/*
* 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/bottom_half.h>
#include <linux/cpu.h>
#include <linux/cpu_pm.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/sched/signal.h>
#include <linux/signal.h>
#include <asm/fpsimd.h>
#include <asm/cputype.h>
#include <asm/simd.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 every time 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.
*
* In order to allow softirq handlers to use FPSIMD, kernel_neon_begin() may
* save the task's FPSIMD context back to task_struct from softirq context.
* To prevent this from racing with the manipulation of the task's FPSIMD state
* from task context and thereby corrupting the state, it is necessary to
* protect any manipulation of a task's fpsimd_state or TIF_FOREIGN_FPSTATE
* flag with local_bh_disable() unless softirqs are already masked.
*
* 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)
{
if (!system_supports_fpsimd())
return;
/*
* 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)
{
if (!system_supports_fpsimd())
return;
local_bh_disable();
memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
fpsimd_flush_task_state(current);
set_thread_flag(TIF_FOREIGN_FPSTATE);
local_bh_enable();
}
/*
* 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)
{
if (!system_supports_fpsimd())
return;
local_bh_disable();
if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
fpsimd_save_state(¤t->thread.fpsimd_state);
local_bh_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)
{
if (!system_supports_fpsimd())
return;
local_bh_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();
}
local_bh_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)
{
if (!system_supports_fpsimd())
return;
local_bh_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();
}
local_bh_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
DEFINE_PER_CPU(bool, kernel_neon_busy);
EXPORT_PER_CPU_SYMBOL(kernel_neon_busy);
/*
* Kernel-side NEON support functions
*/
/*
* kernel_neon_begin(): obtain the CPU FPSIMD registers for use by the calling
* context
*
* Must not be called unless may_use_simd() returns true.
* Task context in the FPSIMD registers is saved back to memory as necessary.
*
* A matching call to kernel_neon_end() must be made before returning from the
* calling context.
*
* The caller may freely use the FPSIMD registers until kernel_neon_end() is
* called.
*/
void kernel_neon_begin(void)
{
if (WARN_ON(!system_supports_fpsimd()))
return;
BUG_ON(!may_use_simd());
local_bh_disable();
__this_cpu_write(kernel_neon_busy, true);
/* Save unsaved task fpsimd state, if any: */
if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
fpsimd_save_state(¤t->thread.fpsimd_state);
/* Invalidate any task state remaining in the fpsimd regs: */
__this_cpu_write(fpsimd_last_state, NULL);
preempt_disable();
local_bh_enable();
}
EXPORT_SYMBOL(kernel_neon_begin);
/*
* kernel_neon_end(): give the CPU FPSIMD registers back to the current task
*
* Must be called from a context in which kernel_neon_begin() was previously
* called, with no call to kernel_neon_end() in the meantime.
*
* The caller must not use the FPSIMD registers after this function is called,
* unless kernel_neon_begin() is called again in the meantime.
*/
void kernel_neon_end(void)
{
bool busy;
if (!system_supports_fpsimd())
return;
busy = __this_cpu_xchg(kernel_neon_busy, false);
WARN_ON(!busy); /* No matching kernel_neon_begin()? */
preempt_enable();
}
EXPORT_SYMBOL(kernel_neon_end);
static DEFINE_PER_CPU(struct fpsimd_state, efi_fpsimd_state);
static DEFINE_PER_CPU(bool, efi_fpsimd_state_used);
/*
* EFI runtime services support functions
*
* The ABI for EFI runtime services allows EFI to use FPSIMD during the call.
* This means that for EFI (and only for EFI), we have to assume that FPSIMD
* is always used rather than being an optional accelerator.
*
* These functions provide the necessary support for ensuring FPSIMD
* save/restore in the contexts from which EFI is used.
*
* Do not use them for any other purpose -- if tempted to do so, you are
* either doing something wrong or you need to propose some refactoring.
*/
/*
* __efi_fpsimd_begin(): prepare FPSIMD for making an EFI runtime services call
*/
void __efi_fpsimd_begin(void)
{
if (!system_supports_fpsimd())
return;
WARN_ON(preemptible());
if (may_use_simd())
kernel_neon_begin();
else {
fpsimd_save_state(this_cpu_ptr(&efi_fpsimd_state));
__this_cpu_write(efi_fpsimd_state_used, true);
}
}
/*
* __efi_fpsimd_end(): clean up FPSIMD after an EFI runtime services call
*/
void __efi_fpsimd_end(void)
{
if (!system_supports_fpsimd())
return;
if (__this_cpu_xchg(efi_fpsimd_state_used, false))
fpsimd_load_state(this_cpu_ptr(&efi_fpsimd_state));
else
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 __init 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 */
#ifdef CONFIG_HOTPLUG_CPU
static int fpsimd_cpu_dead(unsigned int cpu)
{
per_cpu(fpsimd_last_state, cpu) = NULL;
return 0;
}
static inline void fpsimd_hotplug_init(void)
{
cpuhp_setup_state_nocalls(CPUHP_ARM64_FPSIMD_DEAD, "arm64/fpsimd:dead",
NULL, fpsimd_cpu_dead);
}
#else
static inline void fpsimd_hotplug_init(void) { }
#endif
/*
* FP/SIMD support code initialisation.
*/
static int __init fpsimd_init(void)
{
if (elf_hwcap & HWCAP_FP) {
fpsimd_pm_init();
fpsimd_hotplug_init();
} else {
pr_notice("Floating-point is not implemented\n");
}
if (!(elf_hwcap & HWCAP_ASIMD))
pr_notice("Advanced SIMD is not implemented\n");
return 0;
}
late_initcall(fpsimd_init);
