From: Marcelo Tosatti Date: Mon, 28 Oct 2019 14:36:22 +0000 (-0200) Subject: KVM: x86: switch KVMCLOCK base to monotonic raw clock X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=53fafdbb8b21f;p=openwrt%2Fstaging%2Fblogic.git KVM: x86: switch KVMCLOCK base to monotonic raw clock Commit 0bc48bea36d1 ("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 Signed-off-by: Marcelo Tosatti Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 19a0dc96beca..89621025577a 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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(>od->seq); - ns = gtod->nsec_base; - ns += vgettsc(tsc_timestamp, &mode); + ns = gtod->monotonic_raw_nsec; + ns += vgettsc(>od->raw_clock, tsc_timestamp, &mode); ns >>= gtod->clock.shift; - ns += gtod->boot_ns; + ns += gtod->boot_ns_raw; } while (unlikely(read_seqcount_retry(>od->seq, seq))); *t = ns; @@ -2054,7 +2069,7 @@ static int do_realtime(struct timespec64 *ts, u64 *tsc_timestamp) seq = read_seqcount_begin(>od->seq); ts->tv_sec = gtod->wall_time_sec; ns = gtod->nsec_base; - ns += vgettsc(tsc_timestamp, &mode); + ns += vgettsc(>od->clock, tsc_timestamp, &mode); ns >>= gtod->clock.shift; } while (unlikely(read_seqcount_retry(>od->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)); }