linux-kernel - Re: [PATCH 1/6] xen/pvh: Support ParaVirtualized Hardware extensions.

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Date:	Tue, 23 Oct 2012 10:07:53 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	mukesh.rathor@...cle.com, Ian.Campbell@...rix.com,
	stefano.stabellini@...citrix.com
Subject: Re: [PATCH 1/6] xen/pvh: Support ParaVirtualized Hardware extensions.

> +/*
> + * Unmaps the page appearing at a particular GPFN from the specified guest's
> + * pseudophysical address space.
> + * arg == addr of xen_remove_from_physmap_t.
> + */
> +#define XENMEM_remove_from_physmap      15
> +struct xen_remove_from_physmap {
> +    /* Which domain to change the mapping for. */
> +    domid_t domid;
> +
> +    /* GPFN of the current mapping of the page. */
> +    xen_pfn_t gpfn;
> +};

I just realized that this a bit of unfortunate. We end up
with on 64-bit with this layout:

{
  0->1 [domid]
  2->7 [nothing]
  8->16 [gpfn]

}

which if one were to do a 32-bit build you would get:
{
 0->1 [domid]
 2->3 [nothing]
 4->7 [gpfn]
}
which means another compat layer in Xen.

So I think it makes sense to modify this to be 32 and 64-bit
clean, something like this:

{
	domid_t	domid;
	u8	pad[6];
	xen_pfn_t gpfn;
	/* xen_pfn_t under 32-bit x86 is 4 bytes, so extend it */
#ifdef CONFIG_X86_32
	__u8	pad1[4];
#endif
}

that way the structure is exactly the same size and the offsets
align.

Mukesh, you OK with that?
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