linux-kernel - Re: [PATCH] x86/hyperv: Suspend/resume the VP assist page for hibernation

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Message-ID: <87blnqv389.fsf@vitty.brq.redhat.com>
Date:   Fri, 17 Apr 2020 12:03:18 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     bp@...en8.de, haiyangz@...rosoft.com, hpa@...or.com,
        kys@...rosoft.com, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        sthemmin@...rosoft.com, tglx@...utronix.de, x86@...nel.org,
        mikelley@...rosoft.com, wei.liu@...nel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] x86/hyperv: Suspend/resume the VP assist page for hibernation

Dexuan Cui <decui@...rosoft.com> writes:

> Unlike the other CPUs, CPU0 is never offlined during hibernation. So in the
> resume path, the "new" kernel's VP assist page is not suspended (i.e.
> disabled), and later when we jump to the "old" kernel, the page is not
> properly re-enabled for CPU0 with the allocated page from the old kernel.
>
> So far, the VP assist page is only used by hv_apic_eoi_write().

No, not only for that ('git grep hv_get_vp_assist_page')

KVM on Hyper-V also needs VP assist page to use Enlightened VMCS. In
particular, Enlightened VMPTR is written there.

This makes me wonder: how does hibernation work with KVM in case we use
Enlightened VMCS and we have VMs running? We need to make sure VP Assist
page content is preserved.

-- 
Vitaly