[RFC: timer passthrough 5/9] KVM: vmx: use tsc_adjust to enable tsc_offset timer passthrough

[Zhimin Feng]

when in vm:
rdtsc = host_tsc * (TSC multiplier) + tsc_offset(<0)
so when vm write tsc_deadline_msr the value always less than
tsc stampcounter msr value, the irq never be triggered.

the tsc_adjust msr use as below, host execute
rdtsc = host_tsc + tsc_adjust

when vmentry, we set the tsc_adjust equal tsc_offset and vmcs
tsc offset filed equal 0, so the vm execute rdtsc the result like this:
rdtsc = host_tsc + tsc_adjust + 0
the tsc_deadline_msr value will equal tsc stampcounter msr and
the irq will trigger success.

Signed-off-by: Zhimin Feng <fengzhi...@bytedance.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/vmx/vmx.c          | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index be8fc230f7c4..7971c9e755a4 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -534,6 +534,7 @@ struct tick_device {
 struct timer_passth_info {
        u64 host_tscd;
        bool host_in_tscdeadline;
+       u64 host_tsc_adjust;
        struct clock_event_device *curr_dev;
 
        void (*orig_event_handler)(struct clock_event_device *dev);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f824ee46e2d3..44b2fd59587e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6659,6 +6659,27 @@ static fastpath_t vmx_exit_handlers_fastpath(struct 
kvm_vcpu *vcpu)
 
 bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs, bool launched);
 
+static void vmx_adjust_tsc_offset(struct kvm_vcpu *vcpu, bool to_host)
+{
+       u64 tsc_adjust;
+       struct timer_passth_info *local_timer_info;
+
+       local_timer_info = &per_cpu(passth_info, smp_processor_id());
+
+       if (to_host) {
+               tsc_adjust = local_timer_info->host_tsc_adjust;
+               wrmsrl(MSR_IA32_TSC_ADJUST, tsc_adjust);
+               vmcs_write64(TSC_OFFSET, vcpu->arch.tsc_offset);
+       } else {
+               rdmsrl(MSR_IA32_TSC_ADJUST, tsc_adjust);
+               local_timer_info->host_tsc_adjust = tsc_adjust;
+
+               wrmsrl(MSR_IA32_TSC_ADJUST, tsc_adjust + vcpu->arch.tsc_offset);
+               vmcs_write64(TSC_OFFSET, 0);
+
+       }
+}
+
 static void vmx_host_lapic_timer_offload(struct kvm_vcpu *vcpu)
 {
        struct timer_passth_info *local_timer_info;
@@ -6690,6 +6711,7 @@ static void vmx_host_lapic_timer_offload(struct kvm_vcpu 
*vcpu)
                                PIN_BASED_VMX_PREEMPTION_TIMER);
        }
 
+       vmx_adjust_tsc_offset(vcpu, false);
        wrmsrl(MSR_IA32_TSCDEADLINE, 0);
        if (vcpu->arch.tscd > guest_tscl) {
                wrmsrl(MSR_IA32_TSCDEADLINE, vcpu->arch.tscd);
@@ -6711,6 +6733,7 @@ static void vmx_restore_passth_timer(struct kvm_vcpu 
*vcpu)
        u64 guest_tscd;
 
        if (vcpu->arch.timer_passth_enable) {
+               vmx_adjust_tsc_offset(vcpu, true);
                local_timer_info = &per_cpu(passth_info, smp_processor_id());
                host_tscd = local_timer_info->host_tscd;
                rdmsrl(MSR_IA32_TSC_DEADLINE, guest_tscd);
-- 
2.11.0