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From: Paolo Bonzini <pbonzini@redhat.com>
To: Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc: Oliver Upton <oupton@google.com>, Ingo Molnar <mingo@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	open list <linux-kernel@vger.kernel.org>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Wanpeng Li <wanpengli@tencent.com>,
	Borislav Petkov <bp@alien8.de>, Jim Mattson <jmattson@google.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Joerg Roedel <joro@8bytes.org>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH 1/2] KVM: x86: implement KVM_SET_TSC_PRECISE/KVM_GET_TSC_PRECISE
Date: Mon, 30 Nov 2020 15:33:46 +0100	[thread overview]
Message-ID: <38602ef4-7ecf-a5fd-6db9-db86e8e974e4@redhat.com> (raw)
In-Reply-To: <20201130133559.233242-2-mlevitsk@redhat.com>

On 30/11/20 14:35, Maxim Levitsky wrote:
> +		if (guest_cpuid_has(vcpu, X86_FEATURE_TSC_ADJUST)) {
> +			tsc_state.tsc_adjust = vcpu->arch.ia32_tsc_adjust_msr;
> +			tsc_state.flags |= KVM_TSC_STATE_TSC_ADJUST_VALID;
> +		}

This is mostly useful for userspace that doesn't disable the quirk, right?

> +		kvm_get_walltime(&wall_nsec, &host_tsc);
> +		diff = wall_nsec - tsc_state.nsec;
> +
> +		if (diff < 0 || tsc_state.nsec == 0)
> +			diff = 0;
> +

diff < 0 should be okay.  Also why the nsec==0 special case?  What about 
using a flag instead?

Paolo


  reply	other threads:[~2020-11-30 14:35 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-30 13:35 [PATCH 0/2] RFC: Precise TSC migration Maxim Levitsky
2020-11-30 13:35 ` [PATCH 1/2] KVM: x86: implement KVM_SET_TSC_PRECISE/KVM_GET_TSC_PRECISE Maxim Levitsky
2020-11-30 14:33   ` Paolo Bonzini [this message]
2020-11-30 15:58     ` Maxim Levitsky
2020-11-30 17:01       ` Paolo Bonzini
2020-12-01 19:43   ` Thomas Gleixner
2020-12-03 11:11     ` Maxim Levitsky
2020-11-30 13:35 ` [PATCH 2/2] KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS Maxim Levitsky
2020-11-30 13:54   ` Paolo Bonzini
2020-11-30 14:11     ` Maxim Levitsky
2020-11-30 14:15       ` Paolo Bonzini
2020-11-30 15:33         ` Maxim Levitsky
2020-11-30 13:38 ` [PATCH 0/2] RFC: Precise TSC migration (summary) Maxim Levitsky
2020-11-30 16:54 ` [PATCH 0/2] RFC: Precise TSC migration Andy Lutomirski
2020-11-30 16:59   ` Paolo Bonzini
2020-11-30 19:16 ` Marcelo Tosatti
2020-12-01 12:30   ` Maxim Levitsky
2020-12-01 19:48     ` Marcelo Tosatti
2020-12-03 11:39       ` Maxim Levitsky
2020-12-03 20:18         ` Marcelo Tosatti
2020-12-07 13:00           ` Maxim Levitsky
2020-12-01 13:48   ` Thomas Gleixner
2020-12-01 15:02     ` Marcelo Tosatti
2020-12-03 11:51       ` Maxim Levitsky
2020-12-01 14:01   ` Thomas Gleixner
2020-12-01 16:19     ` Andy Lutomirski
2020-12-03 11:57       ` Maxim Levitsky
2020-12-01 19:35 ` Thomas Gleixner
2020-12-03 11:41   ` Paolo Bonzini
2020-12-03 12:47   ` Maxim Levitsky

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