISCV_HWPROBE_IMA_C		(1 << 1)
 /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
 
 #endif
diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index 981d23457f13..1c118438b1b3 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -9,6 +9,7 @@
 #include <asm/cacheflush.h>
 #include <asm/hwprobe.h>
 #include <asm/sbi.h>
+#include <asm/switch_to.h>
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 #include <asm-generic/mman-common.h>
@@ -125,6 +126,25 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
 	case RISCV_HWPROBE_KEY_MIMPID:
 		hwprobe_arch_id(pair, cpus);
 		break;
+	/*
+	 * The kernel already assumes that the base single-letter ISA
+	 * extensions are supported on all harts, and only supports the
+	 * IMA base, so just cheat a bit here and tell that to
+	 * userspace.
+	 */
+	case RISCV_HWPROBE_KEY_BASE_BEHAVIOR:
+		pair->value = RISCV_HWPROBE_BASE_BEHAVIOR_IMA;
+		break;
+
+	case RISCV_HWPROBE_KEY_IMA_EXT_0:
+		pair->value = 0;
+		if (has_fpu())
+			pair->value |= RISCV_HWPROBE_IMA_FD;
+
+		if (elf_hwcap & RISCV_ISA_EXT_c)
+			pair->value |= RISCV_HWPROBE_IMA_C;
+
+		break;
 
 	/*
 	 * For forward compatibility, unknown keys don't fail the whole
-- 
2.25.1

[PATCH v4 4/6] RISC-V: hwprobe: Support probing of misaligned access performance

[Evan Green]

This allows userspace to select various routines to use based on the
performance of misaligned access on the target hardware.

Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Evan Green <evan@rivosinc.com>

---

Changes in v4:
 - Add newlines to CPUPERF_0 documentation (Conor)
 - Add UNSUPPORTED value (Conor)
 - Switched from DT to alternatives-based probing (Rob)
 - Crispen up cpu index type to always be int (Conor)

Changes in v3:
 - Have hwprobe_misaligned return int instead of long.
 - Constify cpumask pointer in hwprobe_misaligned()
 - Fix warnings in _PERF_O list documentation, use :c:macro:.
 - Move include cpufeature.h to misaligned patch.
 - Fix documentation mismatch for RISCV_HWPROBE_KEY_CPUPERF_0 (Conor)
 - Use for_each_possible_cpu() instead of NR_CPUS (Conor)
 - Break early in misaligned access iteration (Conor)
 - Increase MISALIGNED_MASK from 2 bits to 3 for possible UNSUPPORTED future
   value (Conor)

Changes in v2:
 - Fixed logic error in if(of_property_read_string...) that caused crash
 - Include cpufeature.h in cpufeature.h to avoid undeclared variable
   warning.
 - Added a _MASK define
 - Fix random checkpatch complaints

 Documentation/riscv/hwprobe.rst       | 21 ++++++++++++++++++++
 arch/riscv/errata/thead/errata.c      |  9 +++++++++
 arch/riscv/include/asm/alternative.h  |  5 +++++
 arch/riscv/include/asm/cpufeature.h   |  2 ++
 arch/riscv/include/asm/hwprobe.h      |  2 +-
 arch/riscv/include/uapi/asm/hwprobe.h |  7 +++++++
 arch/riscv/kernel/alternative.c       | 19 ++++++++++++++++++
 arch/riscv/kernel/cpufeature.c        |  3 +++
 arch/riscv/kernel/smpboot.c           |  1 +
 arch/riscv/kernel/sys_riscv.c         | 28 +++++++++++++++++++++++++++
 10 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
index 945d44683c40..9f0dd62dcb5d 100644
--- a/Documentation/riscv/hwprobe.rst
+++ b/Documentation/riscv/hwprobe.rst
@@ -63,3 +63,24 @@ The following keys are defined:
 
   * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
     by version 2.2 of the RISC-V ISA manual.
+
+* :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
+  information about the selected set of processors.
+
+  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNKNOWN`: The performance of misaligned
+    accesses is unknown.
+
+  * :c:macro:`RISCV_HWPROBE_MISALIGNED_EMULATED`: Misaligned accesses are
+    emulated via software, either in or below the kernel.  These accesses are
+    always extremely slow.
+
+  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SLOW`: Misaligned accesses are supported
+    in hardware, but are slower than the cooresponding aligned accesses
+    sequences.
+
+  * :c:macro:`RISCV_HWPROBE_MISALIGNED_FAST`: Misaligned accesses are supported
+    in hardware and are faster than the cooresponding aligned accesses
+    sequences.
+
+  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNSUPPORTED`: Misaligned accesses are
+    not supported at all and will generate a misaligned address fault.
diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
index fac5742d1c1e..f41a45af5607 100644
--- a/arch/riscv/errata/thead/errata.c
+++ b/arch/riscv/errata/thead/errata.c
@@ -10,7 +10,9 @@
 #include <linux/uaccess.h>
 #include <asm/alternative.h>
 #include <asm/cacheflush.h>
+#include <asm/cpufeature.h>
 #include <asm/errata_list.h>
+#include <asm/hwprobe.h>
 #include <asm/patch.h>
 #include <asm/vendorid_list.h>
 
@@ -108,3 +110,10 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al
 	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
 		local_flush_icache_all();
 }
+
+void thead_feature_probe_func(unsigned int cpu, unsigned long archid,
+			      unsigned long impid)
+{
+	if ((archid == 0) && (impid == 0))
+		per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
+}
diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
index 6511dd73e812..7be6d4c6a27d 100644
--- a/arch/riscv/include/asm/alternative.h
+++ b/arch/riscv/include/asm/alternative.h
@@ -23,6 +23,7 @@
 #define RISCV_ALTERNATIVES_MODULE	1 /* alternatives applied during module-init */
 #define RISCV_ALTERNATIVES_EARLY_BOOT	2 /* alternatives applied before mmu start */
 
+void probe_vendor_features(unsigned int cpu);
 void __init apply_boot_alternatives(void);
 void __init apply_early_boot_alternatives(void);
 void apply_module_alternatives(void *start, size_t length);
@@ -47,11 +48,15 @@ void thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
 			     unsigned long archid, unsigned long impid,
 			     unsigned int stage);
 
+void thead_feature_probe_func(unsigned int cpu, unsigned long archid,
+			      unsigned long impid);
+
 void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end,
 				 unsigned int stage);
 
 #else /* CONFIG_RISCV_ALTERNATIVE */
 
+static inline void probe_vendor_features(unsigned int cpu) { }
 static inline void apply_boot_alternatives(void) { }
 static inline void apply_early_boot_alternatives(void) { }
 static inline void apply_module_alternatives(void *start, size_t length) { }
diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 66ebaae449c8..808d5403f2ac 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -18,4 +18,6 @@ struct riscv_cpuinfo {
 
 DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
 
+DECLARE_PER_CPU(long, misaligned_access_speed);
+
 #endif
diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
index 7e52f1e1fe10..4e45e33015bc 100644
--- a/arch/riscv/include/asm/hwprobe.h
+++ b/arch/riscv/include/asm/hwprobe.h
@@ -8,6 +8,6 @@
 
 #include <uapi/asm/hwprobe.h>
 
-#define RISCV_HWPROBE_MAX_KEY 4
+#define RISCV_HWPROBE_MAX_KEY 5
 
 #endif
diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
index fc5665411782..2968bb0984b5 100644
--- a/arch/riscv/include/uapi/asm/hwprobe.h
+++ b/arch/riscv/include/uapi/asm/hwprobe.h
@@ -25,6 +25,13 @@ struct riscv_hwprobe {
 #define RISCV_HWPROBE_KEY_IMA_EXT_0	4
 #define		RISCV_HWPROBE_IMA_FD		(1 << 0)
 #define		RISCV_HWPROBE_IMA_C		(1 << 1)
+#define RISCV_HWPROBE_KEY_CPUPERF_0	5
+#define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
+#define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
+#define		RISCV_HWPROBE_MISALIGNED_SLOW		(2 << 0)
+#define		RISCV_HWPROBE_MISALIGNED_FAST		(3 << 0)
+#define		RISCV_HWPROBE_MISALIGNED_UNSUPPORTED	(4 << 0)
+#define		RISCV_HWPROBE_MISALIGNED_MASK		(7 << 0)
 /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
 
 #endif
diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
index a7d26a00beea..522d3d11e0c3 100644
--- a/arch/riscv/kernel/alternative.c
+++ b/arch/riscv/kernel/alternative.c
@@ -23,6 +23,8 @@ struct cpu_manufacturer_info_t {
 	void (*patch_func)(struct alt_entry *begin, struct alt_entry *end,
 				  unsigned long archid, unsigned long impid,
 				  unsigned int stage);
+	void (*feature_probe_func)(unsigned int cpu, unsigned long archid,
+				   unsigned long impid);
 };
 
 static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_info_t *cpu_mfr_info)
@@ -37,6 +39,7 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
 	cpu_mfr_info->imp_id = sbi_get_mimpid();
 #endif
 
+	cpu_mfr_info->feature_probe_func = NULL;
 	switch (cpu_mfr_info->vendor_id) {
 #ifdef CONFIG_ERRATA_SIFIVE
 	case SIFIVE_VENDOR_ID:
@@ -46,6 +49,7 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
 #ifdef CONFIG_ERRATA_THEAD
 	case THEAD_VENDOR_ID:
 		cpu_mfr_info->patch_func = thead_errata_patch_func;
+		cpu_mfr_info->feature_probe_func = thead_feature_probe_func;
 		break;
 #endif
 	default:
@@ -53,6 +57,20 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
 	}
 }
 
+/* Called on each CPU as it starts */
+void probe_vendor_features(unsigned int cpu)
+{
+	struct cpu_manufacturer_info_t cpu_mfr_info;
+
+	riscv_fill_cpu_mfr_info(&cpu_mfr_info);
+	if (!cpu_mfr_info.feature_probe_func)
+		return;
+
+	cpu_mfr_info.feature_probe_func(cpu,
+					cpu_mfr_info.arch_id,
+					cpu_mfr_info.imp_id);
+}
+
 /*
  * This is called very early in the boot process (directly after we run
  * a feature detect on the boot CPU). No need to worry about other CPUs
@@ -82,6 +100,7 @@ void __init apply_boot_alternatives(void)
 	/* If called on non-boot cpu things could go wrong */
 	WARN_ON(smp_processor_id() != 0);
 
+	probe_vendor_features(0);
 	_apply_alternatives((struct alt_entry *)__alt_start,
 			    (struct alt_entry *)__alt_end,
 			    RISCV_ALTERNATIVES_BOOT);
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 93e45560af30..8ccf260e8b02 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -32,6 +32,9 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 DEFINE_STATIC_KEY_ARRAY_FALSE(riscv_isa_ext_keys, RISCV_ISA_EXT_KEY_MAX);
 EXPORT_SYMBOL(riscv_isa_ext_keys);
 
+/* Performance information */
+DEFINE_PER_CPU(long, misaligned_access_speed);
+
 /**
  * riscv_isa_extension_base() - Get base extension word
  *
diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 3373df413c88..1291ab5ba4c3 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -167,6 +167,7 @@ asmlinkage __visible void smp_callin(void)
 	notify_cpu_starting(curr_cpuid);
 	numa_add_cpu(curr_cpuid);
 	set_cpu_online(curr_cpuid, 1);
+	probe_vendor_features(curr_cpuid);
 
 	/*
 	 * Remote TLB flushes are ignored while the CPU is offline, so emit
diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index 1c118438b1b3..76d5b468914c 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -7,6 +7,7 @@
 
 #include <linux/syscalls.h>
 #include <asm/cacheflush.h>
+#include <asm/cpufeature.h>
 #include <asm/hwprobe.h>
 #include <asm/sbi.h>
 #include <asm/switch_to.h>
@@ -117,6 +118,29 @@ static void hwprobe_arch_id(struct riscv_hwprobe *pair,
 	pair->value = id;
 }
 
+static u64 hwprobe_misaligned(const struct cpumask *cpus)
+{
+	int cpu;
+	u64 perf = -1ULL;
+
+	for_each_cpu(cpu, cpus) {
+		int this_perf = per_cpu(misaligned_access_speed, cpu);
+
+		if (perf == -1ULL)
+			perf = this_perf;
+
+		if (perf != this_perf) {
+			perf = RISCV_HWPROBE_MISALIGNED_UNKNOWN;
+			break;
+		}
+	}
+
+	if (perf == -1ULL)
+		return RISCV_HWPROBE_MISALIGNED_UNKNOWN;
+
+	return perf;
+}
+
 static void hwprobe_one_pair(struct riscv_hwprobe *pair,
 			     const struct cpumask *cpus)
 {
@@ -146,6 +170,10 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
 
 		break;
 
+	case RISCV_HWPROBE_KEY_CPUPERF_0:
+		pair->value = hwprobe_misaligned(cpus);
+		break;
+
 	/*
 	 * For forward compatibility, unknown keys don't fail the whole
 	 * call, but get their element key set to -1 and value set to 0
-- 
2.25.1

Re: [PATCH v4 4/6] RISC-V: hwprobe: Support probing of misaligned access performance

[Heiko Stübner]

Hi Evan,

Am Dienstag, 14. März 2023, 19:32:18 CET schrieb Evan Green:
> This allows userspace to select various routines to use based on the
> performance of misaligned access on the target hardware.

I really like this implementation.

Also interesting that T-Head actually has a fast unaligned access.
Maybe that should be part of the commit message (including were
this information comes from)


> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>
> 
> ---
> 
> Changes in v4:
>  - Add newlines to CPUPERF_0 documentation (Conor)
>  - Add UNSUPPORTED value (Conor)
>  - Switched from DT to alternatives-based probing (Rob)
>  - Crispen up cpu index type to always be int (Conor)
> 
> Changes in v3:
>  - Have hwprobe_misaligned return int instead of long.
>  - Constify cpumask pointer in hwprobe_misaligned()
>  - Fix warnings in _PERF_O list documentation, use :c:macro:.
>  - Move include cpufeature.h to misaligned patch.
>  - Fix documentation mismatch for RISCV_HWPROBE_KEY_CPUPERF_0 (Conor)
>  - Use for_each_possible_cpu() instead of NR_CPUS (Conor)
>  - Break early in misaligned access iteration (Conor)
>  - Increase MISALIGNED_MASK from 2 bits to 3 for possible UNSUPPORTED future
>    value (Conor)
> 
> Changes in v2:
>  - Fixed logic error in if(of_property_read_string...) that caused crash
>  - Include cpufeature.h in cpufeature.h to avoid undeclared variable
>    warning.
>  - Added a _MASK define
>  - Fix random checkpatch complaints
> 
>  Documentation/riscv/hwprobe.rst       | 21 ++++++++++++++++++++
>  arch/riscv/errata/thead/errata.c      |  9 +++++++++
>  arch/riscv/include/asm/alternative.h  |  5 +++++
>  arch/riscv/include/asm/cpufeature.h   |  2 ++
>  arch/riscv/include/asm/hwprobe.h      |  2 +-
>  arch/riscv/include/uapi/asm/hwprobe.h |  7 +++++++
>  arch/riscv/kernel/alternative.c       | 19 ++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c        |  3 +++
>  arch/riscv/kernel/smpboot.c           |  1 +
>  arch/riscv/kernel/sys_riscv.c         | 28 +++++++++++++++++++++++++++
>  10 files changed, 96 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
> index 945d44683c40..9f0dd62dcb5d 100644
> --- a/Documentation/riscv/hwprobe.rst
> +++ b/Documentation/riscv/hwprobe.rst
> @@ -63,3 +63,24 @@ The following keys are defined:
>  
>    * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
>      by version 2.2 of the RISC-V ISA manual.
> +
> +* :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
> +  information about the selected set of processors.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNKNOWN`: The performance of misaligned
> +    accesses is unknown.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_EMULATED`: Misaligned accesses are
> +    emulated via software, either in or below the kernel.  These accesses are
> +    always extremely slow.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SLOW`: Misaligned accesses are supported
> +    in hardware, but are slower than the cooresponding aligned accesses
> +    sequences.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_FAST`: Misaligned accesses are supported
> +    in hardware and are faster than the cooresponding aligned accesses
> +    sequences.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNSUPPORTED`: Misaligned accesses are
> +    not supported at all and will generate a misaligned address fault.
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index fac5742d1c1e..f41a45af5607 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -10,7 +10,9 @@
>  #include <linux/uaccess.h>
>  #include <asm/alternative.h>
>  #include <asm/cacheflush.h>
> +#include <asm/cpufeature.h>
>  #include <asm/errata_list.h>
> +#include <asm/hwprobe.h>
>  #include <asm/patch.h>
>  #include <asm/vendorid_list.h>
>  
> @@ -108,3 +110,10 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al
>  	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
>  		local_flush_icache_all();
>  }
> +
> +void thead_feature_probe_func(unsigned int cpu, unsigned long archid,
> +			      unsigned long impid)
> +{
> +	if ((archid == 0) && (impid == 0))
> +		per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;

When looking at this function I 'm wondering if we also want to expose
the active erratas somehow (not in this patch of course, just in general)


Heiko

Re: [PATCH v4 4/6] RISC-V: hwprobe: Support probing of misaligned access performance

[Conor Dooley]

[-- Attachment #1: Type: text/plain, Size: 12375 bytes --]

On Tue, Mar 14, 2023 at 11:32:18AM -0700, Evan Green wrote:
> This allows userspace to select various routines to use based on the
> performance of misaligned access on the target hardware.
> 
> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>

I think this fine now, modulo the lack of an explanation in the commit
message for the new thead feature/"errata" that you've added.
With an explanation for that:
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Thanks,
Conor.

> ---
> 
> Changes in v4:
>  - Add newlines to CPUPERF_0 documentation (Conor)
>  - Add UNSUPPORTED value (Conor)
>  - Switched from DT to alternatives-based probing (Rob)
>  - Crispen up cpu index type to always be int (Conor)
> 
> Changes in v3:
>  - Have hwprobe_misaligned return int instead of long.
>  - Constify cpumask pointer in hwprobe_misaligned()
>  - Fix warnings in _PERF_O list documentation, use :c:macro:.
>  - Move include cpufeature.h to misaligned patch.
>  - Fix documentation mismatch for RISCV_HWPROBE_KEY_CPUPERF_0 (Conor)
>  - Use for_each_possible_cpu() instead of NR_CPUS (Conor)
>  - Break early in misaligned access iteration (Conor)
>  - Increase MISALIGNED_MASK from 2 bits to 3 for possible UNSUPPORTED future
>    value (Conor)
> 
> Changes in v2:
>  - Fixed logic error in if(of_property_read_string...) that caused crash
>  - Include cpufeature.h in cpufeature.h to avoid undeclared variable
>    warning.
>  - Added a _MASK define
>  - Fix random checkpatch complaints
> 
>  Documentation/riscv/hwprobe.rst       | 21 ++++++++++++++++++++
>  arch/riscv/errata/thead/errata.c      |  9 +++++++++
>  arch/riscv/include/asm/alternative.h  |  5 +++++
>  arch/riscv/include/asm/cpufeature.h   |  2 ++
>  arch/riscv/include/asm/hwprobe.h      |  2 +-
>  arch/riscv/include/uapi/asm/hwprobe.h |  7 +++++++
>  arch/riscv/kernel/alternative.c       | 19 ++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c        |  3 +++
>  arch/riscv/kernel/smpboot.c           |  1 +
>  arch/riscv/kernel/sys_riscv.c         | 28 +++++++++++++++++++++++++++
>  10 files changed, 96 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
> index 945d44683c40..9f0dd62dcb5d 100644
> --- a/Documentation/riscv/hwprobe.rst
> +++ b/Documentation/riscv/hwprobe.rst
> @@ -63,3 +63,24 @@ The following keys are defined:
>  
>    * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
>      by version 2.2 of the RISC-V ISA manual.
> +
> +* :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
> +  information about the selected set of processors.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNKNOWN`: The performance of misaligned
> +    accesses is unknown.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_EMULATED`: Misaligned accesses are
> +    emulated via software, either in or below the kernel.  These accesses are
> +    always extremely slow.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SLOW`: Misaligned accesses are supported
> +    in hardware, but are slower than the cooresponding aligned accesses
> +    sequences.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_FAST`: Misaligned accesses are supported
> +    in hardware and are faster than the cooresponding aligned accesses
> +    sequences.
> +
> +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNSUPPORTED`: Misaligned accesses are
> +    not supported at all and will generate a misaligned address fault.
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index fac5742d1c1e..f41a45af5607 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -10,7 +10,9 @@
>  #include <linux/uaccess.h>
>  #include <asm/alternative.h>
>  #include <asm/cacheflush.h>
> +#include <asm/cpufeature.h>
>  #include <asm/errata_list.h>
> +#include <asm/hwprobe.h>
>  #include <asm/patch.h>
>  #include <asm/vendorid_list.h>
>  
> @@ -108,3 +110,10 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al
>  	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
>  		local_flush_icache_all();
>  }
> +
> +void thead_feature_probe_func(unsigned int cpu, unsigned long archid,
> +			      unsigned long impid)
> +{
> +	if ((archid == 0) && (impid == 0))
> +		per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
> +}
> diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
> index 6511dd73e812..7be6d4c6a27d 100644
> --- a/arch/riscv/include/asm/alternative.h
> +++ b/arch/riscv/include/asm/alternative.h
> @@ -23,6 +23,7 @@
>  #define RISCV_ALTERNATIVES_MODULE	1 /* alternatives applied during module-init */
>  #define RISCV_ALTERNATIVES_EARLY_BOOT	2 /* alternatives applied before mmu start */
>  
> +void probe_vendor_features(unsigned int cpu);
>  void __init apply_boot_alternatives(void);
>  void __init apply_early_boot_alternatives(void);
>  void apply_module_alternatives(void *start, size_t length);
> @@ -47,11 +48,15 @@ void thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  			     unsigned long archid, unsigned long impid,
>  			     unsigned int stage);
>  
> +void thead_feature_probe_func(unsigned int cpu, unsigned long archid,
> +			      unsigned long impid);
> +
>  void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  				 unsigned int stage);
>  
>  #else /* CONFIG_RISCV_ALTERNATIVE */
>  
> +static inline void probe_vendor_features(unsigned int cpu) { }
>  static inline void apply_boot_alternatives(void) { }
>  static inline void apply_early_boot_alternatives(void) { }
>  static inline void apply_module_alternatives(void *start, size_t length) { }
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index 66ebaae449c8..808d5403f2ac 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -18,4 +18,6 @@ struct riscv_cpuinfo {
>  
>  DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
>  
> +DECLARE_PER_CPU(long, misaligned_access_speed);
> +
>  #endif
> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
> index 7e52f1e1fe10..4e45e33015bc 100644
> --- a/arch/riscv/include/asm/hwprobe.h
> +++ b/arch/riscv/include/asm/hwprobe.h
> @@ -8,6 +8,6 @@
>  
>  #include <uapi/asm/hwprobe.h>
>  
> -#define RISCV_HWPROBE_MAX_KEY 4
> +#define RISCV_HWPROBE_MAX_KEY 5
>  
>  #endif
> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> index fc5665411782..2968bb0984b5 100644
> --- a/arch/riscv/include/uapi/asm/hwprobe.h
> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> @@ -25,6 +25,13 @@ struct riscv_hwprobe {
>  #define RISCV_HWPROBE_KEY_IMA_EXT_0	4
>  #define		RISCV_HWPROBE_IMA_FD		(1 << 0)
>  #define		RISCV_HWPROBE_IMA_C		(1 << 1)
> +#define RISCV_HWPROBE_KEY_CPUPERF_0	5
> +#define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
> +#define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
> +#define		RISCV_HWPROBE_MISALIGNED_SLOW		(2 << 0)
> +#define		RISCV_HWPROBE_MISALIGNED_FAST		(3 << 0)
> +#define		RISCV_HWPROBE_MISALIGNED_UNSUPPORTED	(4 << 0)
> +#define		RISCV_HWPROBE_MISALIGNED_MASK		(7 << 0)
>  /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
>  
>  #endif
> diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
> index a7d26a00beea..522d3d11e0c3 100644
> --- a/arch/riscv/kernel/alternative.c
> +++ b/arch/riscv/kernel/alternative.c
> @@ -23,6 +23,8 @@ struct cpu_manufacturer_info_t {
>  	void (*patch_func)(struct alt_entry *begin, struct alt_entry *end,
>  				  unsigned long archid, unsigned long impid,
>  				  unsigned int stage);
> +	void (*feature_probe_func)(unsigned int cpu, unsigned long archid,
> +				   unsigned long impid);
>  };
>  
>  static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_info_t *cpu_mfr_info)
> @@ -37,6 +39,7 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
>  	cpu_mfr_info->imp_id = sbi_get_mimpid();
>  #endif
>  
> +	cpu_mfr_info->feature_probe_func = NULL;
>  	switch (cpu_mfr_info->vendor_id) {
>  #ifdef CONFIG_ERRATA_SIFIVE
>  	case SIFIVE_VENDOR_ID:
> @@ -46,6 +49,7 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
>  #ifdef CONFIG_ERRATA_THEAD
>  	case THEAD_VENDOR_ID:
>  		cpu_mfr_info->patch_func = thead_errata_patch_func;
> +		cpu_mfr_info->feature_probe_func = thead_feature_probe_func;
>  		break;
>  #endif
>  	default:
> @@ -53,6 +57,20 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
>  	}
>  }
>  
> +/* Called on each CPU as it starts */
> +void probe_vendor_features(unsigned int cpu)
> +{
> +	struct cpu_manufacturer_info_t cpu_mfr_info;
> +
> +	riscv_fill_cpu_mfr_info(&cpu_mfr_info);
> +	if (!cpu_mfr_info.feature_probe_func)
> +		return;
> +
> +	cpu_mfr_info.feature_probe_func(cpu,
> +					cpu_mfr_info.arch_id,
> +					cpu_mfr_info.imp_id);
> +}
> +
>  /*
>   * This is called very early in the boot process (directly after we run
>   * a feature detect on the boot CPU). No need to worry about other CPUs
> @@ -82,6 +100,7 @@ void __init apply_boot_alternatives(void)
>  	/* If called on non-boot cpu things could go wrong */
>  	WARN_ON(smp_processor_id() != 0);
>  
> +	probe_vendor_features(0);
>  	_apply_alternatives((struct alt_entry *)__alt_start,
>  			    (struct alt_entry *)__alt_end,
>  			    RISCV_ALTERNATIVES_BOOT);
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 93e45560af30..8ccf260e8b02 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -32,6 +32,9 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
>  DEFINE_STATIC_KEY_ARRAY_FALSE(riscv_isa_ext_keys, RISCV_ISA_EXT_KEY_MAX);
>  EXPORT_SYMBOL(riscv_isa_ext_keys);
>  
> +/* Performance information */
> +DEFINE_PER_CPU(long, misaligned_access_speed);
> +
>  /**
>   * riscv_isa_extension_base() - Get base extension word
>   *
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index 3373df413c88..1291ab5ba4c3 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -167,6 +167,7 @@ asmlinkage __visible void smp_callin(void)
>  	notify_cpu_starting(curr_cpuid);
>  	numa_add_cpu(curr_cpuid);
>  	set_cpu_online(curr_cpuid, 1);
> +	probe_vendor_features(curr_cpuid);
>  
>  	/*
>  	 * Remote TLB flushes are ignored while the CPU is offline, so emit
> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> index 1c118438b1b3..76d5b468914c 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -7,6 +7,7 @@
>  
>  #include <linux/syscalls.h>
>  #include <asm/cacheflush.h>
> +#include <asm/cpufeature.h>
>  #include <asm/hwprobe.h>
>  #include <asm/sbi.h>
>  #include <asm/switch_to.h>
> @@ -117,6 +118,29 @@ static void hwprobe_arch_id(struct riscv_hwprobe *pair,
>  	pair->value = id;
>  }
>  
> +static u64 hwprobe_misaligned(const struct cpumask *cpus)
> +{
> +	int cpu;
> +	u64 perf = -1ULL;
> +
> +	for_each_cpu(cpu, cpus) {
> +		int this_perf = per_cpu(misaligned_access_speed, cpu);
> +
> +		if (perf == -1ULL)
> +			perf = this_perf;
> +
> +		if (perf != this_perf) {
> +			perf = RISCV_HWPROBE_MISALIGNED_UNKNOWN;
> +			break;
> +		}
> +	}
> +
> +	if (perf == -1ULL)
> +		return RISCV_HWPROBE_MISALIGNED_UNKNOWN;
> +
> +	return perf;
> +}
> +
>  static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>  			     const struct cpumask *cpus)
>  {
> @@ -146,6 +170,10 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>  
>  		break;
>  
> +	case RISCV_HWPROBE_KEY_CPUPERF_0:
> +		pair->value = hwprobe_misaligned(cpus);
> +		break;
> +
>  	/*
>  	 * For forward compatibility, unknown keys don't fail the whole
>  	 * call, but get their element key set to -1 and value set to 0
> -- 
> 2.25.1
> 

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Re: [PATCH v4 4/6] RISC-V: hwprobe: Support probing of misaligned access performance

[Evan Green]

On Fri, Mar 17, 2023 at 3:08 AM Heiko Stübner <heiko@sntech.de> wrote:
>
> Hi Evan,
>
> Am Dienstag, 14. März 2023, 19:32:18 CET schrieb Evan Green:
> > This allows userspace to select various routines to use based on the
> > performance of misaligned access on the target hardware.
>
> I really like this implementation.
>
> Also interesting that T-Head actually has a fast unaligned access.
> Maybe that should be part of the commit message (including were
> this information comes from)

Thanks Heiko (and Conor)! Yep, you both noticed that, I'll add a description.

>
>
> > Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> > Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> > Signed-off-by: Evan Green <evan@rivosinc.com>
> >
> > ---
> >
> > Changes in v4:
> >  - Add newlines to CPUPERF_0 documentation (Conor)
> >  - Add UNSUPPORTED value (Conor)
> >  - Switched from DT to alternatives-based probing (Rob)
> >  - Crispen up cpu index type to always be int (Conor)
> >
> > Changes in v3:
> >  - Have hwprobe_misaligned return int instead of long.
> >  - Constify cpumask pointer in hwprobe_misaligned()
> >  - Fix warnings in _PERF_O list documentation, use :c:macro:.
> >  - Move include cpufeature.h to misaligned patch.
> >  - Fix documentation mismatch for RISCV_HWPROBE_KEY_CPUPERF_0 (Conor)
> >  - Use for_each_possible_cpu() instead of NR_CPUS (Conor)
> >  - Break early in misaligned access iteration (Conor)
> >  - Increase MISALIGNED_MASK from 2 bits to 3 for possible UNSUPPORTED future
> >    value (Conor)
> >
> > Changes in v2:
> >  - Fixed logic error in if(of_property_read_string...) that caused crash
> >  - Include cpufeature.h in cpufeature.h to avoid undeclared variable
> >    warning.
> >  - Added a _MASK define
> >  - Fix random checkpatch complaints
> >
> >  Documentation/riscv/hwprobe.rst       | 21 ++++++++++++++++++++
> >  arch/riscv/errata/thead/errata.c      |  9 +++++++++
> >  arch/riscv/include/asm/alternative.h  |  5 +++++
> >  arch/riscv/include/asm/cpufeature.h   |  2 ++
> >  arch/riscv/include/asm/hwprobe.h      |  2 +-
> >  arch/riscv/include/uapi/asm/hwprobe.h |  7 +++++++
> >  arch/riscv/kernel/alternative.c       | 19 ++++++++++++++++++
> >  arch/riscv/kernel/cpufeature.c        |  3 +++
> >  arch/riscv/kernel/smpboot.c           |  1 +
> >  arch/riscv/kernel/sys_riscv.c         | 28 +++++++++++++++++++++++++++
> >  10 files changed, 96 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
> > index 945d44683c40..9f0dd62dcb5d 100644
> > --- a/Documentation/riscv/hwprobe.rst
> > +++ b/Documentation/riscv/hwprobe.rst
> > @@ -63,3 +63,24 @@ The following keys are defined:
> >
> >    * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
> >      by version 2.2 of the RISC-V ISA manual.
> > +
> > +* :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
> > +  information about the selected set of processors.
> > +
> > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNKNOWN`: The performance of misaligned
> > +    accesses is unknown.
> > +
> > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_EMULATED`: Misaligned accesses are
> > +    emulated via software, either in or below the kernel.  These accesses are
> > +    always extremely slow.
> > +
> > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SLOW`: Misaligned accesses are supported
> > +    in hardware, but are slower than the cooresponding aligned accesses
> > +    sequences.
> > +
> > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_FAST`: Misaligned accesses are supported
> > +    in hardware and are faster than the cooresponding aligned accesses
> > +    sequences.
> > +
> > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNSUPPORTED`: Misaligned accesses are
> > +    not supported at all and will generate a misaligned address fault.
> > diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> > index fac5742d1c1e..f41a45af5607 100644
> > --- a/arch/riscv/errata/thead/errata.c
> > +++ b/arch/riscv/errata/thead/errata.c
> > @@ -10,7 +10,9 @@
> >  #include <linux/uaccess.h>
> >  #include <asm/alternative.h>
> >  #include <asm/cacheflush.h>
> > +#include <asm/cpufeature.h>
> >  #include <asm/errata_list.h>
> > +#include <asm/hwprobe.h>
> >  #include <asm/patch.h>
> >  #include <asm/vendorid_list.h>
> >
> > @@ -108,3 +110,10 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al
> >       if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> >               local_flush_icache_all();
> >  }
> > +
> > +void thead_feature_probe_func(unsigned int cpu, unsigned long archid,
> > +                           unsigned long impid)
> > +{
> > +     if ((archid == 0) && (impid == 0))
> > +             per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
>
> When looking at this function I 'm wondering if we also want to expose
> the active erratas somehow (not in this patch of course, just in general)

I suppose as Arnd pointed out in a different thread there's sort of a
tension between this mechanism and /proc/cpuinfo, the traditional spot
for exposing more standard cpu features/errata. Though if we think of
this mechanism as a sort of surrogate for cpuid, then it potentially
does make sense. My gut says it's a judgment call.

-Evan

Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA

[Heiko Stübner]

Hi Evan,

Am Dienstag, 14. März 2023, 19:32:17 CET schrieb Evan Green:
> We have an implicit set of base behaviors that userspace depends on,
> which are mostly defined in various ISA specifications.
> 
> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>
> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> ---
> 
> Changes in v4:
>  - More newlines in BASE_BEHAVIOR_IMA documentation (Conor)
> 
> Changes in v3:
>  - Refactored base ISA behavior probe to allow kernel probing as well,
>    in prep for vDSO data initialization.
>  - Fixed doc warnings in IMA text list, use :c:macro:.
> 
>  Documentation/riscv/hwprobe.rst       | 24 ++++++++++++++++++++++++
>  arch/riscv/include/asm/hwprobe.h      |  2 +-
>  arch/riscv/include/uapi/asm/hwprobe.h |  5 +++++
>  arch/riscv/kernel/sys_riscv.c         | 20 ++++++++++++++++++++
>  4 files changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
> index 211828f706e3..945d44683c40 100644
> --- a/Documentation/riscv/hwprobe.rst
> +++ b/Documentation/riscv/hwprobe.rst
> @@ -39,3 +39,27 @@ The following keys are defined:
>  
>  * :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as
>    defined by the RISC-V privileged architecture specification.
> +
> +* :c:macro:`RISCV_HWPROBE_KEY_BASE_BEHAVIOR`: A bitmask containing the base
> +  user-visible behavior that this kernel supports.  The following base user ABIs
> +  are defined:
> +
> +  * :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`: Support for rv32ima or
> +    rv64ima, as defined by version 2.2 of the user ISA and version 1.10 of the
> +    privileged ISA, with the following known exceptions (more exceptions may be
> +    added, but only if it can be demonstrated that the user ABI is not broken):
> +
> +    * The :fence.i: instruction cannot be directly executed by userspace
> +      programs (it may still be executed in userspace via a
> +      kernel-controlled mechanism such as the vDSO).
> +
> +* :c:macro:`RISCV_HWPROBE_KEY_IMA_EXT_0`: A bitmask containing the extensions
> +  that are compatible with the :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`:
> +  base system behavior.
> +
> +  * :c:macro:`RISCV_HWPROBE_IMA_FD`: The F and D extensions are supported, as
> +    defined by commit cd20cee ("FMIN/FMAX now implement
> +    minimumNumber/maximumNumber, not minNum/maxNum") of the RISC-V ISA manual.
> +
> +  * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
> +    by version 2.2 of the RISC-V ISA manual.

just wondering, is there a plan on how further extensions should be added this this?
[as we have this big plethora of them :-) ]

Aka things like Zbb and friends will probably also be relevant to userspace, so just
fill up RISCV_HWPROBE_KEY_IMA_EXT_0 with more elements and once full switch to
RISCV_HWPROBE_KEY_IMA_EXT_1 , RISCV_HWPROBE_KEY_IMA_EXT_2, etc?

Or do we have some more elaborate sorting mechanism?


Thanks
Heiko



> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
> index 08d1c3bdd78a..7e52f1e1fe10 100644
> --- a/arch/riscv/include/asm/hwprobe.h
> +++ b/arch/riscv/include/asm/hwprobe.h
> @@ -8,6 +8,6 @@
>  
>  #include <uapi/asm/hwprobe.h>
>  
> -#define RISCV_HWPROBE_MAX_KEY 2
> +#define RISCV_HWPROBE_MAX_KEY 4
>  
>  #endif
> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> index 591802047460..fc5665411782 100644
> --- a/arch/riscv/include/uapi/asm/hwprobe.h
> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> @@ -20,6 +20,11 @@ struct riscv_hwprobe {
>  #define RISCV_HWPROBE_KEY_MVENDORID	0
>  #define RISCV_HWPROBE_KEY_MARCHID	1
>  #define RISCV_HWPROBE_KEY_MIMPID	2
> +#define RISCV_HWPROBE_KEY_BASE_BEHAVIOR	3
> +#define		RISCV_HWPROBE_BASE_BEHAVIOR_IMA	(1 << 0)
> +#define RISCV_HWPROBE_KEY_IMA_EXT_0	4
> +#define		RISCV_HWPROBE_IMA_FD		(1 << 0)
> +#define		RISCV_HWPROBE_IMA_C		(1 << 1)
>  /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
>  
>  #endif
> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> index 981d23457f13..1c118438b1b3 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -9,6 +9,7 @@
>  #include <asm/cacheflush.h>
>  #include <asm/hwprobe.h>
>  #include <asm/sbi.h>
> +#include <asm/switch_to.h>
>  #include <asm/uaccess.h>
>  #include <asm/unistd.h>
>  #include <asm-generic/mman-common.h>
> @@ -125,6 +126,25 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>  	case RISCV_HWPROBE_KEY_MIMPID:
>  		hwprobe_arch_id(pair, cpus);
>  		break;
> +	/*
> +	 * The kernel already assumes that the base single-letter ISA
> +	 * extensions are supported on all harts, and only supports the
> +	 * IMA base, so just cheat a bit here and tell that to
> +	 * userspace.
> +	 */
> +	case RISCV_HWPROBE_KEY_BASE_BEHAVIOR:
> +		pair->value = RISCV_HWPROBE_BASE_BEHAVIOR_IMA;
> +		break;
> +
> +	case RISCV_HWPROBE_KEY_IMA_EXT_0:
> +		pair->value = 0;
> +		if (has_fpu())
> +			pair->value |= RISCV_HWPROBE_IMA_FD;
> +
> +		if (elf_hwcap & RISCV_ISA_EXT_c)
> +			pair->value |= RISCV_HWPROBE_IMA_C;
> +
> +		break;
>  
>  	/*
>  	 * For forward compatibility, unknown keys don't fail the whole
> 

Re: [PATCH v4 2/6] RISC-V: Add a syscall for HW probing

[Heiko Stübner]

Am Dienstag, 14. März 2023, 19:32:16 CET schrieb Evan Green:
> We don't have enough space for these all in ELF_HWCAP{,2} and there's no
> system call that quite does this, so let's just provide an arch-specific
> one to probe for hardware capabilities.  This currently just provides
> m{arch,imp,vendor}id, but with the key-value pairs we can pass more in
> the future.
> 
> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>
> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>

Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA

[Heiko Stübner]

Am Dienstag, 14. März 2023, 19:32:17 CET schrieb Evan Green:
> We have an implicit set of base behaviors that userspace depends on,
> which are mostly defined in various ISA specifications.
> 
> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>
> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

This needs one fix, described blow, with that applied:
Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>


> +	case RISCV_HWPROBE_KEY_IMA_EXT_0:
> +		pair->value = 0;
> +		if (has_fpu())
> +			pair->value |= RISCV_HWPROBE_IMA_FD;
> +
> +		if (elf_hwcap & RISCV_ISA_EXT_c)

This wants to be 
		if (elf_hwcap & riscv_isa_extension_mask(c))

i.e. elf_hwcap is a bitmap, RISCV_ISA_EXT_c is the number "2" and
riscv_isa_extension_mask() will get you the shifted bit.


> +			pair->value |= RISCV_HWPROBE_IMA_C;
> +
> +		break;
>  
>  	/*
>  	 * For forward compatibility, unknown keys don't fail the whole
> 

Heiko

Re: [PATCH v4 4/6] RISC-V: hwprobe: Support probing of misaligned access performance

[Heiko Stübner]

Am Dienstag, 14. März 2023, 19:32:18 CET schrieb Evan Green:
> This allows userspace to select various routines to use based on the
> performance of misaligned access on the target hardware.
> 
> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>

With the mentioned comment about the origin of the thead valie

Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>

Re: [PATCH v4 0/6] RISC-V Hardware Probing User Interface

[Heiko Stübner]

Am Dienstag, 14. März 2023, 19:32:14 CET schrieb Evan Green:
> 
> There's been a bunch of off-list discussions about this, including at
> Plumbers.  The original plan was to do something involving providing an
> ISA string to userspace, but ISA strings just aren't sufficient for a
> stable ABI any more: in order to parse an ISA string users need the
> version of the specifications that the string is written to, the version
> of each extension (sometimes at a finer granularity than the RISC-V
> releases/versions encode), and the expected use case for the ISA string
> (ie, is it a U-mode or M-mode string).  That's a lot of complexity to
> try and keep ABI compatible and it's probably going to continue to grow,
> as even if there's no more complexity in the specifications we'll have
> to deal with the various ISA string parsing oddities that end up all
> over userspace.
> 
> Instead this patch set takes a very different approach and provides a set
> of key/value pairs that encode various bits about the system.  The big
> advantage here is that we can clearly define what these mean so we can
> ensure ABI stability, but it also allows us to encode information that's
> unlikely to ever appear in an ISA string (see the misaligned access
> performance, for example).  The resulting interface looks a lot like
> what arm64 and x86 do, and will hopefully fit well into something like
> ACPI in the future.
> 
> The actual user interface is a syscall, with a vDSO function in front of
> it. The vDSO function can answer some queries without a syscall at all,
> and falls back to the syscall for cases it doesn't have answers to.
> Currently we prepopulate it with an array of answers for all keys and
> a CPU set of "all CPUs". This can be adjusted as necessary to provide
> fast answers to the most common queries.

I've built myself a small test-program [see below], to check the feature
on the d1-nezha board. Which is how I found the tiny c-extension issue.

Series works as expected there, so patches 1-4 on a d1-nezha:

Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu>



hwprobe.c:
----------------
#include <linux/types.h>
#include <sys/syscall.h>
#include <stdio.h>
#include <unistd.h>

#define __NR_riscv_hwprobe 258

struct riscv_hwprobe {
        __s64 key;
        __u64 value;
};

#define RISCV_HWPROBE_KEY_MVENDORID     0
#define RISCV_HWPROBE_KEY_MARCHID       1
#define RISCV_HWPROBE_KEY_MIMPID        2
#define RISCV_HWPROBE_KEY_BASE_BEHAVIOR 3
#define         RISCV_HWPROBE_BASE_BEHAVIOR_IMA (1 << 0)
#define RISCV_HWPROBE_KEY_IMA_EXT_0     4
#define         RISCV_HWPROBE_IMA_FD            (1 << 0)
#define         RISCV_HWPROBE_IMA_C             (1 << 1)
#define RISCV_HWPROBE_KEY_CPUPERF_0     5
#define         RISCV_HWPROBE_MISALIGNED_UNKNOWN        (0 << 0)
#define         RISCV_HWPROBE_MISALIGNED_EMULATED       (1 << 0)
#define         RISCV_HWPROBE_MISALIGNED_SLOW           (2 << 0)
#define         RISCV_HWPROBE_MISALIGNED_FAST           (3 << 0)
#define         RISCV_HWPROBE_MISALIGNED_UNSUPPORTED    (4 << 0)
#define         RISCV_HWPROBE_MISALIGNED_MASK           (7 << 0)

int __riscv_hwprobe (struct riscv_hwprobe *pairs, long pair_count,
  long cpu_count, unsigned long *cpus, unsigned long flags)
{

        return syscall(__NR_riscv_hwprobe, pairs, pair_count, cpu_count, cpus, flags);
}

int main(void)
{
        struct riscv_hwprobe pairs[3];

        pairs[0].key = RISCV_HWPROBE_KEY_MVENDORID;
        pairs[1].key = RISCV_HWPROBE_KEY_MARCHID;
        pairs[2].key = RISCV_HWPROBE_KEY_MIMPID;
        if (__riscv_hwprobe(pairs, 3, 0, NULL, 0) != 0) {
                printf("syscall failed");
                return -1;
        }

        printf("vendorid 0x%x, archid 0x%x, impid 0x%x\n",
               pairs[0].value, pairs[1].value, pairs[2].value);


        pairs[0].key = RISCV_HWPROBE_KEY_CPUPERF_0;
        pairs[1].key = RISCV_HWPROBE_KEY_BASE_BEHAVIOR;
        pairs[2].key = RISCV_HWPROBE_KEY_IMA_EXT_0;
        if (__riscv_hwprobe(&pairs[0], 3, 0, NULL, 0) != 0) {
                printf("syscall failed");
                return -1;
        }

        printf("ima-behavior %d, f+d %d, c %d, misaligned access: %s\n",
        ((pairs[1].value & RISCV_HWPROBE_BASE_BEHAVIOR_IMA) == RISCV_HWPROBE_BASE_BEHAVIOR_IMA),
        ((pairs[2].value & RISCV_HWPROBE_IMA_FD) == RISCV_HWPROBE_IMA_FD),
        ((pairs[2].value & RISCV_HWPROBE_IMA_C) == RISCV_HWPROBE_IMA_C),
        ((pairs[0].value & RISCV_HWPROBE_MISALIGNED_FAST) == RISCV_HWPROBE_MISALIGNED_FAST) ? "fast" : "not-fast"
        );

        return 0;
}

Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA

[Conor Dooley]

[-- Attachment #1: Type: text/plain, Size: 1573 bytes --]

On Tue, Mar 14, 2023 at 11:32:17AM -0700, Evan Green wrote:
> We have an implicit set of base behaviors that userspace depends on,
> which are mostly defined in various ISA specifications.
> 
> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>
> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

> @@ -125,6 +126,25 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>  	case RISCV_HWPROBE_KEY_MIMPID:
>  		hwprobe_arch_id(pair, cpus);
>  		break;
> +	/*
> +	 * The kernel already assumes that the base single-letter ISA
> +	 * extensions are supported on all harts, and only supports the
> +	 * IMA base, so just cheat a bit here and tell that to
> +	 * userspace.
> +	 */
> +	case RISCV_HWPROBE_KEY_BASE_BEHAVIOR:
> +		pair->value = RISCV_HWPROBE_BASE_BEHAVIOR_IMA;
> +		break;
> +
> +	case RISCV_HWPROBE_KEY_IMA_EXT_0:
> +		pair->value = 0;
> +		if (has_fpu())
> +			pair->value |= RISCV_HWPROBE_IMA_FD;
> +
> +		if (elf_hwcap & RISCV_ISA_EXT_c)

Random thought while reviewing another patch, and I kinda felt a bit
stupid following the existing code to try and make sure, but should this
become a call to riscv_isa_extension_available(NULL, c)?
It may be nice to propagate that helper, if it works, than check the bit
directly.

Cheers,
Conor.

> +			pair->value |= RISCV_HWPROBE_IMA_C;
> +
> +		break;
>  
>  	/*
>  	 * For forward compatibility, unknown keys don't fail the whole
> -- 
> 2.25.1
> 

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Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA

[Evan Green]

Yep, you and Heiko are on the same wavelength these days. I'll make that change.
-Evan

On Wed, Mar 22, 2023 at 8:36 AM Conor Dooley <conor@kernel.org> wrote:
>
> On Tue, Mar 14, 2023 at 11:32:17AM -0700, Evan Green wrote:
> > We have an implicit set of base behaviors that userspace depends on,
> > which are mostly defined in various ISA specifications.
> >
> > Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> > Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> > Signed-off-by: Evan Green <evan@rivosinc.com>
> > Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
>
> > @@ -125,6 +126,25 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
> >       case RISCV_HWPROBE_KEY_MIMPID:
> >               hwprobe_arch_id(pair, cpus);
> >               break;
> > +     /*
> > +      * The kernel already assumes that the base single-letter ISA
> > +      * extensions are supported on all harts, and only supports the
> > +      * IMA base, so just cheat a bit here and tell that to
> > +      * userspace.
> > +      */
> > +     case RISCV_HWPROBE_KEY_BASE_BEHAVIOR:
> > +             pair->value = RISCV_HWPROBE_BASE_BEHAVIOR_IMA;
> > +             break;
> > +
> > +     case RISCV_HWPROBE_KEY_IMA_EXT_0:
> > +             pair->value = 0;
> > +             if (has_fpu())
> > +                     pair->value |= RISCV_HWPROBE_IMA_FD;
> > +
> > +             if (elf_hwcap & RISCV_ISA_EXT_c)
>
> Random thought while reviewing another patch, and I kinda felt a bit
> stupid following the existing code to try and make sure, but should this
> become a call to riscv_isa_extension_available(NULL, c)?
> It may be nice to propagate that helper, if it works, than check the bit
> directly.
>
> Cheers,
> Conor.
>
> > +                     pair->value |= RISCV_HWPROBE_IMA_C;
> > +
> > +             break;
> >
> >       /*
> >        * For forward compatibility, unknown keys don't fail the whole
> > --
> > 2.25.1
> >

Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA

[Evan Green]

On Tue, Mar 21, 2023 at 9:41 AM Heiko Stübner <heiko@sntech.de> wrote:
>
> Hi Evan,
>
> Am Dienstag, 14. März 2023, 19:32:17 CET schrieb Evan Green:
> > We have an implicit set of base behaviors that userspace depends on,
> > which are mostly defined in various ISA specifications.
> >
> > Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> > Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> > Signed-off-by: Evan Green <evan@rivosinc.com>
> > Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> > ---
> >
> > Changes in v4:
> >  - More newlines in BASE_BEHAVIOR_IMA documentation (Conor)
> >
> > Changes in v3:
> >  - Refactored base ISA behavior probe to allow kernel probing as well,
> >    in prep for vDSO data initialization.
> >  - Fixed doc warnings in IMA text list, use :c:macro:.
> >
> >  Documentation/riscv/hwprobe.rst       | 24 ++++++++++++++++++++++++
> >  arch/riscv/include/asm/hwprobe.h      |  2 +-
> >  arch/riscv/include/uapi/asm/hwprobe.h |  5 +++++
> >  arch/riscv/kernel/sys_riscv.c         | 20 ++++++++++++++++++++
> >  4 files changed, 50 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
> > index 211828f706e3..945d44683c40 100644
> > --- a/Documentation/riscv/hwprobe.rst
> > +++ b/Documentation/riscv/hwprobe.rst
> > @@ -39,3 +39,27 @@ The following keys are defined:
> >
> >  * :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as
> >    defined by the RISC-V privileged architecture specification.
> > +
> > +* :c:macro:`RISCV_HWPROBE_KEY_BASE_BEHAVIOR`: A bitmask containing the base
> > +  user-visible behavior that this kernel supports.  The following base user ABIs
> > +  are defined:
> > +
> > +  * :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`: Support for rv32ima or
> > +    rv64ima, as defined by version 2.2 of the user ISA and version 1.10 of the
> > +    privileged ISA, with the following known exceptions (more exceptions may be
> > +    added, but only if it can be demonstrated that the user ABI is not broken):
> > +
> > +    * The :fence.i: instruction cannot be directly executed by userspace
> > +      programs (it may still be executed in userspace via a
> > +      kernel-controlled mechanism such as the vDSO).
> > +
> > +* :c:macro:`RISCV_HWPROBE_KEY_IMA_EXT_0`: A bitmask containing the extensions
> > +  that are compatible with the :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`:
> > +  base system behavior.
> > +
> > +  * :c:macro:`RISCV_HWPROBE_IMA_FD`: The F and D extensions are supported, as
> > +    defined by commit cd20cee ("FMIN/FMAX now implement
> > +    minimumNumber/maximumNumber, not minNum/maxNum") of the RISC-V ISA manual.
> > +
> > +  * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
> > +    by version 2.2 of the RISC-V ISA manual.
>
> just wondering, is there a plan on how further extensions should be added this this?
> [as we have this big plethora of them :-) ]
>
> Aka things like Zbb and friends will probably also be relevant to userspace, so just
> fill up RISCV_HWPROBE_KEY_IMA_EXT_0 with more elements and once full switch to
> RISCV_HWPROBE_KEY_IMA_EXT_1 , RISCV_HWPROBE_KEY_IMA_EXT_2, etc?
>
> Or do we have some more elaborate sorting mechanism?

That sounds reasonable to me. I tried to think about a couple of
possible sorting patterns, but when I played them out mentally they
were only ever aesthetically pleasing with no technical benefit, and
possibly added technical debt.
-Evan