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

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Message-ID: <CALCETrWhCxYaZmo0p8xfs0d482+SkY36-ZExbkN6W43Ui8tNZg@mail.gmail.com>
Date:	Mon, 16 Nov 2015 12:50:19 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	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>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH] xen/x86: Adjust stack pointer in xen_sysexit

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.)

--Andy


-- 
Andy Lutomirski
AMA Capital Management, LLC
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