linux-kernel - Re: [PATCH v12 02/18] xen/pvh/x86: Define what an PVH guest is (v2).

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Message-ID: <52C549F1.8070005@citrix.com>
Date:	Thu, 2 Jan 2014 11:13:53 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	<boris.ostrovsky@...cle.com>, <stefano.stabellini@...citrix.com>,
	<mukesh.rathor@...cle.com>
Subject: Re: [PATCH v12 02/18] xen/pvh/x86: Define what an PVH guest is (v2).

On 01/01/14 04:35, Konrad Rzeszutek Wilk wrote:
> From: Mukesh Rathor <mukesh.rathor@...cle.com>
> 
> Which is a PV guest with auto page translation enabled
> and with vector callback. It is a cross between PVHVM and PV.
> 
> The Xen side defines PVH as (from docs/misc/pvh-readme.txt,
> with modifications):
> 
> "* the guest uses auto translate:
>  - p2m is managed by Xen
>  - pagetables are owned by the guest
>  - mmu_update hypercall not available
> * it uses event callback and not vlapic emulation,
> * IDT is native, so set_trap_table hcall is also N/A for a PVH guest.
> 
> For a full list of hcalls supported for PVH, see pvh_hypercall64_table
> in arch/x86/hvm/hvm.c in xen.  From the ABI prespective, it's mostly a
> PV guest with auto translate, although it does use hvm_op for setting
> callback vector."
> 
> We don't have yet a Kconfig entry setup as we do not
> have all the parts ready for it - so we piggyback
> on the PVHVM config option. This scaffolding will
> be removed later.
> 
> Note that on ARM the concept of PVH is non-existent. As Ian
> put it: "an ARM guest is neither PV nor HVM nor PVHVM.
> It's a bit like PVH but is different also (it's further towards
> the H end of the spectrum than even PVH).". As such these
> options (PVHVM, PVH) are never enabled nor seen on ARM
> compilations.
[...]
> --- a/include/xen/xen.h
> +++ b/include/xen/xen.h
> @@ -29,4 +29,20 @@ extern enum xen_domain_type xen_domain_type;
>  #define xen_initial_domain()	(0)
>  #endif	/* CONFIG_XEN_DOM0 */
>  
> +#ifdef CONFIG_XEN_PVHVM
> +/* Temporarily under XEN_PVHVM, but will be under CONFIG_XEN_PVH */

This is a bit confusing.  I think it would be better to add the
CONFIG_XEN_PVH option with this patch but make it default n and not
possible to enable.

David
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