linux-kernel - Re: [Xen-devel] [PATCH v1 04/12] xen/hvmlite: Bootstrap HVMlite guest

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Message-ID: <56A8D93C.6040304@citrix.com>
Date:	Wed, 27 Jan 2016 14:50:36 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"Luis R. Rodriguez" <mcgrof@...il.com>
CC:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Juergen Gross <jgross@...e.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>, <xen-devel@...ts.xenproject.org>,
	"Borislav Petkov" <bp@...e.de>,
	Roger Pau Monné <roger.pau@...rix.com>
Subject: Re: [Xen-devel] [PATCH v1 04/12] xen/hvmlite: Bootstrap HVMlite guest

On 27/01/16 14:42, Konrad Rzeszutek Wilk wrote:
> On Tue, Jan 26, 2016 at 08:54:56PM -0800, Luis R. Rodriguez wrote:
>> On Jan 26, 2016 6:16 PM, "Luis R. Rodriguez" <mcgrof@...e.com> wrote:
>>>
>>> On Tue, Jan 26, 2016 at 4:04 PM, Luis R. Rodriguez <mcgrof@...e.com>
>> wrote:
>>>> You go:
>>>>
>>>> hvmlite_start_xen() -->
>>>>         HVM stub
>>>>         startup_64() | (startup_32()
>>>
>>> Hrm, does HVMlite work well with load_ucode_bsp(), note the patches to
>>> rebrand pv_enabled() to pv_legacy() or whatever, this PV type will not
>>> be legacy or crap / old, so we'd need a way to catch it if we should
>>> not use that code for this PV type. This begs the question, are you
>>> also sure other callers in startup_32() or startup_64() might be OK as
>>> well where previously guarded with pv_enabled() ?
>>
>> Actually this call can't be used, and if early code used it prior to
>> setup_arch() it'd be a bug as its only properly set until later. Vetting
>> for correctness of all code call is still required though and perhaps we do
>> need something to catch now this PV type on early code such as this one if
>> we don't want it. From what I've gathered before on other bsp ucode we
>> don't want ucode loaded for PV guest types through these mechanisms.
> 
> It may help to not think of PVH/hvmlite as PV. It really is HVM with a lot
> of emulated devices removed.
> 
> How does early microcode work on EFI? Does the EFI stub code have an early
> microcode loading code ?

Surely the interesting comparison here is how is (early) microcode
loading disabled in KVM guests?  We should use the same mechanism for
HVMlite guests.

David