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From: Michael Kelley <mikelley@microsoft.com>
To: Wei Liu <wei.liu@kernel.org>,
	Praveen Kumar <kumarpraveen@linux.microsoft.com>
Cc: "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 16:20:44 +0000	[thread overview]
Message-ID: <MWHPR21MB15938E4E72E1A3EB3744AD53D7E29@MWHPR21MB1593.namprd21.prod.outlook.com> (raw)
In-Reply-To: <20210720133514.lurmus2lgffcldnq@liuwe-devbox-debian-v2>

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?

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 16:26 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 [this message]
2021-07-20 16:29         ` Wei Liu
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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