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

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Message-ID: <56A8DFA4.5000801@oracle.com>
Date:	Wed, 27 Jan 2016 10:17:56 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"Luis R. Rodriguez" <mcgrof@...il.com>
Cc:	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 01/27/2016 10:09 AM, David Vrabel wrote:
> On 27/01/16 15:06, Boris Ostrovsky wrote:
>> On 01/27/2016 09:50 AM, David Vrabel wrote:
>>> 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.
>>
>> Why would we ever want to have a guest load microcode during boot? I can
>> see how a (privileged) guest may want to load microcode from a shell
>> (via microcode driver).
> I think you missed a word when you read my reply.

Yes, I missed it ;-)

Why not continue relying on paravirt_enabled()? We are going to keep 
this in some form for HVMlite.

-boris