mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-06 18:16:39 +07:00
73459e2a1a
This reverts commits0a4e6be9ca
and80f7fdb1c7
. The task migration notifier was originally introduced in order to support the pvclock vsyscall with non-synchronized TSC, but KVM only supports it with synchronized TSC. Hence, on KVM the race condition is only needed due to a bad implementation on the host side, and even then it's so rare that it's mostly theoretical. As far as KVM is concerned it's possible to fix the host, avoiding the additional complexity in the vDSO and the (re)introduction of the task migration notifier. Xen, on the other hand, hasn't yet implemented vsyscall support at all, so we do not care about its plans for non-synchronized TSC. Reported-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
167 lines
4.4 KiB
C
167 lines
4.4 KiB
C
/* paravirtual clock -- common code used by kvm/xen
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <linux/kernel.h>
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#include <linux/percpu.h>
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#include <linux/notifier.h>
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#include <linux/sched.h>
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#include <linux/gfp.h>
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#include <linux/bootmem.h>
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#include <asm/fixmap.h>
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#include <asm/pvclock.h>
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static u8 valid_flags __read_mostly = 0;
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void pvclock_set_flags(u8 flags)
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{
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valid_flags = flags;
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}
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unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
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{
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u64 pv_tsc_khz = 1000000ULL << 32;
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do_div(pv_tsc_khz, src->tsc_to_system_mul);
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if (src->tsc_shift < 0)
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pv_tsc_khz <<= -src->tsc_shift;
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else
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pv_tsc_khz >>= src->tsc_shift;
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return pv_tsc_khz;
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}
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void pvclock_touch_watchdogs(void)
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{
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touch_softlockup_watchdog_sync();
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clocksource_touch_watchdog();
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rcu_cpu_stall_reset();
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reset_hung_task_detector();
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}
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static atomic64_t last_value = ATOMIC64_INIT(0);
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void pvclock_resume(void)
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{
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atomic64_set(&last_value, 0);
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}
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u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
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{
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unsigned version;
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cycle_t ret;
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u8 flags;
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do {
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version = __pvclock_read_cycles(src, &ret, &flags);
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} while ((src->version & 1) || version != src->version);
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return flags & valid_flags;
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}
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cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
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{
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unsigned version;
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cycle_t ret;
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u64 last;
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u8 flags;
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do {
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version = __pvclock_read_cycles(src, &ret, &flags);
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} while ((src->version & 1) || version != src->version);
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if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
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src->flags &= ~PVCLOCK_GUEST_STOPPED;
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pvclock_touch_watchdogs();
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}
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if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
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(flags & PVCLOCK_TSC_STABLE_BIT))
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return ret;
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/*
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* Assumption here is that last_value, a global accumulator, always goes
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* forward. If we are less than that, we should not be much smaller.
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* We assume there is an error marging we're inside, and then the correction
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* does not sacrifice accuracy.
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*
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* For reads: global may have changed between test and return,
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* but this means someone else updated poked the clock at a later time.
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* We just need to make sure we are not seeing a backwards event.
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*
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* For updates: last_value = ret is not enough, since two vcpus could be
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* updating at the same time, and one of them could be slightly behind,
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* making the assumption that last_value always go forward fail to hold.
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*/
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last = atomic64_read(&last_value);
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do {
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if (ret < last)
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return last;
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last = atomic64_cmpxchg(&last_value, last, ret);
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} while (unlikely(last != ret));
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return ret;
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}
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void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
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struct pvclock_vcpu_time_info *vcpu_time,
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struct timespec *ts)
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{
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u32 version;
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u64 delta;
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struct timespec now;
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/* get wallclock at system boot */
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do {
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version = wall_clock->version;
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rmb(); /* fetch version before time */
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now.tv_sec = wall_clock->sec;
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now.tv_nsec = wall_clock->nsec;
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rmb(); /* fetch time before checking version */
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} while ((wall_clock->version & 1) || (version != wall_clock->version));
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delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
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delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
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now.tv_nsec = do_div(delta, NSEC_PER_SEC);
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now.tv_sec = delta;
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set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
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}
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#ifdef CONFIG_X86_64
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/*
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* Initialize the generic pvclock vsyscall state. This will allocate
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* a/some page(s) for the per-vcpu pvclock information, set up a
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* fixmap mapping for the page(s)
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*/
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int __init pvclock_init_vsyscall(struct pvclock_vsyscall_time_info *i,
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int size)
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{
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int idx;
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WARN_ON (size != PVCLOCK_VSYSCALL_NR_PAGES*PAGE_SIZE);
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for (idx = 0; idx <= (PVCLOCK_FIXMAP_END-PVCLOCK_FIXMAP_BEGIN); idx++) {
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__set_fixmap(PVCLOCK_FIXMAP_BEGIN + idx,
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__pa(i) + (idx*PAGE_SIZE),
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PAGE_KERNEL_VVAR);
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}
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return 0;
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}
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#endif
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