netdev - RE: [Patch v4 05/13] init: Call mem_encrypt_init() after Hyper-V hypercall init is done

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Date:   Tue, 6 Dec 2022 20:13:08 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
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Subject: RE: [Patch v4 05/13] init: Call mem_encrypt_init() after Hyper-V
 hypercall init is done

From: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> 
> 
> On 12/1/22 7:30 PM, Michael Kelley wrote:
> > Full Hyper-V initialization, including support for hypercalls, is done
> > as an apic_post_init callback via late_time_init().  mem_encrypt_init()
> > needs to make hypercalls when it marks swiotlb memory as decrypted.
> > But mem_encrypt_init() is currently called a few lines before
> > late_time_init(), so the hypercalls don't work.
> 
> Did you consider moving hyper-v hypercall initialization before
>  mem_encrypt_init(). Is there any dependency issue?

Hyper-V initialization has historically been done using the callbacks
that exist in the x86 initialization paths, rather than adding explicit
Hyper-V init calls.  As noted above, the full Hyper-V init is done on
the apic_post_init callback via late_time_init().  Conceivably we could
add an explicit call to do the Hyper-V init, but I think there's still a
problem in putting that Hyper-V init prior to the current location of
mem_encrypt_init().  I'd have to go check the history, but I think the
Hyper-V init needs to happen after the APIC is initialized.

It seems like moving mem_encrypt_init() slightly later is the cleaner
long-term solution.  Are you aware of a likely problem arising in the
future with moving mem_encrypt_init()?

Michael

> 
> >
> > Fix this by moving mem_encrypt_init() after late_time_init() and
> > related clock initializations. The intervening initializations don't
> > do any I/O that requires the swiotlb, so moving mem_encrypt_init()
> > slightly later has no impact.
> >