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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 18:01:16 +0100	[thread overview]
Message-ID: <005aaf41-9376-d535-211f-9ff08e53bcc4@redhat.com> (raw)
In-Reply-To: <ee06976738dff35e387077ba73e6ab375963abbf.camel@redhat.com>

On 30/11/20 16:58, Maxim Levitsky wrote:
>> This is mostly useful for userspace that doesn't disable the quirk, right?
> Isn't this the opposite? If I understand the original proposal correctly,
> the reason that we include the TSC_ADJUST in the new ioctl, is that
> we would like to disable the special kvm behavior (that is disable the quirk),
> which would mean that tsc will jump on regular host initiated TSC_ADJUST write.
> 
> To avoid this, userspace would set TSC_ADJUST through this new interface.

Yeah, that makes sense.  It removes the need to think "I have to set TSC 
adjust before TSC".

> Do you think that this is an issue? If so I can make the code work with
> signed numbers.

Not sure if it's an issue, but I prefer to make the API "less 
surprising" for userspace.  Who knows how it will be used.

> About nsec == 0, this is to allow to use this API for VM initialization.
> (That is to call KVM_SET_TSC_PRECISE prior to doing KVM_GET_TSC_PRECISE)

I prefer using flags for that purpose.

Paolo


  reply	other threads:[~2020-11-30 17:03 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
2020-11-30 15:58     ` Maxim Levitsky
2020-11-30 17:01       ` Paolo Bonzini [this message]
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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