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linux/arch/alpha/include/asm/thread_info.h
Al Viro 0509666660 alpha: lazy FPU switching 
On each context switch we save the FPU registers on stack
of old process and restore FPU registers from the stack of new one.
That allows us to avoid doing that each time we enter/leave the
kernel mode; however, that can get suboptimal in some cases.

	For one thing, we don't need to bother saving anything
for kernel threads.  For another, if between entering and leaving
the kernel a thread gives CPU up more than once, it will do
useless work, saving the same values every time, only to discard
the saved copy as soon as it returns from switch_to().

	Alternative solution:

* move the array we save into from switch_stack to thread_info
* have a (thread-synchronous) flag set when we save them
* have another flag set when they should be restored on return to userland.
* do *NOT* save/restore them in do_switch_stack()/undo_switch_stack().
* restore on the exit to user mode if the restore flag had
been set.  Clear both flags.
* on context switch, entry to fork/clone/vfork, before entry into do_signal()
and on entry into straced syscall save the registers and set the 'saved' flag
unless it had been already set.
* on context switch set the 'restore' flag as well.
* have copy_thread() set both flags for child, so the registers would be
restored once the child returns to userland.
* use the saved data in setup_sigcontext(); have restore_sigcontext() set both flags
and copy from sigframe to save area.
* teach ptrace to look for FPU registers in thread_info instead of
switch_stack.
* teach isolated accesses to FPU registers (rdfpcr, wrfpcr, etc.)
to check the 'saved' flag (under preempt_disable()) and work with the save area
if it's been set; if 'saved' flag is found upon write access, set 'restore' flag
as well.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Matt Turner <mattst88@gmail.com>
2023-02-24 23:14:22 -05:00

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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ALPHA_THREAD_INFO_H
#define _ALPHA_THREAD_INFO_H
#ifdef __KERNEL__
#ifndef __ASSEMBLY__
#include <asm/processor.h>
#include <asm/types.h>
#include <asm/hwrpb.h>
#include <asm/sysinfo.h>
#endif
#ifndef __ASSEMBLY__
struct thread_info {
struct pcb_struct pcb; /* palcode state */
struct task_struct *task; /* main task structure */
unsigned int flags; /* low level flags */
unsigned int ieee_state; /* see fpu.h */
unsigned cpu; /* current CPU */
int preempt_count; /* 0 => preemptable, <0 => BUG */
unsigned int status; /* thread-synchronous flags */
int bpt_nsaved;
unsigned long bpt_addr[2]; /* breakpoint handling */
unsigned int bpt_insn[2];
unsigned long fp[32];
};
/*
* Macros/functions for gaining access to the thread information structure.
*/
#define INIT_THREAD_INFO(tsk) \
{ \
.task = &tsk, \
.preempt_count = INIT_PREEMPT_COUNT, \
}
/* How to get the thread information struct from C. */
register struct thread_info *__current_thread_info __asm__("$8");
#define current_thread_info() __current_thread_info
register unsigned long *current_stack_pointer __asm__ ("$30");
#endif /* __ASSEMBLY__ */
/* Thread information allocation. */
#define THREAD_SIZE_ORDER 1
#define THREAD_SIZE (2*PAGE_SIZE)
/*
* Thread information flags:
* - these are process state flags and used from assembly
* - pending work-to-be-done flags come first and must be assigned to be
* within bits 0 to 7 to fit in and immediate operand.
*
* TIF_SYSCALL_TRACE is known to be 0 via blbs.
*/
#define TIF_SYSCALL_TRACE 0 /* syscall trace active */
#define TIF_NOTIFY_RESUME 1 /* callback before returning to user */
#define TIF_SIGPENDING 2 /* signal pending */
#define TIF_NEED_RESCHED 3 /* rescheduling necessary */
#define TIF_SYSCALL_AUDIT 4 /* syscall audit active */
#define TIF_NOTIFY_SIGNAL 5 /* signal notifications exist */
#define TIF_DIE_IF_KERNEL 9 /* dik recursion lock */
#define TIF_MEMDIE 13 /* is terminating due to OOM killer */
#define TIF_POLLING_NRFLAG 14 /* idle is polling for TIF_NEED_RESCHED */
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
#define _TIF_SIGPENDING (1<<TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
#define _TIF_SYSCALL_AUDIT (1<<TIF_SYSCALL_AUDIT)
#define _TIF_NOTIFY_SIGNAL (1<<TIF_NOTIFY_SIGNAL)
#define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG)
/* Work to do on interrupt/exception return. */
#define _TIF_WORK_MASK (_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
_TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL)
#define TS_UAC_NOPRINT 0x0001 /* ! Preserve the following three */
#define TS_UAC_NOFIX 0x0002 /* ! flags as they match */
#define TS_UAC_SIGBUS 0x0004 /* ! userspace part of 'osf_sysinfo' */
#define TS_SAVED_FP 0x0008
#define TS_RESTORE_FP 0x0010
#define SET_UNALIGN_CTL(task,value) ({ \
__u32 status = task_thread_info(task)->status & ~UAC_BITMASK; \
if (value & PR_UNALIGN_NOPRINT) \
status |= TS_UAC_NOPRINT; \
if (value & PR_UNALIGN_SIGBUS) \
status |= TS_UAC_SIGBUS; \
if (value & 4) /* alpha-specific */ \
status |= TS_UAC_NOFIX; \
task_thread_info(task)->status = status; \
0; })
#define GET_UNALIGN_CTL(task,value) ({ \
__u32 status = task_thread_info(task)->status & ~UAC_BITMASK; \
__u32 res = 0; \
if (status & TS_UAC_NOPRINT) \
res |= PR_UNALIGN_NOPRINT; \
if (status & TS_UAC_SIGBUS) \
res |= PR_UNALIGN_SIGBUS; \
if (status & TS_UAC_NOFIX) \
res |= 4; \
put_user(res, (int __user *)(value)); \
})
#ifndef __ASSEMBLY__
extern void __save_fpu(void);
static inline void save_fpu(void)
{
if (!(current_thread_info()->status & TS_SAVED_FP)) {
current_thread_info()->status |= TS_SAVED_FP;
__save_fpu();
}
}
#endif
#endif /* __KERNEL__ */
#endif /* _ALPHA_THREAD_INFO_H */
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