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From: Wei Liu <wei.liu@kernel.org>
To: Michael Kelley <mikelley@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>,
	Praveen Kumar <kumarpraveen@linux.microsoft.com>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Dexuan Cui <decui@microsoft.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"bp@alien8.de" <bp@alien8.de>, "x86@kernel.org" <x86@kernel.org>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"viremana@linux.microsoft.com" <viremana@linux.microsoft.com>,
	Sunil Muthuswamy <sunilmut@microsoft.com>,
	"nunodasneves@linux.microsoft.com"
	<nunodasneves@linux.microsoft.com>
Subject: Re: [PATCH] hyperv: root partition faults writing to VP ASSIST MSR PAGE
Date: Tue, 20 Jul 2021 16:29:23 +0000	[thread overview]
Message-ID: <20210720162923.rsbl24v5lujbiddj@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <MWHPR21MB15938E4E72E1A3EB3744AD53D7E29@MWHPR21MB1593.namprd21.prod.outlook.com>

On Tue, Jul 20, 2021 at 04:20:44PM +0000, Michael Kelley wrote:
> From: Wei Liu <wei.liu@kernel.org> Sent: Tuesday, July 20, 2021 6:35 AM
> > 
> > On Tue, Jul 20, 2021 at 06:55:56PM +0530, Praveen Kumar wrote:
> > [...]
> > > >
> > > >> +	if (hv_root_partition &&
> > > >> +	    ms_hyperv.features & HV_MSR_APIC_ACCESS_AVAILABLE) {
> > > >
> > > > Is HV_MSR_APIC_ACCESS_AVAILABLE a root only flag? Shouldn't non-root
> > > > kernel check this too?
> > >
> > > Yes, you are right. Will update this in v2. thanks.
> > 
> > Please split adding this check to its own patch.
> > 
> > Ideally one patch only does one thing.
> > 
> > Wei.
> > 
> 
> I was just looking around in the Hyper-V TLFS, and I didn't see
> anywhere that the ability to set up a VP Assist page is dependent
> on HV_MSR_APIC_ACCESS_AVAILABLE.  Or did I just miss it?

The feature bit Praveen used is wrong and should be fixed.

Per internal discussion this is gated by the AccessIntrCtrlRegs bit.

Wei.

> 
> Maybe the VP Assist page is not useful for the APIC EOI optimization
> Purposes if !HV_MSR_APIC_ACCESS_AVAILABLE, but the VP Assist
> page has other uses, such as for nested enlightenments.  So I
> wonder if the VP Assist page setup really should be gated on
> HV_MSR_APIC_ACCESS_AVAILABLE.
> 
> Michael

  reply	other threads:[~2021-07-20 16:31 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-19 18:51 Praveen Kumar
2021-07-20 11:20 ` Wei Liu
2021-07-20 13:25   ` Praveen Kumar
2021-07-20 13:35     ` Wei Liu
2021-07-20 16:20       ` Michael Kelley
2021-07-20 16:29         ` Wei Liu [this message]
2021-07-21  4:10           ` Michael Kelley
2021-07-21  7:12             ` Praveen Kumar
2021-07-21 10:10               ` Wei Liu
2021-07-21 11:32                 ` Praveen Kumar
2021-07-21 15:07                   ` Michael Kelley

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