Unverified Commit aa5af0aa authored by Evan Green's avatar Evan Green Committed by Palmer Dabbelt
Browse files

RISC-V: Add hwprobe vDSO function and data 



Add a vDSO function __vdso_riscv_hwprobe, which can sit in front of the
riscv_hwprobe syscall and answer common queries. We stash a copy of
static answers for the "all CPUs" case in the vDSO data page. This data
is private to the vDSO, so we can decide later to change what's stored
there or under what conditions we defer to the syscall. Currently all
data can be discovered at boot, so the vDSO function answers all queries
when the cpumask is set to the "all CPUs" hint.

There's also a boolean in the data that lets the vDSO function know that
all CPUs are the same. In that case, the vDSO will also answer queries
for arbitrary CPU masks in addition to the "all CPUs" hint.

Signed-off-by: default avatarEvan Green <evan@rivosinc.com>
Link: https://lore.kernel.org/r/20230407231103.2622178-7-evan@rivosinc.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 287dcc2b

arch/riscv/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ config RISCV 
	select ARCH_HAS_STRICT_MODULE_RWX if MMU && !XIP_KERNEL

	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST

	select ARCH_HAS_UBSAN_SANITIZE_ALL

	select ARCH_HAS_VDSO_DATA

	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX

	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT

	select ARCH_STACKWALK

arch/riscv/include/asm/vdso/data.h

0 → 100644
+17 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef __RISCV_ASM_VDSO_DATA_H

#define __RISCV_ASM_VDSO_DATA_H



#include <linux/types.h>

#include <vdso/datapage.h>

#include <asm/hwprobe.h>



struct arch_vdso_data {

	/* Stash static answers to the hwprobe queries when all CPUs are selected. */

	__u64 all_cpu_hwprobe_values[RISCV_HWPROBE_MAX_KEY + 1];



	/* Boolean indicating all CPUs have the same static hwprobe values. */

	__u8 homogeneous_cpus;

};



#endif /* __RISCV_ASM_VDSO_DATA_H */

arch/riscv/include/asm/vdso/gettimeofday.h

+8 −0
Original line number Diff line number Diff line
@@ -9,6 +9,12 @@ 
#include <asm/csr.h>

#include <uapi/linux/time.h>



/*

 * 32-bit land is lacking generic time vsyscalls as well as the legacy 32-bit

 * time syscalls like gettimeofday. Skip these definitions since on 32-bit.

 */

#ifdef CONFIG_GENERIC_TIME_VSYSCALL



#define VDSO_HAS_CLOCK_GETRES	1



static __always_inline
@@ -60,6 +66,8 @@ int clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts) 
	return ret;

}



#endif /* CONFIG_GENERIC_TIME_VSYSCALL */



static __always_inline u64 __arch_get_hw_counter(s32 clock_mode,

						 const struct vdso_data *vd)

{

arch/riscv/kernel/compat_vdso/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -22,7 +22,7 @@ targets := $(obj-compat_vdso) compat_vdso.so compat_vdso.so.dbg compat_vdso.lds 
obj-compat_vdso := $(addprefix $(obj)/, $(obj-compat_vdso))



obj-y += compat_vdso.o

CPPFLAGS_compat_vdso.lds += -P -C -U$(ARCH)

CPPFLAGS_compat_vdso.lds += -P -C -DCOMPAT_VDSO -U$(ARCH)



# Disable profiling and instrumentation for VDSO code

GCOV_PROFILE := n

arch/riscv/kernel/sys_riscv.c

+45 −0
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#include <asm/uaccess.h>

#include <asm/unistd.h>

#include <asm-generic/mman-common.h>

#include <vdso/vsyscall.h>



static long riscv_sys_mmap(unsigned long addr, unsigned long len,

			   unsigned long prot, unsigned long flags,
@@ -243,6 +244,50 @@ static int do_riscv_hwprobe(struct riscv_hwprobe __user *pairs, 
	return 0;

}



#ifdef CONFIG_MMU



static int __init init_hwprobe_vdso_data(void)

{

	struct vdso_data *vd = __arch_get_k_vdso_data();

	struct arch_vdso_data *avd = &vd->arch_data;

	u64 id_bitsmash = 0;

	struct riscv_hwprobe pair;

	int key;



	/*

	 * Initialize vDSO data with the answers for the "all CPUs" case, to

	 * save a syscall in the common case.

	 */

	for (key = 0; key <= RISCV_HWPROBE_MAX_KEY; key++) {

		pair.key = key;

		hwprobe_one_pair(&pair, cpu_online_mask);



		WARN_ON_ONCE(pair.key < 0);



		avd->all_cpu_hwprobe_values[key] = pair.value;

		/*

		 * Smash together the vendor, arch, and impl IDs to see if

		 * they're all 0 or any negative.

		 */

		if (key <= RISCV_HWPROBE_KEY_MIMPID)

			id_bitsmash |= pair.value;

	}



	/*

	 * If the arch, vendor, and implementation ID are all the same across

	 * all harts, then assume all CPUs are the same, and allow the vDSO to

	 * answer queries for arbitrary masks. However if all values are 0 (not

	 * populated) or any value returns -1 (varies across CPUs), then the

	 * vDSO should defer to the kernel for exotic cpu masks.

	 */

	avd->homogeneous_cpus = (id_bitsmash > 0);

	return 0;

}



arch_initcall_sync(init_hwprobe_vdso_data);



#endif /* CONFIG_MMU */



SYSCALL_DEFINE5(riscv_hwprobe, struct riscv_hwprobe __user *, pairs,

		size_t, pair_count, size_t, cpu_count, unsigned long __user *,

		cpus, unsigned int, flags)