linux-kernel - Re: [Xen-devel] [PATCH v11 05/12] xen/pvh: Update E820 to work with PVH

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Date:	Wed, 18 Dec 2013 18:25:15 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	<boris.ostrovsky@...cle.com>, <david.vrabel@...rix.com>,
	<mukesh.rathor@...cle.com>, <jbeulich@...e.com>
Subject: Re: [Xen-devel] [PATCH v11 05/12] xen/pvh: Update E820 to work with
 PVH

On Tue, 17 Dec 2013, Konrad Rzeszutek Wilk wrote:
> From: Mukesh Rathor <mukesh.rathor@...cle.com>
> 
> In xen_add_extra_mem() we can skip updating P2M as it's managed
> by Xen. PVH maps the entire IO space, but only RAM pages need
> to be repopulated.
> 
> Signed-off-by: Mukesh Rathor <mukesh.rathor@...cle.com>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/xen/setup.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 2137c51..f93bca1 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -27,6 +27,7 @@
>  #include <xen/interface/memory.h>
>  #include <xen/interface/physdev.h>
>  #include <xen/features.h>
> +#include "mmu.h"
>  #include "xen-ops.h"
>  #include "vdso.h"
>  
> @@ -81,6 +82,9 @@ static void __init xen_add_extra_mem(u64 start, u64 size)
>  
>  	memblock_reserve(start, size);
>  
> +	if (xen_feature(XENFEAT_auto_translated_physmap))
> +		return;
> +
>  	xen_max_p2m_pfn = PFN_DOWN(start + size);
>  	for (pfn = PFN_DOWN(start); pfn < xen_max_p2m_pfn; pfn++) {
>  		unsigned long mfn = pfn_to_mfn(pfn);
> @@ -103,6 +107,7 @@ static unsigned long __init xen_do_chunk(unsigned long start,
>  		.domid        = DOMID_SELF
>  	};
>  	unsigned long len = 0;
> +	int xlated_phys = xen_feature(XENFEAT_auto_translated_physmap);
>  	unsigned long pfn;
>  	int ret;
>  
> @@ -116,7 +121,7 @@ static unsigned long __init xen_do_chunk(unsigned long start,
>  				continue;
>  			frame = mfn;
>  		} else {
> -			if (mfn != INVALID_P2M_ENTRY)
> +			if (!xlated_phys && mfn != INVALID_P2M_ENTRY)
>  				continue;
>  			frame = pfn;
>  		}
> @@ -154,6 +159,13 @@ static unsigned long __init xen_do_chunk(unsigned long start,
>  static unsigned long __init xen_release_chunk(unsigned long start,
>  					      unsigned long end)
>  {
> +	/*
> +	 * Xen already ballooned out the E820 non RAM regions for us
> +	 * and set them up properly in EPT.
> +	 */
> +	if (xen_feature(XENFEAT_auto_translated_physmap))
> +		return end - start;
> +
>  	return xen_do_chunk(start, end, true);
>  }
>  
> @@ -222,6 +234,9 @@ static void __init xen_set_identity_and_release_chunk(
>  	 * (except for the ISA region which must be 1:1 mapped) to
>  	 * release the refcounts (in Xen) on the original frames.
>  	 */
> +	if (xen_feature(XENFEAT_auto_translated_physmap))
> +		goto skip;
> +
>  	for (pfn = start_pfn; pfn <= max_pfn_mapped && pfn < end_pfn; pfn++) {
>  		pte_t pte = __pte_ma(0);
>  
> @@ -231,7 +246,7 @@ static void __init xen_set_identity_and_release_chunk(
>  		(void)HYPERVISOR_update_va_mapping(
>  			(unsigned long)__va(pfn << PAGE_SHIFT), pte, 0);
>  	}
> -
> +skip:
>  	if (start_pfn < nr_pages)
>  		*released += xen_release_chunk(
>  			start_pfn, min(end_pfn, nr_pages));

A goto? Really? What's wrong with an if?
Also considering that you are turning xen_release_chunk into a nop, the
only purpose of this function on PVH is to call set_phys_range_identity.
Can't we just do that?
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