linux-kernel - Re: [PATCH 05/10] xen/pvh: Extend vcpu_guest

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Date:	Wed, 24 Oct 2012 10:49:00 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"mukesh.rathor@...cle.com" <mukesh.rathor@...cle.com>
Subject: Re: [PATCH 05/10] xen/pvh: Extend vcpu_guest_context, p2m, event,
 and XenBus.

On Tue, 2012-10-23 at 19:12 +0100, Konrad Rzeszutek Wilk wrote:
[...]
> +		/* GUEST_GDTR_BASE and */
> +		ctxt->u.pvh.gdtaddr = (unsigned long)gdt;
> +		/* GUEST_GDTR_LIMIT in the VMCS. */
> +		ctxt->u.pvh.gdtsz = (unsigned long)(GDT_SIZE - 1);
> +
> [...]
> -		ctxt->gdt_frames[0] = gdt_mfn;
> -		ctxt->gdt_ents      = GDT_ENTRIES;
> +		ctxt->u.pv.gdt_frames[0] = gdt_mfn;
> +		ctxt->u.pv.gdt_ents      = GDT_ENTRIES;

I guess I've been told and forgotten but why does this need to differ
between PV and PVH? Can the hypervisor not take the gfn in gdt_frames[0]
= gdt_mfn and figure out the gdtaddr from it? Is this because n the PV
case the H/V loads the GDT with the address of its own mapping of the
gdt_frames but in the PVH case we have no such mapping because the
pagetables don't have a Xen region in them?

It's worthy of a comment in any case.

[...]
> +	/* PVH TBD/FIXME: future work */
[...]
> +		/* PVH: TBD/FIXME: debug and fix eio map to work with pvh */

Do we really need these TODOs inline in the code? Especially in generic
code.

Ian.

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