linux-kernel - Re: [PATCH] xen/x86: Adjust stack pointer in xen

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Date:	Tue, 17 Nov 2015 10:53:58 +0000
From:	Joao Martins <joao.m.martins@...cle.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	xen-devel <xen-devel@...ts.xen.org>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [PATCH] xen/x86: Adjust stack pointer in xen_sysexit



On 11/16/2015 09:04 PM, Andy Lutomirski wrote:
> On Mon, Nov 16, 2015 at 1:03 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@...cle.com> wrote:
>> On Mon, Nov 16, 2015 at 12:50:19PM -0800, Andy Lutomirski wrote:
>>> On Mon, Nov 16, 2015 at 12:48 PM, Boris Ostrovsky
>>> <boris.ostrovsky@...cle.com> wrote:
>>>> On 11/16/2015 03:22 PM, Borislav Petkov wrote:
>>>>>
>>>>> On Mon, Nov 16, 2015 at 12:11:11PM -0800, Andy Lutomirski wrote:
>>>>>
>>>>>> Are there really multiple feature bits for this stuff?  I'd like to
>>>>>> imagine that the entry code is all either Xen PV or native/PVH/PVHVM
>>>>>> -- i.e. I assumed that PVH works like native for all entries.
>>>>
>>>>
>>>>
>>>> Almost. For PVH we will have a small stub to set up bootparams and such but
>>>> then we jump to startup_{32|64} code.
>>>>
>>>>
>>>>> I just reacted to Boris' statement:
>>>>>
>>>>> "We don't currently have a Xen-specific CPU feature. We could, in
>>>>> principle, add it but we can't replace all of current paravirt patching
>>>>> with a single feature since PVH guests use a subset of existing pv ops
>>>>> (and in the future it may become even more fine-grained)."
>>>>
>>>>
>>>> Actually, nevermind this --- I was thinking about APIC ops and they are not
>>>> pv ops.
>>>>
>>>> Note though that there are other users of pv ops --- lguest and looks like
>>>> KVM (for one op) use them too.
>>>>
>>>
>>> Honestly, I think we should just delete lguest some time soon.  And
>>> KVM uses this stuff so lightly that we shouldn't need all of the pvop
>>> stuff.  (In fact, I'm slowly working on removing KVM_GUEST's
>>> dependency on PARAVIRT.)
>>
>> Even for the pvclock?
>>
>> (sorry for stealing this thread on this subject).
> 
> I don't think that pvclock uses any of the paravirt infrastructure.
> It's just another clock source AFAIK.
> 
Yeah, but pv_time_ops is still used on both Xen and KVM. Even though it looks
that on KVM some of it's used only when pvclock isn't marked as stable (i.e. no
PVCLOCK_TSC_STABLE_BIT).

Joao

> --Andy
> 
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