mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 10:49:33 +00:00
riscv: use vDSO common flow to reduce the latency of the time-related functions
Even if RISC-V has supported the vDSO feature, the latency of the functions for obtaining the system time is still expensive. It is because these functions still trigger a corresponding system call in the process, which slows down the response time. If we want to remove the system call to reduce the latency, the kernel should have the ability to output the system clock information to userspace. This patch introduces the vDSO common flow to enable the kernel to achieve the above feature and uses "rdtime" instruction to obtain the current time in the user space. Under this condition, the latency cost by the ecall from U-mode to S-mode can be eliminated. After applying this patch, the latency of gettimeofday() measured on the HiFive unleashed board can be reduced by %61. Signed-off-by: Vincent Chen <vincent.chen@sifive.com> Reviewed-by: Atish Patra <atish.patra@wdc.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
This commit is contained in:
parent
05589dde64
commit
ad5d1122b8
16 changed files with 199 additions and 69 deletions
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@ -12,6 +12,7 @@ config 32BIT
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config RISCV
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def_bool y
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select ARCH_CLOCKSOURCE_INIT
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select ARCH_HAS_BINFMT_FLAT
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select ARCH_HAS_DEBUG_VIRTUAL if MMU
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select ARCH_HAS_DEBUG_WX
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@ -31,6 +32,7 @@ config RISCV
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select GENERIC_ARCH_TOPOLOGY if SMP
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select GENERIC_ATOMIC64 if !64BIT
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select GENERIC_CLOCKEVENTS
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select GENERIC_GETTIMEOFDAY if HAVE_GENERIC_VDSO
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select GENERIC_IOREMAP
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select GENERIC_IRQ_MULTI_HANDLER
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select GENERIC_IRQ_SHOW
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@ -40,6 +42,7 @@ config RISCV
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select GENERIC_SMP_IDLE_THREAD
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select GENERIC_STRNCPY_FROM_USER if MMU
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select GENERIC_STRNLEN_USER if MMU
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select GENERIC_TIME_VSYSCALL if MMU && 64BIT
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select HANDLE_DOMAIN_IRQ
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select HAVE_ARCH_AUDITSYSCALL
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select HAVE_ARCH_KASAN if MMU && 64BIT
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@ -53,6 +56,7 @@ config RISCV
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select HAVE_DMA_CONTIGUOUS if MMU
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select HAVE_EBPF_JIT if MMU
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select HAVE_FUTEX_CMPXCHG if FUTEX
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select HAVE_GENERIC_VDSO if MMU && 64BIT
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select HAVE_PCI
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select HAVE_PERF_EVENTS
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select HAVE_PERF_REGS
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7
arch/riscv/include/asm/clocksource.h
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7
arch/riscv/include/asm/clocksource.h
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@ -0,0 +1,7 @@
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_CLOCKSOURCE_H
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#define _ASM_CLOCKSOURCE_H
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#include <asm/vdso/clocksource.h>
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#endif
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@ -8,6 +8,8 @@
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#include <linux/const.h>
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#include <vdso/processor.h>
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#include <asm/ptrace.h>
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/*
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@ -58,16 +60,6 @@ static inline void release_thread(struct task_struct *dead_task)
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extern unsigned long get_wchan(struct task_struct *p);
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static inline void cpu_relax(void)
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{
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#ifdef __riscv_muldiv
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int dummy;
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/* In lieu of a halt instruction, induce a long-latency stall. */
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__asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
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#endif
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barrier();
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}
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static inline void wait_for_interrupt(void)
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{
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__asm__ __volatile__ ("wfi");
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@ -10,8 +10,10 @@
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#include <linux/types.h>
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#ifndef GENERIC_TIME_VSYSCALL
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struct vdso_data {
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};
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#endif
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/*
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* The VDSO symbols are mapped into Linux so we can just use regular symbol
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8
arch/riscv/include/asm/vdso/clocksource.h
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arch/riscv/include/asm/vdso/clocksource.h
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@ -0,0 +1,8 @@
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_VDSOCLOCKSOURCE_H
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#define __ASM_VDSOCLOCKSOURCE_H
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#define VDSO_ARCH_CLOCKMODES \
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VDSO_CLOCKMODE_ARCHTIMER
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#endif
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79
arch/riscv/include/asm/vdso/gettimeofday.h
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arch/riscv/include/asm/vdso/gettimeofday.h
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@ -0,0 +1,79 @@
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_VDSO_GETTIMEOFDAY_H
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#define __ASM_VDSO_GETTIMEOFDAY_H
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#ifndef __ASSEMBLY__
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#include <asm/unistd.h>
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#include <asm/csr.h>
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#include <uapi/linux/time.h>
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#define VDSO_HAS_CLOCK_GETRES 1
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static __always_inline
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int gettimeofday_fallback(struct __kernel_old_timeval *_tv,
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struct timezone *_tz)
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{
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register struct __kernel_old_timeval *tv asm("a0") = _tv;
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register struct timezone *tz asm("a1") = _tz;
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register long ret asm("a0");
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register long nr asm("a7") = __NR_gettimeofday;
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asm volatile ("ecall\n"
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: "=r" (ret)
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: "r"(tv), "r"(tz), "r"(nr)
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: "memory");
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return ret;
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}
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static __always_inline
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long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
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{
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register clockid_t clkid asm("a0") = _clkid;
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register struct __kernel_timespec *ts asm("a1") = _ts;
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register long ret asm("a0");
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register long nr asm("a7") = __NR_clock_gettime;
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asm volatile ("ecall\n"
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: "=r" (ret)
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: "r"(clkid), "r"(ts), "r"(nr)
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: "memory");
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return ret;
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}
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static __always_inline
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int clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
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{
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register clockid_t clkid asm("a0") = _clkid;
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register struct __kernel_timespec *ts asm("a1") = _ts;
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register long ret asm("a0");
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register long nr asm("a7") = __NR_clock_getres;
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asm volatile ("ecall\n"
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: "=r" (ret)
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: "r"(clkid), "r"(ts), "r"(nr)
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: "memory");
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return ret;
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}
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static __always_inline u64 __arch_get_hw_counter(s32 clock_mode)
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{
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/*
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* The purpose of csr_read(CSR_TIME) is to trap the system into
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* M-mode to obtain the value of CSR_TIME. Hence, unlike other
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* architecture, no fence instructions surround the csr_read()
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*/
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return csr_read(CSR_TIME);
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}
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static __always_inline const struct vdso_data *__arch_get_vdso_data(void)
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{
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return _vdso_data;
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}
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#endif /* !__ASSEMBLY__ */
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#endif /* __ASM_VDSO_GETTIMEOFDAY_H */
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19
arch/riscv/include/asm/vdso/processor.h
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19
arch/riscv/include/asm/vdso/processor.h
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@ -0,0 +1,19 @@
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/* SPDX-License-Identifier: GPL-2.0-only */
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#ifndef __ASM_VDSO_PROCESSOR_H
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#define __ASM_VDSO_PROCESSOR_H
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#ifndef __ASSEMBLY__
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static inline void cpu_relax(void)
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{
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#ifdef __riscv_muldiv
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int dummy;
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/* In lieu of a halt instruction, induce a long-latency stall. */
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__asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
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#endif
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barrier();
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}
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#endif /* __ASSEMBLY__ */
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#endif /* __ASM_VDSO_PROCESSOR_H */
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arch/riscv/include/asm/vdso/vsyscall.h
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27
arch/riscv/include/asm/vdso/vsyscall.h
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@ -0,0 +1,27 @@
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_VDSO_VSYSCALL_H
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#define __ASM_VDSO_VSYSCALL_H
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#ifndef __ASSEMBLY__
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#include <linux/timekeeper_internal.h>
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#include <vdso/datapage.h>
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extern struct vdso_data *vdso_data;
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/*
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* Update the vDSO data page to keep in sync with kernel timekeeping.
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*/
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static __always_inline struct vdso_data *__riscv_get_k_vdso_data(void)
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{
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return vdso_data;
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}
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#define __arch_get_k_vdso_data __riscv_get_k_vdso_data
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/* The asm-generic header needs to be included after the definitions above */
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#include <asm-generic/vdso/vsyscall.h>
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#endif /* !__ASSEMBLY__ */
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#endif /* __ASM_VDSO_VSYSCALL_H */
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@ -26,3 +26,12 @@ void __init time_init(void)
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lpj_fine = riscv_timebase / HZ;
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timer_probe();
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}
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void clocksource_arch_init(struct clocksource *cs)
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{
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#ifdef CONFIG_GENERIC_GETTIMEOFDAY
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cs->vdso_clock_mode = VDSO_CLOCKMODE_ARCHTIMER;
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#else
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cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
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#endif
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}
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@ -11,8 +11,12 @@
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#include <linux/slab.h>
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#include <linux/binfmts.h>
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#include <linux/err.h>
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#include <asm/page.h>
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#ifdef GENERIC_TIME_VSYSCALL
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#include <vdso/datapage.h>
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#else
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#include <asm/vdso.h>
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#endif
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extern char vdso_start[], vdso_end[];
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@ -26,7 +30,7 @@ static union {
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struct vdso_data data;
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u8 page[PAGE_SIZE];
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} vdso_data_store __page_aligned_data;
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static struct vdso_data *vdso_data = &vdso_data_store.data;
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struct vdso_data *vdso_data = &vdso_data_store.data;
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static int __init vdso_init(void)
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{
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@ -1,12 +1,14 @@
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# SPDX-License-Identifier: GPL-2.0-only
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# Copied from arch/tile/kernel/vdso/Makefile
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# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
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# the inclusion of generic Makefile.
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ARCH_REL_TYPE_ABS := R_RISCV_32|R_RISCV_64|R_RISCV_JUMP_SLOT
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include $(srctree)/lib/vdso/Makefile
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# Symbols present in the vdso
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vdso-syms = rt_sigreturn
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ifdef CONFIG_64BIT
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vdso-syms += gettimeofday
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vdso-syms += clock_gettime
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vdso-syms += clock_getres
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vdso-syms += vgettimeofday
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endif
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vdso-syms += getcpu
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vdso-syms += flush_icache
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# Files to link into the vdso
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obj-vdso = $(patsubst %, %.o, $(vdso-syms)) note.o
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ifneq ($(c-gettimeofday-y),)
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CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
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endif
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# Build rules
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targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.lds vdso-dummy.o
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obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
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@ -1,18 +0,0 @@
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/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2017 SiFive
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*/
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#include <linux/linkage.h>
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#include <asm/unistd.h>
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.text
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/* int __vdso_clock_getres(clockid_t clock_id, struct timespec *res); */
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ENTRY(__vdso_clock_getres)
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.cfi_startproc
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/* For now, just do the syscall. */
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li a7, __NR_clock_getres
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ecall
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ret
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.cfi_endproc
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ENDPROC(__vdso_clock_getres)
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@ -1,18 +0,0 @@
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/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2017 SiFive
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*/
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#include <linux/linkage.h>
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#include <asm/unistd.h>
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.text
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/* int __vdso_clock_gettime(clockid_t clock_id, struct timespec *tp); */
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ENTRY(__vdso_clock_gettime)
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.cfi_startproc
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/* For now, just do the syscall. */
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li a7, __NR_clock_gettime
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ecall
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ret
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.cfi_endproc
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ENDPROC(__vdso_clock_gettime)
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@ -1,18 +0,0 @@
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/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2017 SiFive
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*/
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#include <linux/linkage.h>
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#include <asm/unistd.h>
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.text
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/* int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz); */
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ENTRY(__vdso_gettimeofday)
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.cfi_startproc
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/* For now, just do the syscall. */
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li a7, __NR_gettimeofday
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ecall
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ret
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.cfi_endproc
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ENDPROC(__vdso_gettimeofday)
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@ -2,11 +2,13 @@
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/*
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* Copyright (C) 2012 Regents of the University of California
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*/
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#include <asm/page.h>
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OUTPUT_ARCH(riscv)
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SECTIONS
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{
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PROVIDE(_vdso_data = . + PAGE_SIZE);
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. = SIZEOF_HEADERS;
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.hash : { *(.hash) } :text
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25
arch/riscv/kernel/vdso/vgettimeofday.c
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25
arch/riscv/kernel/vdso/vgettimeofday.c
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Copied from arch/arm64/kernel/vdso/vgettimeofday.c
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*
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* Copyright (C) 2018 ARM Ltd.
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* Copyright (C) 2020 SiFive
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*/
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#include <linux/time.h>
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#include <linux/types.h>
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int __vdso_clock_gettime(clockid_t clock, struct __kernel_timespec *ts)
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{
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return __cvdso_clock_gettime(clock, ts);
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}
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int __vdso_gettimeofday(struct __kernel_old_timeval *tv, struct timezone *tz)
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{
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return __cvdso_gettimeofday(tv, tz);
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}
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int __vdso_clock_getres(clockid_t clock_id, struct __kernel_timespec *res)
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{
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return __cvdso_clock_getres(clock_id, res);
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}
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