linux-kernel - Re: [PATCH v2 08/17] x86/hyperv: handling hypercall page setup for root

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Date:   Fri, 13 Nov 2020 16:09:07 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        Lillian Grassin-Drake <ligrassi@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 08/17] x86/hyperv: handling hypercall page setup for
 root

On Fri, Nov 13, 2020 at 03:33:33PM +0000, Wei Liu wrote:
> On Thu, Nov 12, 2020 at 04:51:09PM +0100, Vitaly Kuznetsov wrote:
> > Wei Liu <wei.liu@...nel.org> writes:
> > 
> > > When Linux is running as the root partition, the hypercall page will
> > > have already been setup by Hyper-V. Copy the content over to the
> > > allocated page.
> > >
> > > The suspend, resume and cleanup paths remain untouched because they are
> > > not supported in this setup yet.
> > 
> > What about adding BUG_ONs there then?
> 
> I generally avoid cluttering code if I'm sure it definitely does not
> work.
> 
> In any case, adding BUG_ONs is not the right answer. Both hv_suspend and
> hv_resume can return an error code. I would rather just do
> 
>    if (hv_root_partition)
>        return -EPERM;
> 
> in both places.

Correction: hv_resume is void, so I won't add that code snippet. But we
should still be fine because hv_suspend will have already failed in the
first place.

Wei.