linux-kernel - RE: [PATCH v5 1/3] x86/hyper-v: Suspend/resume the hypercall page for hibernation

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Message-ID: <PU1P153MB0169804D32B95E0A145CD0B9BF820@PU1P153MB0169.APCP153.PROD.OUTLOOK.COM>
Date:   Mon, 30 Sep 2019 18:49:33 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     vkuznets <vkuznets@...hat.com>
CC:     "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>, "bp@...en8.de" <bp@...en8.de>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: RE: [PATCH v5 1/3] x86/hyper-v: Suspend/resume the hypercall page for
 hibernation

> From: Vitaly Kuznetsov <vkuznets@...hat.com>
> Sent: Friday, September 27, 2019 2:05 AM
> To: Dexuan Cui <decui@...rosoft.com>
> 
> Dexuan Cui <decui@...rosoft.com> writes:
> ...
> > So, I'm pretty sure no IPI can happen between hv_suspend() and
> hv_resume().
> > self-IPI is not supposed to happen either, since interrupts are disabled.
> >
> > IMO TLB flush should not be an issue either, unless the kernel changes page
> > tables between hv_suspend() and hv_resume(), which is not the case as I
> > checked the related code, but it looks in theory that might happen, say, in
> > the future, so if you insist we should save the variable "hv_hypercall_pg"
> > to a temporary variable and set the "hv_hypercall_pg" to NULL before we
> > disable the hypercall page
> 
> Let's do it as a future proof so we can keep relying on !hv_hypercall_pg
> everywhere we need. No need to change this patch IMO, a follow-up would
> do.
> Vitaly

Now I think it would be better to do it in this patch. :-)
I'll post a v6 to follow your suggestion.

Thanks,
-- Dexuan