--- /dev/null
+/*
+ * FP/SIMD context switching and fault handling
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/cpu_pm.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/signal.h>
+#include <linux/hardirq.h>
+
+#include <asm/fpsimd.h>
+#include <asm/cputype.h>
+
+#define FPEXC_IOF (1 << 0)
+#define FPEXC_DZF (1 << 1)
+#define FPEXC_OFF (1 << 2)
+#define FPEXC_UFF (1 << 3)
+#define FPEXC_IXF (1 << 4)
+#define FPEXC_IDF (1 << 7)
+
+/*
+ * In order to reduce the number of times the FPSIMD state is needlessly saved
+ * and restored, we need to keep track of two things:
+ * (a) for each task, we need to remember which CPU was the last one to have
+ * the task's FPSIMD state loaded into its FPSIMD registers;
+ * (b) for each CPU, we need to remember which task's userland FPSIMD state has
+ * been loaded into its FPSIMD registers most recently, or whether it has
+ * been used to perform kernel mode NEON in the meantime.
+ *
+ * For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
+ * the id of the current CPU everytime the state is loaded onto a CPU. For (b),
+ * we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
+ * address of the userland FPSIMD state of the task that was loaded onto the CPU
+ * the most recently, or NULL if kernel mode NEON has been performed after that.
+ *
+ * With this in place, we no longer have to restore the next FPSIMD state right
+ * when switching between tasks. Instead, we can defer this check to userland
+ * resume, at which time we verify whether the CPU's fpsimd_last_state and the
+ * task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
+ * can omit the FPSIMD restore.
+ *
+ * As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
+ * indicate whether or not the userland FPSIMD state of the current task is
+ * present in the registers. The flag is set unless the FPSIMD registers of this
+ * CPU currently contain the most recent userland FPSIMD state of the current
+ * task.
+ *
+ * For a certain task, the sequence may look something like this:
+ * - the task gets scheduled in; if both the task's fpsimd_state.cpu field
+ * contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
+ * variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
+ * cleared, otherwise it is set;
+ *
+ * - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
+ * userland FPSIMD state is copied from memory to the registers, the task's
+ * fpsimd_state.cpu field is set to the id of the current CPU, the current
+ * CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
+ * TIF_FOREIGN_FPSTATE flag is cleared;
+ *
+ * - the task executes an ordinary syscall; upon return to userland, the
+ * TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is
+ * restored;
+ *
+ * - the task executes a syscall which executes some NEON instructions; this is
+ * preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD
+ * register contents to memory, clears the fpsimd_last_state per-cpu variable
+ * and sets the TIF_FOREIGN_FPSTATE flag;
+ *
+ * - the task gets preempted after kernel_neon_end() is called; as we have not
+ * returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
+ * whatever is in the FPSIMD registers is not saved to memory, but discarded.
+ */
+static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
+
+/*
+ * Trapped FP/ASIMD access.
+ */
+void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
+{
+ /* TODO: implement lazy context saving/restoring */
+ WARN_ON(1);
+}
+
+/*
+ * Raise a SIGFPE for the current process.
+ */
+void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
+{
+ siginfo_t info;
+ unsigned int si_code = 0;
+
+ if (esr & FPEXC_IOF)
+ si_code = FPE_FLTINV;
+ else if (esr & FPEXC_DZF)
+ si_code = FPE_FLTDIV;
+ else if (esr & FPEXC_OFF)
+ si_code = FPE_FLTOVF;
+ else if (esr & FPEXC_UFF)
+ si_code = FPE_FLTUND;
+ else if (esr & FPEXC_IXF)
+ si_code = FPE_FLTRES;
+
+ memset(&info, 0, sizeof(info));
+ info.si_signo = SIGFPE;
+ info.si_code = si_code;
+ info.si_addr = (void __user *)instruction_pointer(regs);
+
+ send_sig_info(SIGFPE, &info, current);
+}
+
+void fpsimd_thread_switch(struct task_struct *next)
+{
+ /*
+ * Save the current FPSIMD state to memory, but only if whatever is in
+ * the registers is in fact the most recent userland FPSIMD state of
+ * 'current'.
+ */
+ if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
+ fpsimd_save_state(¤t->thread.fpsimd_state);
+
+ if (next->mm) {
+ /*
+ * If we are switching to a task whose most recent userland
+ * FPSIMD state is already in the registers of *this* cpu,
+ * we can skip loading the state from memory. Otherwise, set
+ * the TIF_FOREIGN_FPSTATE flag so the state will be loaded
+ * upon the next return to userland.
+ */
+ struct fpsimd_state *st = &next->thread.fpsimd_state;
+
+ if (__this_cpu_read(fpsimd_last_state) == st
+ && st->cpu == smp_processor_id())
+ clear_ti_thread_flag(task_thread_info(next),
+ TIF_FOREIGN_FPSTATE);
+ else
+ set_ti_thread_flag(task_thread_info(next),
+ TIF_FOREIGN_FPSTATE);
+ }
+}
+
+void fpsimd_flush_thread(void)
+{
+ memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
+ set_thread_flag(TIF_FOREIGN_FPSTATE);
+}
+
+/*
+ * Save the userland FPSIMD state of 'current' to memory, but only if the state
+ * currently held in the registers does in fact belong to 'current'
+ */
+void fpsimd_preserve_current_state(void)
+{
+ preempt_disable();
+ if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
+ fpsimd_save_state(¤t->thread.fpsimd_state);
+ preempt_enable();
+}
+
+/*
+ * Load the userland FPSIMD state of 'current' from memory, but only if the
+ * FPSIMD state already held in the registers is /not/ the most recent FPSIMD
+ * state of 'current'
+ */
+void fpsimd_restore_current_state(void)
+{
+ preempt_disable();
+ if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
+ struct fpsimd_state *st = ¤t->thread.fpsimd_state;
+
+ fpsimd_load_state(st);
+ this_cpu_write(fpsimd_last_state, st);
+ st->cpu = smp_processor_id();
+ }
+ preempt_enable();
+}
+
+/*
+ * Load an updated userland FPSIMD state for 'current' from memory and set the
+ * flag that indicates that the FPSIMD register contents are the most recent
+ * FPSIMD state of 'current'
+ */
+void fpsimd_update_current_state(struct fpsimd_state *state)
+{
+ preempt_disable();
+ fpsimd_load_state(state);
+ if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
+ struct fpsimd_state *st = ¤t->thread.fpsimd_state;
+
+ this_cpu_write(fpsimd_last_state, st);
+ st->cpu = smp_processor_id();
+ }
+ preempt_enable();
+}
+
+/*
+ * Invalidate live CPU copies of task t's FPSIMD state
+ */
+void fpsimd_flush_task_state(struct task_struct *t)
+{
+ t->thread.fpsimd_state.cpu = NR_CPUS;
+}
+
+#ifdef CONFIG_KERNEL_MODE_NEON
+
+static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate);
+static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate);
+
+/*
+ * Kernel-side NEON support functions
+ */
+void kernel_neon_begin_partial(u32 num_regs)
+{
+ if (in_interrupt()) {
+ struct fpsimd_partial_state *s = this_cpu_ptr(
+ in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
+
+ BUG_ON(num_regs > 32);
+ fpsimd_save_partial_state(s, roundup(num_regs, 2));
+ } else {
+ /*
+ * Save the userland FPSIMD state if we have one and if we
+ * haven't done so already. Clear fpsimd_last_state to indicate
+ * that there is no longer userland FPSIMD state in the
+ * registers.
+ */
+ preempt_disable();
+ if (current->mm &&
+ !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
+ fpsimd_save_state(¤t->thread.fpsimd_state);
+ this_cpu_write(fpsimd_last_state, NULL);
+ }
+}
+EXPORT_SYMBOL(kernel_neon_begin_partial);
+
+void kernel_neon_end(void)
+{
+ if (in_interrupt()) {
+ struct fpsimd_partial_state *s = this_cpu_ptr(
+ in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
+ fpsimd_load_partial_state(s);
+ } else {
+ preempt_enable();
+ }
+}
+EXPORT_SYMBOL(kernel_neon_end);
+
+#endif /* CONFIG_KERNEL_MODE_NEON */
+
+#ifdef CONFIG_CPU_PM
+static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
+ unsigned long cmd, void *v)
+{
+ switch (cmd) {
+ case CPU_PM_ENTER:
+ if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
+ fpsimd_save_state(¤t->thread.fpsimd_state);
+ this_cpu_write(fpsimd_last_state, NULL);
+ break;
+ case CPU_PM_EXIT:
+ if (current->mm)
+ set_thread_flag(TIF_FOREIGN_FPSTATE);
+ break;
+ case CPU_PM_ENTER_FAILED:
+ default:
+ return NOTIFY_DONE;
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block fpsimd_cpu_pm_notifier_block = {
+ .notifier_call = fpsimd_cpu_pm_notifier,
+};
+
+static void fpsimd_pm_init(void)
+{
+ cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block);
+}
+
+#else
+static inline void fpsimd_pm_init(void) { }
+#endif /* CONFIG_CPU_PM */
+
+/*
+ * FP/SIMD support code initialisation.
+ */
+static int __init fpsimd_init(void)
+{
+ u64 pfr = read_cpuid(ID_AA64PFR0_EL1);
+
+ if (pfr & (0xf << 16)) {
+ pr_notice("Floating-point is not implemented\n");
+ return 0;
+ }
+ elf_hwcap |= HWCAP_FP;
+
+ if (pfr & (0xf << 20))
+ pr_notice("Advanced SIMD is not implemented\n");
+ else
+ elf_hwcap |= HWCAP_ASIMD;
+
+ fpsimd_pm_init();
+
+ return 0;
+}
+late_initcall(fpsimd_init);
Code Review / kvmfornfv.git / blobdiff