linux-kernel - Re: [Xen-devel] [PATCH V2 2/7]: PVH: use native irq, enable callback, use HVM ring ops, ...

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Message-ID: <1350291497.18058.5.camel@zakaz.uk.xensource.com>
Date:	Mon, 15 Oct 2012 09:58:17 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Mukesh Rathor <mukesh.rathor@...cle.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH V2 2/7]: PVH: use native irq, enable
 callback, use HVM ring ops, ...

On Fri, 2012-10-12 at 20:06 +0100, Mukesh Rathor wrote:
> On Fri, 12 Oct 2012 09:52:17 +0100
> Ian Campbell <Ian.Campbell@...rix.com> wrote:
> 
> > >  drivers/xen/cpu_hotplug.c            |    4 +++-
> > >  drivers/xen/events.c                 |    9 ++++++++-
> > >  drivers/xen/xenbus/xenbus_client.c   |    3 ++-
> > >  7 files changed, 27 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/arch/x86/include/asm/xen/interface.h
> > > b/arch/x86/include/asm/xen/interface.h index 555f94d..f11edb0 100644
> > > --- a/arch/x86/include/asm/xen/interface.h
> > > +++ b/arch/x86/include/asm/xen/interface.h
> > > @@ -143,7 +143,13 @@ struct vcpu_guest_context {
> > >      struct cpu_user_regs user_regs;         /* User-level CPU
> > > registers     */ struct trap_info trap_ctxt[256];        /* Virtual
> > > IDT                  */ unsigned long ldt_base, ldt_ents;       /*
> > > LDT (linear address, # ents) */
> > > -    unsigned long gdt_frames[16], gdt_ents; /* GDT (machine
> > > frames, # ents) */
> > > +    union {
> > > +	struct {
> > > +		/* PV: GDT (machine frames, # ents).*/
> > > +		unsigned long gdt_frames[16], gdt_ents;
> > > +	} s;
> > > +	unsigned long gdtaddr, gdtsz;	    /* PVH: GDTR addr
> > > and size */
> > 
> > I've pointed out a few times that I think this is wrong -- gdtaddr and
> > gdtsz will overlap each other in the union. I'm not sure how it even
> > works, unless the hypervisor is ignoring one or the other. You need:
> > 
> > union {
> > 	struct {
> > 		unsigned long gdt_frames[16], gdt_ents;
> > 	} pv;
> > 	struct {
> > 		unsigned long gdtaddr, gdtsz;
> > 	} pvh;
> > } gdt;
> > 
> > (I've gone with naming the union gdt instead of u. You might want
> > therefore to also drop the gdt prefix from the members?)
> 
> Is it worth it, I mean, making it a union. Would you be OK if I just
> used gdt_frames[0] and gdt_ends for gdtaddr and size?

What's the problem with making it a union? Seems like you are 80% of the
way there.

Why is this different between PV and PVH in the first place (at the API
level I mean, obviously the handling in the h/v will differ)?

At the very least gdtsz and gdt_ents are the same thing with different
units AFAICT and so can be combined.

How come you don't need the same stuff for ldt*?

Ian.


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