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Date: Wed, 13 Apr 2016 12:03:12 +0200
From: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>
To: Matt Fleming <matt@codeblueprint.co.uk>
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Subject: Re: [Xen-devel] HVMLite / PVHv2 - using x86 EFI boot entry
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On Wed, Apr 06, 2016 at 04:02:40PM +0100, Matt Fleming wrote:
[...]
> One place that struck me as suitable for this "hypercall in an EFI
> service stub" approach is the trouble with doing ACPI reboot as
> documented here,
> 
>   http://lists.xen.org/archives/html/xen-devel/2016-02/msg01609.html
> 
> Performing the reset hypercall from within HVMlite's custom EfiReset()
> service would avoid having to touch ACPICA at all, and would be
> indistinguishable from bare metal.

I don't get this, the "reset/shutdown" hypercall requires the following 
steps from Dom0 (it's not as simple as calling a hypercall):

The way to perform a full system power off from Dom0 is different than 
what's done in a DomU guest. In order to perform a power off from Dom0 the 
native ACPI path should be followed, but the guest should not write the 
`SLP_EN` bit to the Pm1Control register. Instead the 
`XENPF_enter_acpi_sleep` hypercall should be used, filling the following 
data in the `xen_platform_op` struct:

    cmd = XENPF_enter_acpi_sleep
    interface_version = XENPF_INTERFACE_VERSION
    u.enter_acpi_sleep.pm1a_cnt_val = Pm1aControlValue
    u.enter_acpi_sleep.pm1b_cnt_val = Pm1bControlValue

At which point it means that we are either going to duplicate ACPICA code 
into the HVMlite's custom EfiReset() service, or we are going to call into 
ACPICA, which is what we already do now.

Roger.