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linux/arch/s390/include/asm/entry-common.h
Heiko Carstens 8c09871a95 s390/fpu: limit save and restore to used registers
The first invocation of kernel_fpu_begin() after switching from user to
kernel context will save all vector registers, even if only parts of the
vector registers are used within the kernel fpu context. Given that save
and restore of all vector registers is quite expensive change the current
approach in several ways:

- Instead of saving and restoring all user registers limit this to those
  registers which are actually used within an kernel fpu context.

- On context switch save all remaining user fpu registers, so they can be
  restored when the task is rescheduled.

- Saving user registers within kernel_fpu_begin() is done without disabling
  and enabling interrupts - which also slightly reduces runtime. In worst
  case (e.g. interrupt context uses the same registers) this may lead to
  the situation that registers are saved several times, however the
  assumption is that this will not happen frequently, so that the new
  method is faster in nearly all cases.

- save_user_fpu_regs() can still be called from all contexts and saves all
  (or all remaining) user registers to a tasks ufpu user fpu save area.

Overall this reduces the time required to save and restore the user fpu
context for nearly all cases.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
2024-02-16 14:30:16 +01:00

63 lines
1.4 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef ARCH_S390_ENTRY_COMMON_H
#define ARCH_S390_ENTRY_COMMON_H
#include <linux/sched.h>
#include <linux/audit.h>
#include <linux/randomize_kstack.h>
#include <linux/processor.h>
#include <linux/uaccess.h>
#include <asm/timex.h>
#include <asm/fpu.h>
#include <asm/pai.h>
#define ARCH_EXIT_TO_USER_MODE_WORK (_TIF_GUARDED_STORAGE | _TIF_PER_TRAP)
void do_per_trap(struct pt_regs *regs);
static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs)
{
if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
debug_user_asce(0);
pai_kernel_enter(regs);
}
#define arch_enter_from_user_mode arch_enter_from_user_mode
static __always_inline void arch_exit_to_user_mode_work(struct pt_regs *regs,
unsigned long ti_work)
{
if (ti_work & _TIF_PER_TRAP) {
clear_thread_flag(TIF_PER_TRAP);
do_per_trap(regs);
}
if (ti_work & _TIF_GUARDED_STORAGE)
gs_load_bc_cb(regs);
}
#define arch_exit_to_user_mode_work arch_exit_to_user_mode_work
static __always_inline void arch_exit_to_user_mode(void)
{
load_user_fpu_regs();
if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
debug_user_asce(1);
pai_kernel_exit(current_pt_regs());
}
#define arch_exit_to_user_mode arch_exit_to_user_mode
static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
unsigned long ti_work)
{
choose_random_kstack_offset(get_tod_clock_fast() & 0xff);
}
#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
#endif