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KVM: x86: switch KVMCLOCK base to monotonic raw clock

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Commit 0bc48bea36 ("KVM: x86: update master clock before computing
kvmclock_offset")
switches the order of operations to avoid the conversion

TSC (without frequency correction) ->
system_timestamp (with frequency correction),

which might cause a time jump.

However, it leaves any other masterclock update unsafe, which includes,
at the moment:

        * HV_X64_MSR_REFERENCE_TSC MSR write.
        * TSC writes.
        * Host suspend/resume.

Avoid the time jump issue by using frequency uncorrected
CLOCK_MONOTONIC_RAW clock.

Its the guests time keeping software responsability
to track and correct a reference clock such as UTC.

This fixes forward time jump (which can result in
failure to bring up a vCPU) during vCPU hotplug:

Oct 11 14:48:33 storage kernel: CPU2 has been hot-added
Oct 11 14:48:34 storage kernel: CPU3 has been hot-added
Oct 11 14:49:22 storage kernel: smpboot: Booting Node 0 Processor 2 APIC 0x2          <-- time jump of almost 1 minute
Oct 11 14:49:22 storage kernel: smpboot: do_boot_cpu failed(-1) to wakeup CPU#2
Oct 11 14:49:23 storage kernel: smpboot: Booting Node 0 Processor 3 APIC 0x3
Oct 11 14:49:23 storage kernel: kvm-clock: cpu 3, msr 0:7ff640c1, secondary cpu clock

Which happens because:

                /*
                 * Wait 10s total for a response from AP
                 */
                boot_error = -1;
                timeout = jiffies + 10*HZ;
                while (time_before(jiffies, timeout)) {
                         ...
                }

Analyzed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Marcelo Tosatti 2019-10-28 12:36:22 -02:00 committed by Paolo Bonzini
parent e7011c5d17
commit 53fafdbb8b
1 changed files with 37 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

59
arch/x86/kvm/x86.c
View File

@ -1526,20 +1526,25 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
}
#ifdef CONFIG_X86_64
struct pvclock_clock {
int vclock_mode;
u64 cycle_last;
u64 mask;
u32 mult;
u32 shift;
};
struct pvclock_gtod_data {
seqcount_t seq;
struct { /* extract of a clocksource struct */
int vclock_mode;
u64 cycle_last;
u64 mask;
u32 mult;
u32 shift;
} clock;
struct pvclock_clock clock; /* extract of a clocksource struct */
struct pvclock_clock raw_clock; /* extract of a clocksource struct */
u64 boot_ns_raw;
u64 boot_ns;
u64 nsec_base;
u64 wall_time_sec;
u64 monotonic_raw_nsec;
};
static struct pvclock_gtod_data pvclock_gtod_data;
@ -1547,9 +1552,10 @@ static struct pvclock_gtod_data pvclock_gtod_data;
static void update_pvclock_gtod(struct timekeeper *tk)
{
struct pvclock_gtod_data *vdata = &pvclock_gtod_data;
u64 boot_ns;
u64 boot_ns, boot_ns_raw;
boot_ns = ktime_to_ns(ktime_add(tk->tkr_mono.base, tk->offs_boot));
boot_ns_raw = ktime_to_ns(ktime_add(tk->tkr_raw.base, tk->offs_boot));
write_seqcount_begin(&vdata->seq);
@ -1560,11 +1566,20 @@ static void update_pvclock_gtod(struct timekeeper *tk)
vdata->clock.mult = tk->tkr_mono.mult;
vdata->clock.shift = tk->tkr_mono.shift;
vdata->raw_clock.vclock_mode = tk->tkr_raw.clock->archdata.vclock_mode;
vdata->raw_clock.cycle_last = tk->tkr_raw.cycle_last;
vdata->raw_clock.mask = tk->tkr_raw.mask;
vdata->raw_clock.mult = tk->tkr_raw.mult;
vdata->raw_clock.shift = tk->tkr_raw.shift;
vdata->boot_ns = boot_ns;
vdata->nsec_base = tk->tkr_mono.xtime_nsec;
vdata->wall_time_sec = tk->xtime_sec;
vdata->boot_ns_raw = boot_ns_raw;
vdata->monotonic_raw_nsec = tk->tkr_raw.xtime_nsec;
write_seqcount_end(&vdata->seq);
}
#endif
@ -1988,21 +2003,21 @@ static u64 read_tsc(void)
return last;
}
static inline u64 vgettsc(u64 *tsc_timestamp, int *mode)
static inline u64 vgettsc(struct pvclock_clock *clock, u64 *tsc_timestamp,
int *mode)
{
long v;
struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
u64 tsc_pg_val;
switch (gtod->clock.vclock_mode) {
switch (clock->vclock_mode) {
case VCLOCK_HVCLOCK:
tsc_pg_val = hv_read_tsc_page_tsc(hv_get_tsc_page(),
tsc_timestamp);
if (tsc_pg_val != U64_MAX) {
/* TSC page valid */
*mode = VCLOCK_HVCLOCK;
v = (tsc_pg_val - gtod->clock.cycle_last) &
gtod->clock.mask;
v = (tsc_pg_val - clock->cycle_last) &
clock->mask;
} else {
/* TSC page invalid */
*mode = VCLOCK_NONE;
@ -2011,8 +2026,8 @@ static inline u64 vgettsc(u64 *tsc_timestamp, int *mode)
case VCLOCK_TSC:
*mode = VCLOCK_TSC;
*tsc_timestamp = read_tsc();
v = (*tsc_timestamp - gtod->clock.cycle_last) &
gtod->clock.mask;
v = (*tsc_timestamp - clock->cycle_last) &
clock->mask;
break;
default:
*mode = VCLOCK_NONE;
@ -2021,10 +2036,10 @@ static inline u64 vgettsc(u64 *tsc_timestamp, int *mode)
if (*mode == VCLOCK_NONE)
*tsc_timestamp = v = 0;
return v * gtod->clock.mult;
return v * clock->mult;
}
static int do_monotonic_boot(s64 *t, u64 *tsc_timestamp)
static int do_monotonic_raw(s64 *t, u64 *tsc_timestamp)
{
struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
unsigned long seq;
@ -2033,10 +2048,10 @@ static int do_monotonic_boot(s64 *t, u64 *tsc_timestamp)
do {
seq = read_seqcount_begin(&gtod->seq);
ns = gtod->nsec_base;
ns += vgettsc(tsc_timestamp, &mode);
ns = gtod->monotonic_raw_nsec;
ns += vgettsc(&gtod->raw_clock, tsc_timestamp, &mode);
ns >>= gtod->clock.shift;
ns += gtod->boot_ns;
ns += gtod->boot_ns_raw;
} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
*t = ns;
@ -2054,7 +2069,7 @@ static int do_realtime(struct timespec64 *ts, u64 *tsc_timestamp)
seq = read_seqcount_begin(&gtod->seq);
ts->tv_sec = gtod->wall_time_sec;
ns = gtod->nsec_base;
ns += vgettsc(tsc_timestamp, &mode);
ns += vgettsc(&gtod->clock, tsc_timestamp, &mode);
ns >>= gtod->clock.shift;
} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
@ -2071,7 +2086,7 @@ static bool kvm_get_time_and_clockread(s64 *kernel_ns, u64 *tsc_timestamp)
if (!gtod_is_based_on_tsc(pvclock_gtod_data.clock.vclock_mode))
return false;
return gtod_is_based_on_tsc(do_monotonic_boot(kernel_ns,
return gtod_is_based_on_tsc(do_monotonic_raw(kernel_ns,
tsc_timestamp));
}