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

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Date:	Mon, 16 Nov 2015 13:04:28 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	Joao Martins <joao.m.martins@...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 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.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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