Re: [PATCH 03/17] Unify vendor TSC logic

[Zachary Amsden <zamsden@redhat.com>]

On 06/15/2010 10:10 PM, Jason Wang wrote:
> Zachary Amsden wrote:
>    
>> Move the TSC control logic from the vendor backends into x86.c
>> by adding adjust_tsc_offset to x86 ops.  Now all TSC decisions
>> can be done in one place.
>>
>> Also, rename some variable in the VCPU structure to more accurately
>> reflect their actual content.
>>
>> VMX backend would record last observed TSC very late (possibly in an
>> IPI to clear the VMCS from a remote CPU), now it is done earlier.
>>
>> Note this is still not yet perfect.  We adjust TSC in both
>> directions when the TSC is unstable, resulting in desynchronized
>> TSCs for SMP guests.  A better choice would be to compensate based
>> on a master reference clock.
>>
>> Signed-off-by: Zachary Amsden<zamsden@redhat.com>
>> ---
>>   arch/x86/include/asm/kvm_host.h |    5 +++--
>>   arch/x86/kvm/svm.c              |   25 +++++++++++--------------
>>   arch/x86/kvm/vmx.c              |   20 ++++++++------------
>>   arch/x86/kvm/x86.c              |   16 +++++++++++-----
>>   4 files changed, 33 insertions(+), 33 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 91631b8..94f6ce8 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -253,7 +253,6 @@ struct kvm_mmu {
>>   };
>>
>>   struct kvm_vcpu_arch {
>> -	u64 host_tsc;
>>   	/*
>>   	 * rip and regs accesses must go through
>>   	 * kvm_{register,rip}_{read,write} functions.
>> @@ -334,9 +333,10 @@ struct kvm_vcpu_arch {
>>
>>   	gpa_t time;
>>   	struct pvclock_vcpu_time_info hv_clock;
>> -	unsigned int hv_clock_tsc_khz;
>> +	unsigned int hw_tsc_khz;
>>   	unsigned int time_offset;
>>   	struct page *time_page;
>> +	u64 last_host_tsc;
>>
>>   	bool nmi_pending;
>>   	bool nmi_injected;
>> @@ -530,6 +530,7 @@ struct kvm_x86_ops {
>>   	u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
>>   	int (*get_lpage_level)(void);
>>   	bool (*rdtscp_supported)(void);
>> +	void (*adjust_tsc_offset)(struct kvm_vcpu *vcpu, s64 adjustment);
>>
>>   	void (*set_supported_cpuid)(u32 func, struct kvm_cpuid_entry2 *entry);
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 09b2145..ee2cf30 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -948,18 +948,6 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>   	int i;
>>
>>   	if (unlikely(cpu != vcpu->cpu)) {
>> -		u64 delta;
>> -
>> -		if (check_tsc_unstable()) {
>> -			/*
>> -			 * Make sure that the guest sees a monotonically
>> -			 * increasing TSC.
>> -			 */
>> -			delta = vcpu->arch.host_tsc - native_read_tsc();
>> -			svm->vmcb->control.tsc_offset += delta;
>> -			if (is_nested(svm))
>> -				svm->nested.hsave->control.tsc_offset += delta;
>> -		}
>>   		svm->asid_generation = 0;
>>   	}
>>
>> @@ -975,8 +963,6 @@ static void svm_vcpu_put(struct kvm_vcpu *vcpu)
>>   	++vcpu->stat.host_state_reload;
>>   	for (i = 0; i<  NR_HOST_SAVE_USER_MSRS; i++)
>>   		wrmsrl(host_save_user_msrs[i], svm->host_user_msrs[i]);
>> -
>> -	vcpu->arch.host_tsc = native_read_tsc();
>>   }
>>
>>   static unsigned long svm_get_rflags(struct kvm_vcpu *vcpu)
>> @@ -3422,6 +3408,15 @@ static bool svm_rdtscp_supported(void)
>>   	return false;
>>   }
>>
>> +static void svm_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment)
>> +{
>> +	struct vcpu_svm *svm = to_svm(vcpu);
>> +
>> +	svm->vmcb->control.tsc_offset += adjustment;
>> +	if (is_nested(svm))
>> +		svm->nested.hsave->control.tsc_offset += adjustment;
>> +}
>> +
>>   static void svm_fpu_deactivate(struct kvm_vcpu *vcpu)
>>   {
>>   	struct vcpu_svm *svm = to_svm(vcpu);
>> @@ -3506,6 +3501,8 @@ static struct kvm_x86_ops svm_x86_ops = {
>>   	.rdtscp_supported = svm_rdtscp_supported,
>>
>>   	.set_supported_cpuid = svm_set_supported_cpuid,
>> +
>> +	.adjust_tsc_offset = svm_adjust_tsc_offset,
>>   };
>>
>>   static int __init svm_init(void)
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index a657e08..a993e67 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -498,7 +498,6 @@ static void __vcpu_clear(void *arg)
>>   		vmcs_clear(vmx->vmcs);
>>   	if (per_cpu(current_vmcs, cpu) == vmx->vmcs)
>>   		per_cpu(current_vmcs, cpu) = NULL;
>> -	rdtscll(vmx->vcpu.arch.host_tsc);
>>   	list_del(&vmx->local_vcpus_link);
>>   	vmx->vcpu.cpu = -1;
>>   	vmx->launched = 0;
>> @@ -881,7 +880,6 @@ static void vmx_load_host_state(struct vcpu_vmx *vmx)
>>   static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>   {
>>   	struct vcpu_vmx *vmx = to_vmx(vcpu);
>> -	u64 tsc_this, delta, new_offset;
>>   	u64 phys_addr = __pa(per_cpu(vmxarea, cpu));
>>
>>   	if (!vmm_exclusive)
>> @@ -914,16 +912,6 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>
>>   		rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp);
>>   		vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
>> -
>> -		/*
>> -		 * Make sure the time stamp counter is monotonous.
>> -		 */
>> -		rdtscll(tsc_this);
>> -		if (tsc_this<  vcpu->arch.host_tsc) {
>> -			delta = vcpu->arch.host_tsc - tsc_this;
>> -			new_offset = vmcs_read64(TSC_OFFSET) + delta;
>> -			vmcs_write64(TSC_OFFSET, new_offset);
>> -		}
>>   	}
>>   }
>>
>> @@ -1153,6 +1141,12 @@ static void guest_write_tsc(u64 guest_tsc, u64 host_tsc)
>>   	vmcs_write64(TSC_OFFSET, guest_tsc - host_tsc);
>>   }
>>
>> +static void vmx_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment)
>> +{
>> +	u64 offset = vmcs_read64(TSC_OFFSET);
>> +	vmcs_write64(TSC_OFFSET, offset + adjustment);
>> +}
>> +
>>   /*
>>    * Reads an msr value (of 'msr_index') into 'pdata'.
>>    * Returns 0 on success, non-0 otherwise.
>> @@ -4340,6 +4334,8 @@ static struct kvm_x86_ops vmx_x86_ops = {
>>   	.rdtscp_supported = vmx_rdtscp_supported,
>>
>>   	.set_supported_cpuid = vmx_set_supported_cpuid,
>> +
>> +	.adjust_tsc_offset = vmx_adjust_tsc_offset,
>>   };
>>
>>   static int __init vmx_init(void)
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 0a102d3..c8289d0 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -929,9 +929,9 @@ static int kvm_write_guest_time(struct kvm_vcpu *v)
>>   		return 1;
>>   	}
>>
>> -	if (unlikely(vcpu->hv_clock_tsc_khz != this_tsc_khz)) {
>> +	if (unlikely(vcpu->hw_tsc_khz != this_tsc_khz)) {
>>   		kvm_set_time_scale(this_tsc_khz,&vcpu->hv_clock);
>> -		vcpu->hv_clock_tsc_khz = this_tsc_khz;
>> +		vcpu->hw_tsc_khz = this_tsc_khz;
>>   	}
>>
>>   	/* Keep irq disabled to prevent changes to the clock */
>> @@ -1805,18 +1805,24 @@ out:
>>
>>   void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>   {
>> +	kvm_x86_ops->vcpu_load(vcpu, cpu);
>>   	if (unlikely(vcpu->cpu != cpu)) {
>> +		/* Make sure TSC doesn't go backwards */
>> +		s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 :
>> +				native_read_tsc() - vcpu->arch.last_host_tsc;
>> +		if (tsc_delta<  0 || check_tsc_unstable())
>>
>>      
> It's better to do the adjustment also when tsc_delta>  0
>    

No, that causes time to stop.