From a7f4df4e21dd8a8dab96e88acd2c9c5017b83fc6 Mon Sep 17 00:00:00 2001 From: Alex Smith Date: Wed, 21 Oct 2015 09:57:44 +0100 Subject: 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/kernel/vdso.c | 71 ++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 65 insertions(+), 6 deletions(-) (limited to 'arch/mips/kernel/vdso.c') diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c index 56cc3c4..975e997 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) -- cgit v1.1