Currently, KVM is able to work in 'masterclock' mode passing
PVCLOCK_TSC_STABLE_BIT to guests when the clocksource we use on the host
is TSC. When running nested on Hyper-V we normally use a different one:
TSC page which is resistant to TSC frequency changes on event like L1
migration. Add support for it in KVM.
The only non-trivial change in the patch is in vgettsc(): when updating
our gtod copy we now need to get both the clockread and tsc value.
Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
---
arch/x86/kvm/x86.c | 59 +++++++++++++++++++++++++++++++++++++++---------------
1 file changed, 43 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 34c85aa2e2d1..42063b6d8e48 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -67,6 +67,7 @@
#include <asm/pvclock.h>
#include <asm/div64.h>
#include <asm/irq_remapping.h>
+#include <asm/mshyperv.h>
#define CREATE_TRACE_POINTS
#include "trace.h"
@@ -1374,6 +1375,11 @@ static u64 compute_guest_tsc(struct kvm_vcpu *vcpu, s64
kernel_ns)
return tsc;
}
+static inline int gtod_cs_mode_good(int mode)
+{
+ return mode == VCLOCK_TSC || mode == VCLOCK_HVCLOCK;
+}
+
static void kvm_track_tsc_matching(struct kvm_vcpu *vcpu)
{
#ifdef CONFIG_X86_64
@@ -1393,7 +1399,7 @@ static void kvm_track_tsc_matching(struct kvm_vcpu *vcpu)
* perform request to enable masterclock.
*/
if (ka->use_master_clock ||
- (gtod->clock.vclock_mode == VCLOCK_TSC && vcpus_matched))
+ (gtod_cs_mode_good(gtod->clock.vclock_mode) && vcpus_matched))
kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
trace_kvm_track_tsc(vcpu->vcpu_id, ka->nr_vcpus_matched_tsc,
@@ -1456,6 +1462,19 @@ static void kvm_vcpu_write_tsc_offset(struct kvm_vcpu
*vcpu, u64 offset)
vcpu->arch.tsc_offset = offset;
}
+static inline bool kvm_check_tsc_unstable(void)
+{
+#ifdef CONFIG_X86_64
+ /*
+ * TSC is marked unstable when we're running on Hyper-V,
+ * 'TSC page' clocksource is good.
+ */
+ if (pvclock_gtod_data.clock.vclock_mode == VCLOCK_HVCLOCK)
+ return false;
+#endif
+ return check_tsc_unstable();
+}
+
void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
{
struct kvm *kvm = vcpu->kvm;
@@ -1501,7 +1520,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data
*msr)
*/
if (synchronizing &&
vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) {
- if (!check_tsc_unstable()) {
+ if (!kvm_check_tsc_unstable()) {
offset = kvm->arch.cur_tsc_offset;
pr_debug("kvm: matched tsc offset for %llu\n", data);
} else {
@@ -1606,9 +1625,17 @@ static inline u64 vgettsc(u64 *cycle_now)
long v;
struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
- *cycle_now = read_tsc();
+ if (gtod->clock.vclock_mode == VCLOCK_HVCLOCK) {
+ u64 tsc_pg_val;
+
+ tsc_pg_val = hv_read_tsc_page_tsc(hv_get_tsc_page(), cycle_now);
+ v = (tsc_pg_val - gtod->clock.cycle_last) & gtod->clock.mask;
+ } else {
+ /* VCLOCK_TSC */
+ *cycle_now = read_tsc();
+ v = (*cycle_now - gtod->clock.cycle_last) & gtod->clock.mask;
+ }
- v = (*cycle_now - gtod->clock.cycle_last) & gtod->clock.mask;
return v * gtod->clock.mult;
}
@@ -1654,25 +1681,25 @@ static int do_realtime(struct timespec *ts, u64
*cycle_now)
return mode;
}
-/* returns true if host is using tsc clocksource */
+/* returns true if host is using TSC based clocksource */
static bool kvm_get_time_and_clockread(s64 *kernel_ns, u64 *cycle_now)
{
/* checked again under seqlock below */
- if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
+ if (!gtod_cs_mode_good(pvclock_gtod_data.clock.vclock_mode))
return false;
- return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
+ return gtod_cs_mode_good(do_monotonic_boot(kernel_ns, cycle_now));
}
-/* returns true if host is using tsc clocksource */
+/* returns true if host is using TSC based clocksource */
static bool kvm_get_walltime_and_clockread(struct timespec *ts,
u64 *cycle_now)
{
/* checked again under seqlock below */
- if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
+ if (!gtod_cs_mode_good(pvclock_gtod_data.clock.vclock_mode))
return false;
- return do_realtime(ts, cycle_now) == VCLOCK_TSC;
+ return gtod_cs_mode_good(do_realtime(ts, cycle_now));
}
#endif
@@ -2854,13 +2881,13 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
}
- if (unlikely(vcpu->cpu != cpu) || check_tsc_unstable()) {
+ if (unlikely(vcpu->cpu != cpu) || kvm_check_tsc_unstable()) {
s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 :
rdtsc() - vcpu->arch.last_host_tsc;
if (tsc_delta < 0)
mark_tsc_unstable("KVM discovered backwards TSC");
- if (check_tsc_unstable()) {
+ if (kvm_check_tsc_unstable()) {
u64 offset = kvm_compute_tsc_offset(vcpu,
vcpu->arch.last_guest_tsc);
kvm_vcpu_write_tsc_offset(vcpu, offset);
@@ -6107,9 +6134,9 @@ static int pvclock_gtod_notify(struct notifier_block *nb,
unsigned long unused,
update_pvclock_gtod(tk);
/* disable master clock if host does not trust, or does not
- * use, TSC clocksource
+ * use, TSC based clocksource.
*/
- if (gtod->clock.vclock_mode != VCLOCK_TSC &&
+ if (!gtod_cs_mode_good(gtod->clock.vclock_mode) &&
atomic_read(&kvm_guest_has_master_clock) != 0)
queue_work(system_long_wq, &pvclock_gtod_work);
@@ -7735,7 +7762,7 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
{
struct kvm_vcpu *vcpu;
- if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
+ if (kvm_check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
printk_once(KERN_WARNING
"kvm: SMP vm created on host with unstable TSC; "
"guest TSC will not be reliable\n");
@@ -7889,7 +7916,7 @@ int kvm_arch_hardware_enable(void)
return ret;
local_tsc = rdtsc();
- stable = !check_tsc_unstable();
+ stable = !kvm_check_tsc_unstable();
list_for_each_entry(kvm, &vm_list, vm_list) {
kvm_for_each_vcpu(i, vcpu, kvm) {
if (!stable && vcpu->cpu == smp_processor_id())
--
2.14.3
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