linux-kernel - Re: [PATCH 1/2] Xen: Delay remapping memory of pv-domain

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Date:	Wed, 29 Oct 2014 06:30:18 +0100
From:	Juergen Gross <jgross@...e.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH 1/2] Xen: Delay remapping memory of pv-domain

On 10/28/2014 06:34 PM, David Vrabel wrote:
> Can these patches be split up?  They're hard to review as-is.  e.g., the
> changes to page allocation look they could be split out.
>
> On 27/10/14 14:52, Juergen Gross wrote:
>> Early in the boot process the memory layout of a pv-domain is changed
>> to match the E820 map (either the host one for Dom0 or the Xen one)
>> regarding placement of RAM and PCI holes. This requires removing memory
>> pages initially located at positions not suitable for RAM and adding
>> them later at higher addresses where no restrictions apply.
>
> How does this impact Matt Rushton's recent change to ensure the
> relocated frames are contiguous?

It is simplifying it. :-)

The relocated frames are in the same sequence as before, just at
another location. As the remapping is done later, I don't have to be
careful not to cross a p2m leaf page boundary (allocating a new leaf
page is no problem now).

>
> The change was "xen/setup: Remap Xen Identity Mapped RAM" (4fbb67e3c87).
>
>> +	/* Update kernel mapping */
>> +	if (HYPERVISOR_update_va_mapping((unsigned long)__va(pfn << PAGE_SHIFT),
>> +					 mfn_pte(mfn, PAGE_KERNEL), 0)) {
>> +		WARN(1, "Failed to update kernel mapping for mfn=%ld pfn=%ld\n",
>> +		      mfn, pfn);
>> +		return 0;
>
> I think you need to check if this is a PFN for a high page before
> updating the mapping.

Really? I'm not aware of having removed such a check. If it is really
necessary it must have been missing before...


Juergen
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