From a7f4df4e21dd8a8dab96e88acd2c9c5017b83fc6 Mon Sep 17 00:00:00 2001 From: Alex Smith Date: Wed, 21 Oct 2015 09:57:44 +0100 Subject: [PATCH] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime() Add user-mode implementations of gettimeofday() and clock_gettime() to the VDSO. This is currently usable with 2 clocksources: the CP0 count register, which is accessible to user-mode via RDHWR on R2 and later cores, or the MIPS Global Interrupt Controller (GIC) timer, which provides a "user-mode visible" section containing a mirror of its counter registers. This section must be mapped into user memory, which is done below the VDSO data page. When a supported clocksource is not in use, the VDSO functions will return -ENOSYS, which causes libc to fall back on the standard syscall path. When support for neither of these clocksources is compiled into the kernel at all, the VDSO still provides clock_gettime(), as the coarse realtime/monotonic clocks can still be implemented. However, gettimeofday() is not provided in this case as nothing can be done without a suitable clocksource. This causes the symbol lookup to fail in libc and it will then always use the standard syscall path. This patch includes a workaround for a bug in QEMU which results in RDHWR on the CP0 count register always returning a constant (incorrect) value. A fix for this has been submitted, and the workaround can be removed after the fix has been in stable releases for a reasonable amount of time. A simple performance test which calls gettimeofday() 1000 times in a loop and calculates the average execution time gives the following results on a Malta + I6400 (running at 20MHz): - Syscall: ~31000 ns - VDSO (GIC): ~15000 ns - VDSO (CP0): ~9500 ns [markos.chandras@imgtec.com: - Minor code re-arrangements in order for mappings to be made in the order they appear to the process' address space. - Move do_{monotonic, realtime} outside of the MIPS_CLOCK_VSYSCALL ifdef - Use gic_get_usm_range so we can do the GIC mapping in the arch/mips/kernel/vdso instead of the GIC irqchip driver] Signed-off-by: Alex Smith Signed-off-by: Markos Chandras Cc: linux-kernel@vger.kernel.org Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/11338/ Signed-off-by: Ralf Baechle --- arch/mips/Kconfig | 5 + arch/mips/include/asm/clocksource.h | 29 ++++ arch/mips/include/asm/vdso.h | 68 +++++++- arch/mips/kernel/csrc-r4k.c | 44 +++++ arch/mips/kernel/vdso.c | 71 +++++++- arch/mips/vdso/gettimeofday.c | 232 +++++++++++++++++++++++++++ arch/mips/vdso/vdso.h | 9 ++ arch/mips/vdso/vdso.lds.S | 5 + drivers/clocksource/mips-gic-timer.c | 7 +- 9 files changed, 460 insertions(+), 10 deletions(-) create mode 100644 arch/mips/include/asm/clocksource.h create mode 100644 arch/mips/vdso/gettimeofday.c diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index 9322d267e774..2f45c866e7ca 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -61,6 +61,8 @@ config MIPS select SYSCTL_EXCEPTION_TRACE select HAVE_VIRT_CPU_ACCOUNTING_GEN select HAVE_IRQ_TIME_ACCOUNTING + select GENERIC_TIME_VSYSCALL + select ARCH_CLOCKSOURCE_DATA menu "Machine selection" @@ -1040,6 +1042,9 @@ config CSRC_R4K config CSRC_SB1250 bool +config MIPS_CLOCK_VSYSCALL + def_bool CSRC_R4K || CLKSRC_MIPS_GIC + config GPIO_TXX9 select ARCH_REQUIRE_GPIOLIB bool diff --git a/arch/mips/include/asm/clocksource.h b/arch/mips/include/asm/clocksource.h new file mode 100644 index 000000000000..3deb1d0c1a94 --- /dev/null +++ b/arch/mips/include/asm/clocksource.h @@ -0,0 +1,29 @@ +/* + * Copyright (C) 2015 Imagination Technologies + * Author: Alex Smith + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License as published by the + * Free Software Foundation; either version 2 of the License, or (at your + * option) any later version. + */ + +#ifndef __ASM_CLOCKSOURCE_H +#define __ASM_CLOCKSOURCE_H + +#include + +/* VDSO clocksources. */ +#define VDSO_CLOCK_NONE 0 /* No suitable clocksource. */ +#define VDSO_CLOCK_R4K 1 /* Use the coprocessor 0 count. */ +#define VDSO_CLOCK_GIC 2 /* Use the GIC. */ + +/** + * struct arch_clocksource_data - Architecture-specific clocksource information. + * @vdso_clock_mode: Method the VDSO should use to access the clocksource. + */ +struct arch_clocksource_data { + u8 vdso_clock_mode; +}; + +#endif /* __ASM_CLOCKSOURCE_H */ diff --git a/arch/mips/include/asm/vdso.h b/arch/mips/include/asm/vdso.h index db2d45be8f2e..8f4ca5dd992b 100644 --- a/arch/mips/include/asm/vdso.h +++ b/arch/mips/include/asm/vdso.h @@ -13,6 +13,8 @@ #include +#include + /** * struct mips_vdso_image - Details of a VDSO image. * @data: Pointer to VDSO image data (page-aligned). @@ -53,18 +55,82 @@ extern struct mips_vdso_image vdso_image_n32; /** * union mips_vdso_data - Data provided by the kernel for the VDSO. + * @xtime_sec: Current real time (seconds part). + * @xtime_nsec: Current real time (nanoseconds part, shifted). + * @wall_to_mono_sec: Wall-to-monotonic offset (seconds part). + * @wall_to_mono_nsec: Wall-to-monotonic offset (nanoseconds part). + * @seq_count: Counter to synchronise updates (odd = updating). + * @cs_shift: Clocksource shift value. + * @clock_mode: Clocksource to use for time functions. + * @cs_mult: Clocksource multiplier value. + * @cs_cycle_last: Clock cycle value at last update. + * @cs_mask: Clocksource mask value. + * @tz_minuteswest: Minutes west of Greenwich (from timezone). + * @tz_dsttime: Type of DST correction (from timezone). * * This structure contains data needed by functions within the VDSO. It is - * populated by the kernel and mapped read-only into user memory. + * populated by the kernel and mapped read-only into user memory. The time + * fields are mirrors of internal data from the timekeeping infrastructure. * * Note: Care should be taken when modifying as the layout must remain the same * for both 64- and 32-bit (for 32-bit userland on 64-bit kernel). */ union mips_vdso_data { struct { + u64 xtime_sec; + u64 xtime_nsec; + u32 wall_to_mono_sec; + u32 wall_to_mono_nsec; + u32 seq_count; + u32 cs_shift; + u8 clock_mode; + u32 cs_mult; + u64 cs_cycle_last; + u64 cs_mask; + s32 tz_minuteswest; + s32 tz_dsttime; }; u8 page[PAGE_SIZE]; }; +static inline u32 vdso_data_read_begin(const union mips_vdso_data *data) +{ + u32 seq; + + while (true) { + seq = ACCESS_ONCE(data->seq_count); + if (likely(!(seq & 1))) { + /* Paired with smp_wmb() in vdso_data_write_*(). */ + smp_rmb(); + return seq; + } + + cpu_relax(); + } +} + +static inline bool vdso_data_read_retry(const union mips_vdso_data *data, + u32 start_seq) +{ + /* Paired with smp_wmb() in vdso_data_write_*(). */ + smp_rmb(); + return unlikely(data->seq_count != start_seq); +} + +static inline void vdso_data_write_begin(union mips_vdso_data *data) +{ + ++data->seq_count; + + /* Ensure sequence update is written before other data page values. */ + smp_wmb(); +} + +static inline void vdso_data_write_end(union mips_vdso_data *data) +{ + /* Ensure data values are written before updating sequence again. */ + smp_wmb(); + ++data->seq_count; +} + #endif /* __ASM_VDSO_H */ diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c index e5ed7ada1433..1f910563fdf6 100644 --- a/arch/mips/kernel/csrc-r4k.c +++ b/arch/mips/kernel/csrc-r4k.c @@ -28,6 +28,43 @@ static u64 notrace r4k_read_sched_clock(void) return read_c0_count(); } +static inline unsigned int rdhwr_count(void) +{ + unsigned int count; + + __asm__ __volatile__( + " .set push\n" + " .set mips32r2\n" + " rdhwr %0, $2\n" + " .set pop\n" + : "=r" (count)); + + return count; +} + +static bool rdhwr_count_usable(void) +{ + unsigned int prev, curr, i; + + /* + * Older QEMUs have a broken implementation of RDHWR for the CP0 count + * which always returns a constant value. Try to identify this and don't + * use it in the VDSO if it is broken. This workaround can be removed + * once the fix has been in QEMU stable for a reasonable amount of time. + */ + for (i = 0, prev = rdhwr_count(); i < 100; i++) { + curr = rdhwr_count(); + + if (curr != prev) + return true; + + prev = curr; + } + + pr_warn("Not using R4K clocksource in VDSO due to broken RDHWR\n"); + return false; +} + int __init init_r4k_clocksource(void) { if (!cpu_has_counter || !mips_hpt_frequency) @@ -36,6 +73,13 @@ int __init init_r4k_clocksource(void) /* Calculate a somewhat reasonable rating value */ clocksource_mips.rating = 200 + mips_hpt_frequency / 10000000; + /* + * R2 onwards makes the count accessible to user mode so it can be used + * by the VDSO (HWREna is configured by configure_hwrena()). + */ + if (cpu_has_mips_r2_r6 && rdhwr_count_usable()) + clocksource_mips.archdata.vdso_clock_mode = VDSO_CLOCK_R4K; + clocksource_register_hz(&clocksource_mips, mips_hpt_frequency); sched_clock_register(r4k_read_sched_clock, 32, mips_hpt_frequency); diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c index 56cc3c4377fb..975e99759bab 100644 --- a/arch/mips/kernel/vdso.c +++ b/arch/mips/kernel/vdso.c @@ -12,9 +12,12 @@ #include #include #include +#include +#include #include #include #include +#include #include #include @@ -23,7 +26,7 @@ static union mips_vdso_data vdso_data __page_aligned_data; /* - * Mapping for the VDSO data pages. The real pages are mapped manually, as + * Mapping for the VDSO data/GIC pages. The real pages are mapped manually, as * what we map and where within the area they are mapped is determined at * runtime. */ @@ -64,25 +67,67 @@ static int __init init_vdso(void) } subsys_initcall(init_vdso); +void update_vsyscall(struct timekeeper *tk) +{ + vdso_data_write_begin(&vdso_data); + + vdso_data.xtime_sec = tk->xtime_sec; + vdso_data.xtime_nsec = tk->tkr_mono.xtime_nsec; + vdso_data.wall_to_mono_sec = tk->wall_to_monotonic.tv_sec; + vdso_data.wall_to_mono_nsec = tk->wall_to_monotonic.tv_nsec; + vdso_data.cs_shift = tk->tkr_mono.shift; + + vdso_data.clock_mode = tk->tkr_mono.clock->archdata.vdso_clock_mode; + if (vdso_data.clock_mode != VDSO_CLOCK_NONE) { + vdso_data.cs_mult = tk->tkr_mono.mult; + vdso_data.cs_cycle_last = tk->tkr_mono.cycle_last; + vdso_data.cs_mask = tk->tkr_mono.mask; + } + + vdso_data_write_end(&vdso_data); +} + +void update_vsyscall_tz(void) +{ + if (vdso_data.clock_mode != VDSO_CLOCK_NONE) { + vdso_data.tz_minuteswest = sys_tz.tz_minuteswest; + vdso_data.tz_dsttime = sys_tz.tz_dsttime; + } +} + int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp) { struct mips_vdso_image *image = current->thread.abi->vdso; struct mm_struct *mm = current->mm; - unsigned long base, vdso_addr; + unsigned long gic_size, vvar_size, size, base, data_addr, vdso_addr; struct vm_area_struct *vma; + struct resource gic_res; int ret; down_write(&mm->mmap_sem); - base = get_unmapped_area(NULL, 0, PAGE_SIZE + image->size, 0, 0); + /* + * Determine total area size. This includes the VDSO data itself, the + * data page, and the GIC user page if present. Always create a mapping + * for the GIC user area if the GIC is present regardless of whether it + * is the current clocksource, in case it comes into use later on. We + * only map a page even though the total area is 64K, as we only need + * the counter registers at the start. + */ + gic_size = gic_present ? PAGE_SIZE : 0; + vvar_size = gic_size + PAGE_SIZE; + size = vvar_size + image->size; + + base = get_unmapped_area(NULL, 0, size, 0, 0); if (IS_ERR_VALUE(base)) { ret = base; goto out; } - vdso_addr = base + PAGE_SIZE; + data_addr = base + gic_size; + vdso_addr = data_addr + PAGE_SIZE; - vma = _install_special_mapping(mm, base, PAGE_SIZE, + vma = _install_special_mapping(mm, base, vvar_size, VM_READ | VM_MAYREAD, &vdso_vvar_mapping); if (IS_ERR(vma)) { @@ -90,8 +135,22 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp) goto out; } + /* Map GIC user page. */ + if (gic_size) { + ret = gic_get_usm_range(&gic_res); + if (ret) + goto out; + + ret = io_remap_pfn_range(vma, base, + gic_res.start >> PAGE_SHIFT, + gic_size, + pgprot_noncached(PAGE_READONLY)); + if (ret) + goto out; + } + /* Map data page. */ - ret = remap_pfn_range(vma, base, + ret = remap_pfn_range(vma, data_addr, virt_to_phys(&vdso_data) >> PAGE_SHIFT, PAGE_SIZE, PAGE_READONLY); if (ret) diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c new file mode 100644 index 000000000000..ce89c9e294f9 --- /dev/null +++ b/arch/mips/vdso/gettimeofday.c @@ -0,0 +1,232 @@ +/* + * Copyright (C) 2015 Imagination Technologies + * Author: Alex Smith + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License as published by the + * Free Software Foundation; either version 2 of the License, or (at your + * option) any later version. + */ + +#include "vdso.h" + +#include +#include +#include + +#include +#include +#include +#include +#include + +static __always_inline int do_realtime_coarse(struct timespec *ts, + const union mips_vdso_data *data) +{ + u32 start_seq; + + do { + start_seq = vdso_data_read_begin(data); + + ts->tv_sec = data->xtime_sec; + ts->tv_nsec = data->xtime_nsec >> data->cs_shift; + } while (vdso_data_read_retry(data, start_seq)); + + return 0; +} + +static __always_inline int do_monotonic_coarse(struct timespec *ts, + const union mips_vdso_data *data) +{ + u32 start_seq; + u32 to_mono_sec; + u32 to_mono_nsec; + + do { + start_seq = vdso_data_read_begin(data); + + ts->tv_sec = data->xtime_sec; + ts->tv_nsec = data->xtime_nsec >> data->cs_shift; + + to_mono_sec = data->wall_to_mono_sec; + to_mono_nsec = data->wall_to_mono_nsec; + } while (vdso_data_read_retry(data, start_seq)); + + ts->tv_sec += to_mono_sec; + timespec_add_ns(ts, to_mono_nsec); + + return 0; +} + +#ifdef CONFIG_CSRC_R4K + +static __always_inline u64 read_r4k_count(void) +{ + unsigned int count; + + __asm__ __volatile__( + " .set push\n" + " .set mips32r2\n" + " rdhwr %0, $2\n" + " .set pop\n" + : "=r" (count)); + + return count; +} + +#endif + +#ifdef CONFIG_CLKSRC_MIPS_GIC + +static __always_inline u64 read_gic_count(const union mips_vdso_data *data) +{ + void __iomem *gic = get_gic(data); + u32 hi, hi2, lo; + + do { + hi = __raw_readl(gic + GIC_UMV_SH_COUNTER_63_32_OFS); + lo = __raw_readl(gic + GIC_UMV_SH_COUNTER_31_00_OFS); + hi2 = __raw_readl(gic + GIC_UMV_SH_COUNTER_63_32_OFS); + } while (hi2 != hi); + + return (((u64)hi) << 32) + lo; +} + +#endif + +static __always_inline u64 get_ns(const union mips_vdso_data *data) +{ + u64 cycle_now, delta, nsec; + + switch (data->clock_mode) { +#ifdef CONFIG_CSRC_R4K + case VDSO_CLOCK_R4K: + cycle_now = read_r4k_count(); + break; +#endif +#ifdef CONFIG_CLKSRC_MIPS_GIC + case VDSO_CLOCK_GIC: + cycle_now = read_gic_count(data); + break; +#endif + default: + return 0; + } + + delta = (cycle_now - data->cs_cycle_last) & data->cs_mask; + + nsec = (delta * data->cs_mult) + data->xtime_nsec; + nsec >>= data->cs_shift; + + return nsec; +} + +static __always_inline int do_realtime(struct timespec *ts, + const union mips_vdso_data *data) +{ + u32 start_seq; + u64 ns; + + do { + start_seq = vdso_data_read_begin(data); + + if (data->clock_mode == VDSO_CLOCK_NONE) + return -ENOSYS; + + ts->tv_sec = data->xtime_sec; + ns = get_ns(data); + } while (vdso_data_read_retry(data, start_seq)); + + ts->tv_nsec = 0; + timespec_add_ns(ts, ns); + + return 0; +} + +static __always_inline int do_monotonic(struct timespec *ts, + const union mips_vdso_data *data) +{ + u32 start_seq; + u64 ns; + u32 to_mono_sec; + u32 to_mono_nsec; + + do { + start_seq = vdso_data_read_begin(data); + + if (data->clock_mode == VDSO_CLOCK_NONE) + return -ENOSYS; + + ts->tv_sec = data->xtime_sec; + ns = get_ns(data); + + to_mono_sec = data->wall_to_mono_sec; + to_mono_nsec = data->wall_to_mono_nsec; + } while (vdso_data_read_retry(data, start_seq)); + + ts->tv_sec += to_mono_sec; + ts->tv_nsec = 0; + timespec_add_ns(ts, ns + to_mono_nsec); + + return 0; +} + +#ifdef CONFIG_MIPS_CLOCK_VSYSCALL + +/* + * This is behind the ifdef so that we don't provide the symbol when there's no + * possibility of there being a usable clocksource, because there's nothing we + * can do without it. When libc fails the symbol lookup it should fall back on + * the standard syscall path. + */ +int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz) +{ + const union mips_vdso_data *data = get_vdso_data(); + struct timespec ts; + int ret; + + ret = do_realtime(&ts, data); + if (ret) + return ret; + + if (tv) { + tv->tv_sec = ts.tv_sec; + tv->tv_usec = ts.tv_nsec / 1000; + } + + if (tz) { + tz->tz_minuteswest = data->tz_minuteswest; + tz->tz_dsttime = data->tz_dsttime; + } + + return 0; +} + +#endif /* CONFIG_CLKSRC_MIPS_GIC */ + +int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts) +{ + const union mips_vdso_data *data = get_vdso_data(); + int ret; + + switch (clkid) { + case CLOCK_REALTIME_COARSE: + ret = do_realtime_coarse(ts, data); + break; + case CLOCK_MONOTONIC_COARSE: + ret = do_monotonic_coarse(ts, data); + break; + case CLOCK_REALTIME: + ret = do_realtime(ts, data); + break; + case CLOCK_MONOTONIC: + ret = do_monotonic(ts, data); + break; + default: + ret = -ENOSYS; + break; + } + + /* If we return -ENOSYS libc should fall back to a syscall. */ + return ret; +} diff --git a/arch/mips/vdso/vdso.h b/arch/mips/vdso/vdso.h index 0bb6b1adc385..cfb1be441dec 100644 --- a/arch/mips/vdso/vdso.h +++ b/arch/mips/vdso/vdso.h @@ -77,4 +77,13 @@ static inline const union mips_vdso_data *get_vdso_data(void) return (const union mips_vdso_data *)(get_vdso_base() - PAGE_SIZE); } +#ifdef CONFIG_CLKSRC_MIPS_GIC + +static inline void __iomem *get_gic(const union mips_vdso_data *data) +{ + return (void __iomem *)data - PAGE_SIZE; +} + +#endif /* CONFIG_CLKSRC_MIPS_GIC */ + #endif /* __ASSEMBLY__ */ diff --git a/arch/mips/vdso/vdso.lds.S b/arch/mips/vdso/vdso.lds.S index 21655b6fefc5..8df7dd53e8e0 100644 --- a/arch/mips/vdso/vdso.lds.S +++ b/arch/mips/vdso/vdso.lds.S @@ -95,6 +95,11 @@ PHDRS VERSION { LINUX_2.6 { +#ifndef DISABLE_MIPS_VDSO + global: + __vdso_clock_gettime; + __vdso_gettimeofday; +#endif local: *; }; } diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c index 02a1945e5093..89d3e4d7900c 100644 --- a/drivers/clocksource/mips-gic-timer.c +++ b/drivers/clocksource/mips-gic-timer.c @@ -140,9 +140,10 @@ static cycle_t gic_hpt_read(struct clocksource *cs) } static struct clocksource gic_clocksource = { - .name = "GIC", - .read = gic_hpt_read, - .flags = CLOCK_SOURCE_IS_CONTINUOUS, + .name = "GIC", + .read = gic_hpt_read, + .flags = CLOCK_SOURCE_IS_CONTINUOUS, + .archdata = { .vdso_clock_mode = VDSO_CLOCK_GIC }, }; static void __init __gic_clocksource_init(void) -- 2.39.5