Suleiman Souhlal <suleiman@xxxxxxxxxx> writes:
> This is used to synchronize time between host and guest.
> The guest can request the (guest) physical address it wants the
> data in through the MSR_KVM_TIMEKEEPER_EN MSR.
>
> It currently assumes the host timekeeper is "tsc".
>
> Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 3 +
> arch/x86/include/asm/pvclock-abi.h | 27 ++++++
> arch/x86/include/uapi/asm/kvm_para.h | 1 +
> arch/x86/kvm/x86.c | 121 +++++++++++++++++++++++++++
> 4 files changed, 152 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 50eb430b0ad8..4d622450cb4a 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -659,7 +659,10 @@ struct kvm_vcpu_arch {
> struct pvclock_vcpu_time_info hv_clock;
> unsigned int hw_tsc_khz;
> struct gfn_to_hva_cache pv_time;
> + struct gfn_to_hva_cache pv_timekeeper_g2h;
> + struct pvclock_timekeeper pv_timekeeper;
> bool pv_time_enabled;
> + bool pv_timekeeper_enabled;
> /* set guest stopped flag in pvclock flags field */
> bool pvclock_set_guest_stopped_request;
>
> diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
> index 1436226efe3e..2809008b9b26 100644
> --- a/arch/x86/include/asm/pvclock-abi.h
> +++ b/arch/x86/include/asm/pvclock-abi.h
> @@ -40,6 +40,33 @@ struct pvclock_wall_clock {
> u32 nsec;
> } __attribute__((__packed__));
>
> +struct pvclock_read_base {
> + u64 mask;
> + u64 cycle_last;
> + u32 mult;
> + u32 shift;
> + u64 xtime_nsec;
> + u64 base;
> +} __attribute__((__packed__));
> +
> +struct pvclock_timekeeper {
> + u64 gen;
> + u64 flags;
> + struct pvclock_read_base tkr_mono;
> + struct pvclock_read_base tkr_raw;
> + u64 xtime_sec;
> + u64 ktime_sec;
> + u64 wall_to_monotonic_sec;
> + u64 wall_to_monotonic_nsec;
> + u64 offs_real;
> + u64 offs_boot;
> + u64 offs_tai;
> + u64 raw_sec;
> + u64 tsc_offset;
> +} __attribute__((__packed__));
> +
AFAIU these structures mirror struct tk_read_base and struct timekeeper
but these are intenal to timekeeper so the risk I see is: we decide to
change timekeeper internals and these structures become hard-to-mirror
so I'd think about versioning them from the very beginning, e.g.: host
reports supported timekeer versions in MSR_KVM_TIMEKEEPER_EN (renamed)
and then guest asks for a particular version. This way we can deprecate
old versions eventually.
> +#define PVCLOCK_TIMEKEEPER_ENABLED (1 << 0)
> +
> #define PVCLOCK_TSC_STABLE_BIT (1 << 0)
> #define PVCLOCK_GUEST_STOPPED (1 << 1)
> /* PVCLOCK_COUNTS_FROM_ZERO broke ABI and can't be used anymore. */
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index 2a8e0b6b9805..3ebb1d87db3a 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -50,6 +50,7 @@
> #define MSR_KVM_STEAL_TIME 0x4b564d03
> #define MSR_KVM_PV_EOI_EN 0x4b564d04
> #define MSR_KVM_POLL_CONTROL 0x4b564d05
> +#define MSR_KVM_TIMEKEEPER_EN 0x4b564d06
>
> struct kvm_steal_time {
> __u64 steal;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 661e2bf38526..937f83cdda4b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -157,6 +157,8 @@ module_param(force_emulation_prefix, bool, S_IRUGO);
> int __read_mostly pi_inject_timer = -1;
> module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR);
>
> +static atomic_t pv_timekeepers_nr;
> +
> #define KVM_NR_SHARED_MSRS 16
>
> struct kvm_shared_msrs_global {
> @@ -2729,6 +2731,16 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>
> break;
> }
> + case MSR_KVM_TIMEKEEPER_EN:
> + if (kvm_gfn_to_hva_cache_init(vcpu->kvm,
> + &vcpu->arch.pv_timekeeper_g2h, data,
> + sizeof(struct pvclock_timekeeper)))
> + vcpu->arch.pv_timekeeper_enabled = false;
> + else {
> + vcpu->arch.pv_timekeeper_enabled = true;
> + atomic_inc(&pv_timekeepers_nr);
> + }
> + break;
> case MSR_KVM_ASYNC_PF_EN:
> if (kvm_pv_enable_async_pf(vcpu, data))
> return 1;
> @@ -7097,6 +7109,109 @@ static struct perf_guest_info_callbacks kvm_guest_cbs = {
> };
>
> #ifdef CONFIG_X86_64
> +static DEFINE_SPINLOCK(shadow_pvtk_lock);
> +static struct pvclock_timekeeper shadow_pvtk;
> +
> +static void
> +pvclock_copy_read_base(struct pvclock_read_base *pvtkr,
> + struct tk_read_base *tkr)
> +{
> + pvtkr->cycle_last = tkr->cycle_last;
> + pvtkr->mult = tkr->mult;
> + pvtkr->shift = tkr->shift;
> + pvtkr->mask = tkr->mask;
> + pvtkr->xtime_nsec = tkr->xtime_nsec;
> + pvtkr->base = tkr->base;
> +}
> +
> +static void
> +kvm_copy_into_pvtk(struct kvm_vcpu *vcpu)
> +{
> + struct pvclock_timekeeper *pvtk;
> + unsigned long flags;
> +
> + if (!vcpu->arch.pv_timekeeper_enabled)
> + return;
> +
> + pvtk = &vcpu->arch.pv_timekeeper;
> + if (pvclock_gtod_data.clock.vclock_mode == VCLOCK_TSC) {
> + pvtk->flags |= PVCLOCK_TIMEKEEPER_ENABLED;
> + spin_lock_irqsave(&shadow_pvtk_lock, flags);
> + pvtk->tkr_mono = shadow_pvtk.tkr_mono;
> + pvtk->tkr_raw = shadow_pvtk.tkr_raw;
> +
> + pvtk->xtime_sec = shadow_pvtk.xtime_sec;
> + pvtk->ktime_sec = shadow_pvtk.ktime_sec;
> + pvtk->wall_to_monotonic_sec =
> + shadow_pvtk.wall_to_monotonic_sec;
> + pvtk->wall_to_monotonic_nsec =
> + shadow_pvtk.wall_to_monotonic_nsec;
> + pvtk->offs_real = shadow_pvtk.offs_real;
> + pvtk->offs_boot = shadow_pvtk.offs_boot;
> + pvtk->offs_tai = shadow_pvtk.offs_tai;
> + pvtk->raw_sec = shadow_pvtk.raw_sec;
> + spin_unlock_irqrestore(&shadow_pvtk_lock, flags);
> +
> + pvtk->tsc_offset = kvm_x86_ops->read_l1_tsc_offset(vcpu);
> + } else
> + pvtk->flags &= ~PVCLOCK_TIMEKEEPER_ENABLED;
> +
> + BUILD_BUG_ON(offsetof(struct pvclock_timekeeper, gen) != 0);
> +
> + /*
> + * Make the gen count odd to indicate we are in the process of
> + * updating.
> + */
> + vcpu->arch.pv_timekeeper.gen++;
> + vcpu->arch.pv_timekeeper.gen |= 1;
> +
> + /*
> + * See comment in kvm_guest_time_update() for why we have to do
> + * multiple writes.
> + */
> + kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.pv_timekeeper_g2h,
> + &vcpu->arch.pv_timekeeper, sizeof(vcpu->arch.pv_timekeeper.gen));
> +
> + smp_wmb();
> +
> + kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.pv_timekeeper_g2h,
> + &vcpu->arch.pv_timekeeper, sizeof(vcpu->arch.pv_timekeeper));
> +
> + smp_wmb();
> +
> + vcpu->arch.pv_timekeeper.gen++;
> +
> + kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.pv_timekeeper_g2h,
> + &vcpu->arch.pv_timekeeper, sizeof(vcpu->arch.pv_timekeeper.gen));
> +}
> +
> +static void
> +update_shadow_pvtk(struct timekeeper *tk)
> +{
> + struct pvclock_timekeeper *pvtk;
> + unsigned long flags;
> +
> + pvtk = &shadow_pvtk;
> +
> + if (atomic_read(&pv_timekeepers_nr) == 0 ||
> + pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
> + return;
> +
> + spin_lock_irqsave(&shadow_pvtk_lock, flags);
> + pvclock_copy_read_base(&pvtk->tkr_mono, &tk->tkr_mono);
> + pvclock_copy_read_base(&pvtk->tkr_raw, &tk->tkr_raw);
> +
> + pvtk->xtime_sec = tk->xtime_sec;
> + pvtk->ktime_sec = tk->ktime_sec;
> + pvtk->wall_to_monotonic_sec = tk->wall_to_monotonic.tv_sec;
> + pvtk->wall_to_monotonic_nsec = tk->wall_to_monotonic.tv_nsec;
> + pvtk->offs_real = tk->offs_real;
> + pvtk->offs_boot = tk->offs_boot;
> + pvtk->offs_tai = tk->offs_tai;
> + pvtk->raw_sec = tk->raw_sec;
> + spin_unlock_irqrestore(&shadow_pvtk_lock, flags);
> +}
> +
> static void pvclock_gtod_update_fn(struct work_struct *work)
> {
> struct kvm *kvm;
> @@ -7124,6 +7239,7 @@ static int pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused,
> struct timekeeper *tk = priv;
>
> update_pvclock_gtod(tk);
> + update_shadow_pvtk(tk);
>
> /* disable master clock if host does not trust, or does not
> * use, TSC based clocksource.
> @@ -7940,6 +8056,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>
> bool req_immediate_exit = false;
>
> + kvm_copy_into_pvtk(vcpu);
It doesn't matter for pvclock_gtod_update_fn() but vcpu_enter_guest() is
performance critical. I would suggest to introduce a static key to avoid
this completely when no guest is using this new timekeeper.
> +
> if (kvm_request_pending(vcpu)) {
> if (kvm_check_request(KVM_REQ_GET_VMCS12_PAGES, vcpu))
> kvm_x86_ops->get_vmcs12_pages(vcpu);
> @@ -9020,6 +9138,9 @@ void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
>
> kvmclock_reset(vcpu);
>
> + if (vcpu->arch.pv_timekeeper_enabled)
> + atomic_dec(&pv_timekeepers_nr);
> +
> kvm_x86_ops->vcpu_free(vcpu);
> free_cpumask_var(wbinvd_dirty_mask);
> }
--
Vitaly
