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9977e886cb
linux/arch/s390/kernel/signal.c
Hendrik Brueckner 9977e886cb s390/kernel: lazy restore fpu registers 
Improve the save and restore behavior of FPU register contents to use the
vector extension within the kernel.

The kernel does not use floating-point or vector registers and, therefore,
saving and restoring the FPU register contents are performed for handling
signals or switching processes only.  To prepare for using vector
instructions and vector registers within the kernel, enhance the save
behavior and implement a lazy restore at return to user space from a
system call or interrupt.

To implement the lazy restore, the save_fpu_regs() sets a CPU information
flag, CIF_FPU, to indicate that the FPU registers must be restored.
Saving and setting CIF_FPU is performed in an atomic fashion to be
interrupt-safe.  When the kernel wants to use the vector extension or
wants to change the FPU register state for a task during signal handling,
the save_fpu_regs() must be called first.  The CIF_FPU flag is also set at
process switch.  At return to user space, the FPU state is restored.  In
particular, the FPU state includes the floating-point or vector register
contents, as well as, vector-enablement and floating-point control.  The
FPU state restore and clearing CIF_FPU is also performed in an atomic
fashion.

For KVM, the restore of the FPU register state is performed when restoring
the general-purpose guest registers before the SIE instructions is started.
Because the path towards the SIE instruction is interruptible, the CIF_FPU
flag must be checked again right before going into SIE.  If set, the guest
registers must be reloaded again by re-entering the outer SIE loop.  This
is the same behavior as if the SIE critical section is interrupted.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2015-07-22 09:58:01 +02:00

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/*
* Copyright IBM Corp. 1999, 2006
* Author(s): Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com)
*
* Based on Intel version
*
* Copyright (C) 1991, 1992 Linus Torvalds
*
* 1997-11-28 Modified for POSIX.1b signals by Richard Henderson
*/
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/wait.h>
#include <linux/ptrace.h>
#include <linux/unistd.h>
#include <linux/stddef.h>
#include <linux/tty.h>
#include <linux/personality.h>
#include <linux/binfmts.h>
#include <linux/tracehook.h>
#include <linux/syscalls.h>
#include <linux/compat.h>
#include <asm/ucontext.h>
#include <asm/uaccess.h>
#include <asm/lowcore.h>
#include <asm/switch_to.h>
#include "entry.h"
/*
* Layout of an old-style signal-frame:
* -----------------------------------------
* | save area (_SIGNAL_FRAMESIZE) |
* -----------------------------------------
* | struct sigcontext |
* | oldmask |
* | _sigregs * |
* -----------------------------------------
* | _sigregs with |
* | _s390_regs_common |
* | _s390_fp_regs |
* -----------------------------------------
* | int signo |
* -----------------------------------------
* | _sigregs_ext with |
* | gprs_high 64 byte (opt) |
* | vxrs_low 128 byte (opt) |
* | vxrs_high 256 byte (opt) |
* | reserved 128 byte (opt) |
* -----------------------------------------
* | __u16 svc_insn |
* -----------------------------------------
* The svc_insn entry with the sigreturn system call opcode does not
* have a fixed position and moves if gprs_high or vxrs exist.
* Future extensions will be added to _sigregs_ext.
*/
struct sigframe
{
__u8 callee_used_stack[__SIGNAL_FRAMESIZE];
struct sigcontext sc;
_sigregs sregs;
int signo;
_sigregs_ext sregs_ext;
__u16 svc_insn; /* Offset of svc_insn is NOT fixed! */
};
/*
* Layout of an rt signal-frame:
* -----------------------------------------
* | save area (_SIGNAL_FRAMESIZE) |
* -----------------------------------------
* | svc __NR_rt_sigreturn 2 byte |
* -----------------------------------------
* | struct siginfo |
* -----------------------------------------
* | struct ucontext_extended with |
* | unsigned long uc_flags |
* | struct ucontext *uc_link |
* | stack_t uc_stack |
* | _sigregs uc_mcontext with |
* | _s390_regs_common |
* | _s390_fp_regs |
* | sigset_t uc_sigmask |
* | _sigregs_ext uc_mcontext_ext |
* | gprs_high 64 byte (opt) |
* | vxrs_low 128 byte (opt) |
* | vxrs_high 256 byte (opt)|
* | reserved 128 byte (opt) |
* -----------------------------------------
* Future extensions will be added to _sigregs_ext.
*/
struct rt_sigframe
{
__u8 callee_used_stack[__SIGNAL_FRAMESIZE];
__u16 svc_insn;
struct siginfo info;
struct ucontext_extended uc;
};
/* Store registers needed to create the signal frame */
static void store_sigregs(void)
{
save_access_regs(current->thread.acrs);
save_fpu_regs(&current->thread.fpu);
}
/* Load registers after signal return */
static void load_sigregs(void)
{
restore_access_regs(current->thread.acrs);
}
/* Returns non-zero on fault. */
static int save_sigregs(struct pt_regs *regs, _sigregs __user *sregs)
{
_sigregs user_sregs;
/* Copy a 'clean' PSW mask to the user to avoid leaking
information about whether PER is currently on. */
user_sregs.regs.psw.mask = PSW_USER_BITS |
(regs->psw.mask & (PSW_MASK_USER | PSW_MASK_RI));
user_sregs.regs.psw.addr = regs->psw.addr;
memcpy(&user_sregs.regs.gprs, &regs->gprs, sizeof(sregs->regs.gprs));
memcpy(&user_sregs.regs.acrs, current->thread.acrs,
sizeof(user_sregs.regs.acrs));
fpregs_store(&user_sregs.fpregs, &current->thread.fpu);
if (__copy_to_user(sregs, &user_sregs, sizeof(_sigregs)))
return -EFAULT;
return 0;
}
static int restore_sigregs(struct pt_regs *regs, _sigregs __user *sregs)
{
_sigregs user_sregs;
/* Alwys make any pending restarted system call return -EINTR */
current->restart_block.fn = do_no_restart_syscall;
if (__copy_from_user(&user_sregs, sregs, sizeof(user_sregs)))
return -EFAULT;
if (!is_ri_task(current) && (user_sregs.regs.psw.mask & PSW_MASK_RI))
return -EINVAL;
/* Test the floating-point-control word. */
if (test_fp_ctl(user_sregs.fpregs.fpc))
return -EINVAL;
/* Use regs->psw.mask instead of PSW_USER_BITS to preserve PER bit. */
regs->psw.mask = (regs->psw.mask & ~(PSW_MASK_USER | PSW_MASK_RI)) |
(user_sregs.regs.psw.mask & (PSW_MASK_USER | PSW_MASK_RI));
/* Check for invalid user address space control. */
if ((regs->psw.mask & PSW_MASK_ASC) == PSW_ASC_HOME)
regs->psw.mask = PSW_ASC_PRIMARY |
(regs->psw.mask & ~PSW_MASK_ASC);
/* Check for invalid amode */
if (regs->psw.mask & PSW_MASK_EA)
regs->psw.mask |= PSW_MASK_BA;
regs->psw.addr = user_sregs.regs.psw.addr;
memcpy(&regs->gprs, &user_sregs.regs.gprs, sizeof(sregs->regs.gprs));
memcpy(&current->thread.acrs, &user_sregs.regs.acrs,
sizeof(current->thread.acrs));
fpregs_load(&user_sregs.fpregs, &current->thread.fpu);
clear_pt_regs_flag(regs, PIF_SYSCALL); /* No longer in a system call */
return 0;
}
/* Returns non-zero on fault. */
static int save_sigregs_ext(struct pt_regs *regs,
_sigregs_ext __user *sregs_ext)
{
__u64 vxrs[__NUM_VXRS_LOW];
int i;
/* Save vector registers to signal stack */
if (is_vx_task(current)) {
for (i = 0; i < __NUM_VXRS_LOW; i++)
vxrs[i] = *((__u64 *)(current->thread.fpu.vxrs + i) + 1);
if (__copy_to_user(&sregs_ext->vxrs_low, vxrs,
sizeof(sregs_ext->vxrs_low)) ||
__copy_to_user(&sregs_ext->vxrs_high,
current->thread.fpu.vxrs + __NUM_VXRS_LOW,
sizeof(sregs_ext->vxrs_high)))
return -EFAULT;
}
return 0;
}
static int restore_sigregs_ext(struct pt_regs *regs,
_sigregs_ext __user *sregs_ext)
{
__u64 vxrs[__NUM_VXRS_LOW];
int i;
/* Restore vector registers from signal stack */
if (is_vx_task(current)) {
if (__copy_from_user(vxrs, &sregs_ext->vxrs_low,
sizeof(sregs_ext->vxrs_low)) ||
__copy_from_user(current->thread.fpu.vxrs + __NUM_VXRS_LOW,
&sregs_ext->vxrs_high,
sizeof(sregs_ext->vxrs_high)))
return -EFAULT;
for (i = 0; i < __NUM_VXRS_LOW; i++)
*((__u64 *)(current->thread.fpu.vxrs + i) + 1) = vxrs[i];
}
return 0;
}
SYSCALL_DEFINE0(sigreturn)
{
struct pt_regs *regs = task_pt_regs(current);
struct sigframe __user *frame =
(struct sigframe __user *) regs->gprs[15];
sigset_t set;
if (__copy_from_user(&set.sig, &frame->sc.oldmask, _SIGMASK_COPY_SIZE))
goto badframe;
set_current_blocked(&set);
save_fpu_regs(&current->thread.fpu);
if (restore_sigregs(regs, &frame->sregs))
goto badframe;
if (restore_sigregs_ext(regs, &frame->sregs_ext))
goto badframe;
load_sigregs();
return regs->gprs[2];
badframe:
force_sig(SIGSEGV, current);
return 0;
}
SYSCALL_DEFINE0(rt_sigreturn)
{
struct pt_regs *regs = task_pt_regs(current);
struct rt_sigframe __user *frame =
(struct rt_sigframe __user *)regs->gprs[15];
sigset_t set;
if (__copy_from_user(&set.sig, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;
set_current_blocked(&set);
if (restore_altstack(&frame->uc.uc_stack))
goto badframe;
save_fpu_regs(&current->thread.fpu);
if (restore_sigregs(regs, &frame->uc.uc_mcontext))
goto badframe;
if (restore_sigregs_ext(regs, &frame->uc.uc_mcontext_ext))
goto badframe;
load_sigregs();
return regs->gprs[2];
badframe:
force_sig(SIGSEGV, current);
return 0;
}
/*
* Determine which stack to use..
*/
static inline void __user *
get_sigframe(struct k_sigaction *ka, struct pt_regs * regs, size_t frame_size)
{
unsigned long sp;
/* Default to using normal stack */
sp = regs->gprs[15];
/* Overflow on alternate signal stack gives SIGSEGV. */
if (on_sig_stack(sp) && !on_sig_stack((sp - frame_size) & -8UL))
return (void __user *) -1UL;
/* This is the X/Open sanctioned signal stack switching. */
if (ka->sa.sa_flags & SA_ONSTACK) {
if (! sas_ss_flags(sp))
sp = current->sas_ss_sp + current->sas_ss_size;
}
return (void __user *)((sp - frame_size) & -8ul);
}
static int setup_frame(int sig, struct k_sigaction *ka,
sigset_t *set, struct pt_regs * regs)
{
struct sigframe __user *frame;
struct sigcontext sc;
unsigned long restorer;
size_t frame_size;
/*
* gprs_high are only present for a 31-bit task running on
* a 64-bit kernel (see compat_signal.c) but the space for
* gprs_high need to be allocated if vector registers are
* included in the signal frame on a 31-bit system.
*/
frame_size = sizeof(*frame) - sizeof(frame->sregs_ext);
if (MACHINE_HAS_VX)
frame_size += sizeof(frame->sregs_ext);
frame = get_sigframe(ka, regs, frame_size);
if (frame == (void __user *) -1UL)
return -EFAULT;
/* Set up backchain. */
if (__put_user(regs->gprs[15], (addr_t __user *) frame))
return -EFAULT;
/* Create struct sigcontext on the signal stack */
memcpy(&sc.oldmask, &set->sig, _SIGMASK_COPY_SIZE);
sc.sregs = (_sigregs __user __force *) &frame->sregs;
if (__copy_to_user(&frame->sc, &sc, sizeof(frame->sc)))
return -EFAULT;
/* Store registers needed to create the signal frame */
store_sigregs();
/* Create _sigregs on the signal stack */
if (save_sigregs(regs, &frame->sregs))
return -EFAULT;
/* Place signal number on stack to allow backtrace from handler. */
if (__put_user(regs->gprs[2], (int __user *) &frame->signo))
return -EFAULT;
/* Create _sigregs_ext on the signal stack */
if (save_sigregs_ext(regs, &frame->sregs_ext))
return -EFAULT;
/* Set up to return from userspace. If provided, use a stub
already in userspace. */
if (ka->sa.sa_flags & SA_RESTORER) {
restorer = (unsigned long) ka->sa.sa_restorer | PSW_ADDR_AMODE;
} else {
/* Signal frame without vector registers are short ! */
__u16 __user *svc = (void __user *) frame + frame_size - 2;
if (__put_user(S390_SYSCALL_OPCODE | __NR_sigreturn, svc))
return -EFAULT;
restorer = (unsigned long) svc | PSW_ADDR_AMODE;
}
/* Set up registers for signal handler */
regs->gprs[14] = restorer;
regs->gprs[15] = (unsigned long) frame;
/* Force default amode and default user address space control. */
regs->psw.mask = PSW_MASK_EA | PSW_MASK_BA |
(PSW_USER_BITS & PSW_MASK_ASC) |
(regs->psw.mask & ~PSW_MASK_ASC);
regs->psw.addr = (unsigned long) ka->sa.sa_handler | PSW_ADDR_AMODE;
regs->gprs[2] = sig;
regs->gprs[3] = (unsigned long) &frame->sc;
/* We forgot to include these in the sigcontext.
To avoid breaking binary compatibility, they are passed as args. */
if (sig == SIGSEGV || sig == SIGBUS || sig == SIGILL ||
sig == SIGTRAP || sig == SIGFPE) {
/* set extra registers only for synchronous signals */
regs->gprs[4] = regs->int_code & 127;
regs->gprs[5] = regs->int_parm_long;
regs->gprs[6] = task_thread_info(current)->last_break;
}
return 0;
}
static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
struct pt_regs *regs)
{
struct rt_sigframe __user *frame;
unsigned long uc_flags, restorer;
size_t frame_size;
frame_size = sizeof(struct rt_sigframe) - sizeof(_sigregs_ext);
/*
* gprs_high are only present for a 31-bit task running on
* a 64-bit kernel (see compat_signal.c) but the space for
* gprs_high need to be allocated if vector registers are
* included in the signal frame on a 31-bit system.
*/
uc_flags = 0;
if (MACHINE_HAS_VX) {
frame_size += sizeof(_sigregs_ext);
if (is_vx_task(current))
uc_flags |= UC_VXRS;
}
frame = get_sigframe(&ksig->ka, regs, frame_size);
if (frame == (void __user *) -1UL)
return -EFAULT;
/* Set up backchain. */
if (__put_user(regs->gprs[15], (addr_t __user *) frame))
return -EFAULT;
/* Set up to return from userspace. If provided, use a stub
already in userspace. */
if (ksig->ka.sa.sa_flags & SA_RESTORER) {
restorer = (unsigned long)
ksig->ka.sa.sa_restorer | PSW_ADDR_AMODE;
} else {
__u16 __user *svc = &frame->svc_insn;
if (__put_user(S390_SYSCALL_OPCODE | __NR_rt_sigreturn, svc))
return -EFAULT;
restorer = (unsigned long) svc | PSW_ADDR_AMODE;
}
/* Create siginfo on the signal stack */
if (copy_siginfo_to_user(&frame->info, &ksig->info))
return -EFAULT;
/* Store registers needed to create the signal frame */
store_sigregs();
/* Create ucontext on the signal stack. */
if (__put_user(uc_flags, &frame->uc.uc_flags) ||
__put_user(NULL, &frame->uc.uc_link) ||
__save_altstack(&frame->uc.uc_stack, regs->gprs[15]) ||
save_sigregs(regs, &frame->uc.uc_mcontext) ||
__copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)) ||
save_sigregs_ext(regs, &frame->uc.uc_mcontext_ext))
return -EFAULT;
/* Set up registers for signal handler */
regs->gprs[14] = restorer;
regs->gprs[15] = (unsigned long) frame;
/* Force default amode and default user address space control. */
regs->psw.mask = PSW_MASK_EA | PSW_MASK_BA |
(PSW_USER_BITS & PSW_MASK_ASC) |
(regs->psw.mask & ~PSW_MASK_ASC);
regs->psw.addr = (unsigned long) ksig->ka.sa.sa_handler | PSW_ADDR_AMODE;
regs->gprs[2] = ksig->sig;
regs->gprs[3] = (unsigned long) &frame->info;
regs->gprs[4] = (unsigned long) &frame->uc;
regs->gprs[5] = task_thread_info(current)->last_break;
return 0;
}
static void handle_signal(struct ksignal *ksig, sigset_t *oldset,
struct pt_regs *regs)
{
int ret;
/* Set up the stack frame */
if (ksig->ka.sa.sa_flags & SA_SIGINFO)
ret = setup_rt_frame(ksig, oldset, regs);
else
ret = setup_frame(ksig->sig, &ksig->ka, oldset, regs);
signal_setup_done(ret, ksig, test_thread_flag(TIF_SINGLE_STEP));
}
/*
* Note that 'init' is a special process: it doesn't get signals it doesn't
* want to handle. Thus you cannot kill init even with a SIGKILL even by
* mistake.
*
* Note that we go through the signals twice: once to check the signals that
* the kernel can handle, and then we build all the user-level signal handling
* stack-frames in one go after that.
*/
void do_signal(struct pt_regs *regs)
{
struct ksignal ksig;
sigset_t *oldset = sigmask_to_save();
/*
* Get signal to deliver. When running under ptrace, at this point
* the debugger may change all our registers, including the system
* call information.
*/
current_thread_info()->system_call =
test_pt_regs_flag(regs, PIF_SYSCALL) ? regs->int_code : 0;
if (get_signal(&ksig)) {
/* Whee! Actually deliver the signal. */
if (current_thread_info()->system_call) {
regs->int_code = current_thread_info()->system_call;
/* Check for system call restarting. */
switch (regs->gprs[2]) {
case -ERESTART_RESTARTBLOCK:
case -ERESTARTNOHAND:
regs->gprs[2] = -EINTR;
break;
case -ERESTARTSYS:
if (!(ksig.ka.sa.sa_flags & SA_RESTART)) {
regs->gprs[2] = -EINTR;
break;
}
/* fallthrough */
case -ERESTARTNOINTR:
regs->gprs[2] = regs->orig_gpr2;
regs->psw.addr =
__rewind_psw(regs->psw,
regs->int_code >> 16);
break;
}
}
/* No longer in a system call */
clear_pt_regs_flag(regs, PIF_SYSCALL);
if (is_compat_task())
handle_signal32(&ksig, oldset, regs);
else
handle_signal(&ksig, oldset, regs);
return;
}
/* No handlers present - check for system call restart */
clear_pt_regs_flag(regs, PIF_SYSCALL);
if (current_thread_info()->system_call) {
regs->int_code = current_thread_info()->system_call;
switch (regs->gprs[2]) {
case -ERESTART_RESTARTBLOCK:
/* Restart with sys_restart_syscall */
regs->int_code = __NR_restart_syscall;
/* fallthrough */
case -ERESTARTNOHAND:
case -ERESTARTSYS:
case -ERESTARTNOINTR:
/* Restart system call with magic TIF bit. */
regs->gprs[2] = regs->orig_gpr2;
set_pt_regs_flag(regs, PIF_SYSCALL);
if (test_thread_flag(TIF_SINGLE_STEP))
clear_pt_regs_flag(regs, PIF_PER_TRAP);
break;
}
}
/*
* If there's no signal to deliver, we just put the saved sigmask back.
*/
restore_saved_sigmask();
}
void do_notify_resume(struct pt_regs *regs)
{
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
}
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