From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>,
Zhimin Feng <fengzhimin@bytedance.com>
Cc: x86@kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, pbonzini@redhat.com,
seanjc@google.com, vkuznets@redhat.com, wanpengli@tencent.com,
jmattson@google.com, joro@8bytes.org, mingo@redhat.com,
bp@alien8.de, hpa@zytor.com, fweisbec@gmail.com,
zhouyibo@bytedance.com, zhanghaozhong@bytedance.com
Subject: Re: [RFC: timer passthrough 5/9] KVM: vmx: use tsc_adjust to enable tsc_offset timer passthrough
Date: Fri, 05 Feb 2021 19:22:24 +0100 [thread overview]
Message-ID: <87blcy8jdr.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <YB09f5oJ+sP9hiy6@hirez.programming.kicks-ass.net>
On Fri, Feb 05 2021 at 13:43, Peter Zijlstra wrote:
> On Fri, Feb 05, 2021 at 06:03:13PM +0800, Zhimin Feng wrote:
>> +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);
>> + }
>> +}
>
> NAK
>
> This wrecks the host TSC value, any host code between this and actually
> entering that VM will observe batshit time.
VMCS TSC offset is there for a reason...
Thanks,
tglx
next prev parent reply other threads:[~2021-02-05 18:27 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-05 10:03 [RESEND RFC: timer passthrough 0/9] Support timer passthrough for VM Zhimin Feng
2021-02-05 10:03 ` [RFC: timer passthrough 1/9] KVM: vmx: hook set_next_event for getting the host tscd Zhimin Feng
2021-02-05 12:28 ` Peter Zijlstra
2021-02-05 18:11 ` Thomas Gleixner
2021-02-23 13:07 ` [External] " Zhimin Feng
2021-02-05 10:03 ` [RFC: timer passthrough 2/9] KVM: vmx: enable host lapic timer offload preemtion timer Zhimin Feng
2021-02-05 10:03 ` [RFC: timer passthrough 3/9] KVM: vmx: enable passthrough timer to guest Zhimin Feng
2021-02-05 10:03 ` [RFC: timer passthrough 4/9] KVM: vmx: enable passth timer switch to sw timer Zhimin Feng
2021-02-05 10:03 ` [RFC: timer passthrough 5/9] KVM: vmx: use tsc_adjust to enable tsc_offset timer passthrough Zhimin Feng
2021-02-05 12:43 ` Peter Zijlstra
2021-02-05 18:22 ` Thomas Gleixner [this message]
2021-02-05 10:03 ` [RFC: timer passthrough 6/9] KVM: vmx: check enable_timer_passth strictly Zhimin Feng
2021-02-05 10:03 ` [RFC: timer passthrough 7/9] KVM: vmx: save the initial value of host tscd Zhimin Feng
2021-02-05 10:03 ` [RFC: timer passthrough 8/9] KVM: vmx: Dynamically open or close the timer-passthrough for pre-vm Zhimin Feng
2021-02-05 10:03 ` [RFC: timer passthrough 9/9] KVM: vmx: query the state of timer-passth for vm Zhimin Feng
2021-02-05 13:34 ` [RESEND RFC: timer passthrough 0/9] Support timer passthrough for VM Paolo Bonzini
2021-02-08 18:13 ` Konrad Rzeszutek Wilk
2021-02-23 13:31 ` [External] " Zhimin Feng
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