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From: Wei Liu <wei.liu@kernel.org>
To: Praveen Kumar <kumarpraveen@linux.microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>,
	linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
	kys@microsoft.com, haiyangz@microsoft.com,
	sthemmin@microsoft.com, decui@microsoft.com, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	viremana@linux.microsoft.com, sunilmut@microsoft.com,
	nunodasneves@linux.microsoft.com
Subject: Re: [PATCH v2] hyperv: root partition faults writing to VP ASSIST MSR PAGE
Date: Sat, 24 Jul 2021 15:43:20 +0000	[thread overview]
Message-ID: <20210724154320.apc7lm2pclfzig7n@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <bd019dc6-75e9-ac89-18fa-c09561000188@linux.microsoft.com>

On Thu, Jul 22, 2021 at 09:45:36PM +0530, Praveen Kumar wrote:
> > 
> > I think about this a bit more, the NULL check for *hvp in hv_cpu_init in
> > the original code is perhaps due to the code has opted to not free the
> > page when disabling the VP assist page. When the CPU is brought back
> > online, it does not want to allocate another page, but to use the one
> > that's already allocated.
> > 
> > So, since you listened to my suggestion to add a similar check, you need
> > to reset hv_vp_assist_page to NULL here. Alternatively the check for
> > *hvp can be dropped for the root path. Either way, the difference
> > between root and non-root should be documented.
> > 
> 
> I would make it as NULL post memunmap as you suggested, so that we
> don't end up reusing the old/cached value. Before doing that, is there
> any use-case where hypervisor can allocate or change the VP assist
> page that can impact root kernel execution ?

I don't think a sane hypervisor will change the page in such a way.

Wei.

      reply	other threads:[~2021-07-24 15:43 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-21 18:03 Praveen Kumar
2021-07-22  5:53 ` Michael Kelley
2021-07-22 10:27 ` Wei Liu
2021-07-22 16:15   ` Praveen Kumar
2021-07-24 15:43     ` Wei Liu [this message]

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