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linux_dsm_epyc7002/arch/arm64/kernel/vdso/gettimeofday.S
Will Deacon 75a19a0202 arm64: arch_timer: Ensure counter register reads occur with seqlock held 
When executing clock_gettime(), either in the vDSO or via a system call,
we need to ensure that the read of the counter register occurs within
the seqlock reader critical section. This ensures that updates to the
clocksource parameters (e.g. the multiplier) are consistent with the
counter value and therefore avoids the situation where time appears to
go backwards across multiple reads.

Extend the vDSO logic so that the seqlock critical section covers the
read of the counter register as well as accesses to the data page. Since
reads of the counter system registers are not ordered by memory barrier
instructions, introduce dependency ordering from the counter read to a
subsequent memory access so that the seqlock memory barriers apply to
the counter access in both the vDSO and the system call paths.

Cc: <stable@vger.kernel.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/linux-arm-kernel/alpine.DEB.2.21.1902081950260.1662@nanos.tec.linutronix.de/
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Will Deacon <will.deacon@arm.com>
2019-04-30 11:04:23 +01:00

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/*
* Userspace implementations of gettimeofday() and friends.
*
* Copyright (C) 2012 ARM Limited
*
* 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/>.
*
* Author: Will Deacon <will.deacon@arm.com>
*/
#include <linux/linkage.h>
#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#define NSEC_PER_SEC_LO16 0xca00
#define NSEC_PER_SEC_HI16 0x3b9a
vdso_data .req x6
seqcnt .req w7
w_tmp .req w8
x_tmp .req x8
/*
* Conventions for macro arguments:
* - An argument is write-only if its name starts with "res".
* - All other arguments are read-only, unless otherwise specified.
*/
.macro seqcnt_acquire
9999: ldr seqcnt, [vdso_data, #VDSO_TB_SEQ_COUNT]
tbnz seqcnt, #0, 9999b
dmb ishld
.endm
.macro seqcnt_check fail
dmb ishld
ldr w_tmp, [vdso_data, #VDSO_TB_SEQ_COUNT]
cmp w_tmp, seqcnt
b.ne \fail
.endm
.macro syscall_check fail
ldr w_tmp, [vdso_data, #VDSO_USE_SYSCALL]
cbnz w_tmp, \fail
.endm
.macro get_nsec_per_sec res
mov \res, #NSEC_PER_SEC_LO16
movk \res, #NSEC_PER_SEC_HI16, lsl #16
.endm
/*
* Returns the clock delta, in nanoseconds left-shifted by the clock
* shift.
*/
.macro get_clock_shifted_nsec res, cycle_last, mult
/* Read the virtual counter. */
isb
mrs x_tmp, cntvct_el0
/* Calculate cycle delta and convert to ns. */
sub \res, x_tmp, \cycle_last
/* We can only guarantee 56 bits of precision. */
movn x_tmp, #0xff00, lsl #48
and \res, x_tmp, \res
mul \res, \res, \mult
/*
* Fake address dependency from the value computed from the counter
* register to subsequent data page accesses so that the sequence
* locking also orders the read of the counter.
*/
and x_tmp, \res, xzr
add vdso_data, vdso_data, x_tmp
.endm
/*
* Returns in res_{sec,nsec} the REALTIME timespec, based on the
* "wall time" (xtime) and the clock_mono delta.
*/
.macro get_ts_realtime res_sec, res_nsec, \
clock_nsec, xtime_sec, xtime_nsec, nsec_to_sec
add \res_nsec, \clock_nsec, \xtime_nsec
udiv x_tmp, \res_nsec, \nsec_to_sec
add \res_sec, \xtime_sec, x_tmp
msub \res_nsec, x_tmp, \nsec_to_sec, \res_nsec
.endm
/*
* Returns in res_{sec,nsec} the timespec based on the clock_raw delta,
* used for CLOCK_MONOTONIC_RAW.
*/
.macro get_ts_clock_raw res_sec, res_nsec, clock_nsec, nsec_to_sec
udiv \res_sec, \clock_nsec, \nsec_to_sec
msub \res_nsec, \res_sec, \nsec_to_sec, \clock_nsec
.endm
/* sec and nsec are modified in place. */
.macro add_ts sec, nsec, ts_sec, ts_nsec, nsec_to_sec
/* Add timespec. */
add \sec, \sec, \ts_sec
add \nsec, \nsec, \ts_nsec
/* Normalise the new timespec. */
cmp \nsec, \nsec_to_sec
b.lt 9999f
sub \nsec, \nsec, \nsec_to_sec
add \sec, \sec, #1
9999:
cmp \nsec, #0
b.ge 9998f
add \nsec, \nsec, \nsec_to_sec
sub \sec, \sec, #1
9998:
.endm
.macro clock_gettime_return, shift=0
.if \shift == 1
lsr x11, x11, x12
.endif
stp x10, x11, [x1, #TSPEC_TV_SEC]
mov x0, xzr
ret
.endm
.macro jump_slot jumptable, index, label
.if (. - \jumptable) != 4 * (\index)
.error "Jump slot index mismatch"
.endif
b \label
.endm
.text
/* int __kernel_gettimeofday(struct timeval *tv, struct timezone *tz); */
ENTRY(__kernel_gettimeofday)
.cfi_startproc
adr vdso_data, _vdso_data
/* If tv is NULL, skip to the timezone code. */
cbz x0, 2f
/* Compute the time of day. */
1: seqcnt_acquire
syscall_check fail=4f
ldr x10, [vdso_data, #VDSO_CS_CYCLE_LAST]
/* w11 = cs_mono_mult, w12 = cs_shift */
ldp w11, w12, [vdso_data, #VDSO_CS_MONO_MULT]
ldp x13, x14, [vdso_data, #VDSO_XTIME_CLK_SEC]
get_nsec_per_sec res=x9
lsl x9, x9, x12
get_clock_shifted_nsec res=x15, cycle_last=x10, mult=x11
seqcnt_check fail=1b
get_ts_realtime res_sec=x10, res_nsec=x11, \
clock_nsec=x15, xtime_sec=x13, xtime_nsec=x14, nsec_to_sec=x9
/* Convert ns to us. */
mov x13, #1000
lsl x13, x13, x12
udiv x11, x11, x13
stp x10, x11, [x0, #TVAL_TV_SEC]
2:
/* If tz is NULL, return 0. */
cbz x1, 3f
ldp w4, w5, [vdso_data, #VDSO_TZ_MINWEST]
stp w4, w5, [x1, #TZ_MINWEST]
3:
mov x0, xzr
ret
4:
/* Syscall fallback. */
mov x8, #__NR_gettimeofday
svc #0
ret
.cfi_endproc
ENDPROC(__kernel_gettimeofday)
#define JUMPSLOT_MAX CLOCK_MONOTONIC_COARSE
/* int __kernel_clock_gettime(clockid_t clock_id, struct timespec *tp); */
ENTRY(__kernel_clock_gettime)
.cfi_startproc
cmp w0, #JUMPSLOT_MAX
b.hi syscall
adr vdso_data, _vdso_data
adr x_tmp, jumptable
add x_tmp, x_tmp, w0, uxtw #2
br x_tmp
ALIGN
jumptable:
jump_slot jumptable, CLOCK_REALTIME, realtime
jump_slot jumptable, CLOCK_MONOTONIC, monotonic
b syscall
b syscall
jump_slot jumptable, CLOCK_MONOTONIC_RAW, monotonic_raw
jump_slot jumptable, CLOCK_REALTIME_COARSE, realtime_coarse
jump_slot jumptable, CLOCK_MONOTONIC_COARSE, monotonic_coarse
.if (. - jumptable) != 4 * (JUMPSLOT_MAX + 1)
.error "Wrong jumptable size"
.endif
ALIGN
realtime:
seqcnt_acquire
syscall_check fail=syscall
ldr x10, [vdso_data, #VDSO_CS_CYCLE_LAST]
/* w11 = cs_mono_mult, w12 = cs_shift */
ldp w11, w12, [vdso_data, #VDSO_CS_MONO_MULT]
ldp x13, x14, [vdso_data, #VDSO_XTIME_CLK_SEC]
/* All computations are done with left-shifted nsecs. */
get_nsec_per_sec res=x9
lsl x9, x9, x12
get_clock_shifted_nsec res=x15, cycle_last=x10, mult=x11
seqcnt_check fail=realtime
get_ts_realtime res_sec=x10, res_nsec=x11, \
clock_nsec=x15, xtime_sec=x13, xtime_nsec=x14, nsec_to_sec=x9
clock_gettime_return, shift=1
ALIGN
monotonic:
seqcnt_acquire
syscall_check fail=syscall
ldr x10, [vdso_data, #VDSO_CS_CYCLE_LAST]
/* w11 = cs_mono_mult, w12 = cs_shift */
ldp w11, w12, [vdso_data, #VDSO_CS_MONO_MULT]
ldp x13, x14, [vdso_data, #VDSO_XTIME_CLK_SEC]
ldp x3, x4, [vdso_data, #VDSO_WTM_CLK_SEC]
/* All computations are done with left-shifted nsecs. */
lsl x4, x4, x12
get_nsec_per_sec res=x9
lsl x9, x9, x12
get_clock_shifted_nsec res=x15, cycle_last=x10, mult=x11
seqcnt_check fail=monotonic
get_ts_realtime res_sec=x10, res_nsec=x11, \
clock_nsec=x15, xtime_sec=x13, xtime_nsec=x14, nsec_to_sec=x9
add_ts sec=x10, nsec=x11, ts_sec=x3, ts_nsec=x4, nsec_to_sec=x9
clock_gettime_return, shift=1
ALIGN
monotonic_raw:
seqcnt_acquire
syscall_check fail=syscall
ldr x10, [vdso_data, #VDSO_CS_CYCLE_LAST]
/* w11 = cs_raw_mult, w12 = cs_shift */
ldp w12, w11, [vdso_data, #VDSO_CS_SHIFT]
ldp x13, x14, [vdso_data, #VDSO_RAW_TIME_SEC]
/* All computations are done with left-shifted nsecs. */
get_nsec_per_sec res=x9
lsl x9, x9, x12
get_clock_shifted_nsec res=x15, cycle_last=x10, mult=x11
seqcnt_check fail=monotonic_raw
get_ts_clock_raw res_sec=x10, res_nsec=x11, \
clock_nsec=x15, nsec_to_sec=x9
add_ts sec=x10, nsec=x11, ts_sec=x13, ts_nsec=x14, nsec_to_sec=x9
clock_gettime_return, shift=1
ALIGN
realtime_coarse:
seqcnt_acquire
ldp x10, x11, [vdso_data, #VDSO_XTIME_CRS_SEC]
seqcnt_check fail=realtime_coarse
clock_gettime_return
ALIGN
monotonic_coarse:
seqcnt_acquire
ldp x10, x11, [vdso_data, #VDSO_XTIME_CRS_SEC]
ldp x13, x14, [vdso_data, #VDSO_WTM_CLK_SEC]
seqcnt_check fail=monotonic_coarse
/* Computations are done in (non-shifted) nsecs. */
get_nsec_per_sec res=x9
add_ts sec=x10, nsec=x11, ts_sec=x13, ts_nsec=x14, nsec_to_sec=x9
clock_gettime_return
ALIGN
syscall: /* Syscall fallback. */
mov x8, #__NR_clock_gettime
svc #0
ret
.cfi_endproc
ENDPROC(__kernel_clock_gettime)
/* int __kernel_clock_getres(clockid_t clock_id, struct timespec *res); */
ENTRY(__kernel_clock_getres)
.cfi_startproc
cmp w0, #CLOCK_REALTIME
ccmp w0, #CLOCK_MONOTONIC, #0x4, ne
ccmp w0, #CLOCK_MONOTONIC_RAW, #0x4, ne
b.ne 1f
adr vdso_data, _vdso_data
ldr w2, [vdso_data, #CLOCK_REALTIME_RES]
b 2f
1:
cmp w0, #CLOCK_REALTIME_COARSE
ccmp w0, #CLOCK_MONOTONIC_COARSE, #0x4, ne
b.ne 4f
ldr x2, 5f
2:
cbz x1, 3f
stp xzr, x2, [x1]
3: /* res == NULL. */
mov w0, wzr
ret
4: /* Syscall fallback. */
mov x8, #__NR_clock_getres
svc #0
ret
5:
.quad CLOCK_COARSE_RES
.cfi_endproc
ENDPROC(__kernel_clock_getres)
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