Re: [v2 PATCH 4/4] x86/kvm: Add guest side support for virtual suspend time injection
From: Thomas Gleixner <hidden>
Date: 2021-08-10 15:48:12
Also in:
lkml
On Fri, Aug 06 2021 at 19:07, Hikaru Nishida wrote:
arch/x86/Kconfig | 13 ++++++++++ arch/x86/include/asm/idtentry.h | 4 +++ arch/x86/include/asm/kvm_para.h | 9 +++++++ arch/x86/kernel/kvmclock.c | 40 +++++++++++++++++++++++++++++ include/linux/timekeeper_internal.h | 4 +++ kernel/time/timekeeping.c | 33 ++++++++++++++++++++++++
Again, this wants to be split into infrastructure and usage.
quoted hunk ↗ jump to hunk
--- a/include/linux/timekeeper_internal.h +++ b/include/linux/timekeeper_internal.h@@ -124,6 +124,10 @@ struct timekeeper {u32 ntp_err_mult; /* Flag used to avoid updating NTP twice with same second */ u32 skip_second_overflow; +#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING_GUEST + /* suspend_time_injected keeps the duration injected through kvm */ + u64 suspend_time_injected;
This is KVM only, so please can we have a name for that struct member which reflects this?
+#endif #ifdef CONFIG_DEBUG_TIMEKEEPING long last_warning; /*
quoted hunk ↗ jump to hunk
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 3ac3fb479981..424c61d38646 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c@@ -2125,6 +2125,39 @@ static u64 logarithmic_accumulation(struct timekeeper *tk, u64 offset, return offset; } +#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING_GUEST +/* + * timekeeping_inject_virtual_suspend_time - Inject virtual suspend time + * when requested by the kvm host.
If this is an attempt to provide a kernel-doc comment for this function, then it's clearly a failed attempt and aside of that malformatted.
+ * This function should be called under irq context.
Why? There is no reason for being called from interrupt context and nothing inforces it.
+ */
+void timekeeping_inject_virtual_suspend_time(void)
+{
+ /*
+ * Only updates shadow_timekeeper so the change will be reflected
+ * on the next call of timekeeping_advance().
No. That's broken.
timekeeping_inject_virtual_suspend_time();
do_settimeofday() or do_adjtimex()
timekeeping_update(tk, TK_MIRROR...);
and your change to the shadow timekeeper is gone.
Of course there is also no justification for this approach. What's wrong
with updating it right away?
+ */ + struct timekeeper *tk = &shadow_timekeeper; + unsigned long flags; + struct timespec64 delta; + u64 suspend_time;
Please sort variables in reverse fir tree order and not randomly as you see fit.
+
+ raw_spin_lock_irqsave(&timekeeper_lock, flags);
+ suspend_time = kvm_get_suspend_time();
+ if (suspend_time > tk->suspend_time_injected) {
+ /*
+ * Do injection only if the time is not injected yet.
+ * suspend_time and tk->suspend_time_injected values are
+ * cummrative, so take a diff and inject the duration.cummrative?
+ */ + delta = ns_to_timespec64(suspend_time - tk->suspend_time_injected); + __timekeeping_inject_sleeptime(tk, &delta); + tk->suspend_time_injected = suspend_time;
It's absolutely unclear how this storage and diff magic works and the
comment is not helping someone not familiar with the implementation of
kvm_get_suspend_time() and the related code at all. Please explain
non-obvious logic properly.
Thanks,
tglx