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

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Date:	Fri, 12 Oct 2012 09:52:17 +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 Thu, 2012-10-11 at 22:57 +0100, Mukesh Rathor wrote:
> PVH: make gdt_frames[]/gdt_ents into a union with {gdtaddr, gdtsz}, PVH
> only needs to send down gdtaddr and gdtsz. irq.c: PVH uses
> native_irq_ops. vcpu hotplug is currently not available for PVH.
> events.c: setup callback vector for PVH. Finally, PVH ring ops uses HVM
> paths for xenbus.
> 
> Signed-off-by: Mukesh R <mukesh.rathor@...cle.com>
> ---
>  arch/x86/include/asm/xen/interface.h |    8 +++++++-
>  arch/x86/xen/irq.c                   |    5 ++++-
>  arch/x86/xen/p2m.c                   |    2 +-
>  arch/x86/xen/smp.c                   |    4 ++--
>  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?)

Ian.

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