From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@suse.com>
Subject: Re: [v7][PATCH 07/16] hvmloader/e820: construct guest
 e820 table
Date: Tue, 14 Jul 2015 10:32:00 +0100
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To: Tiejun Chen <tiejun.chen@intel.com>
Cc: Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, xen-devel@lists.xen.org, Keir Fraser <keir@xen.org>
List-Id: xen-devel@lists.xenproject.org

>>> On 14.07.15 at 07:22, <tiejun.chen@intel.com> wrote:
>>> +    for ( i = 0; i < memory_map.nr_map; i++ )
>>> +    {
>>> +        uint64_t end = e820[i].addr + e820[i].size;
>>
>> Either loop index/boundary or used array are wrong here: In the
>> earlier loop you copied memory_map[0...nr_map-1] to
>> e820[n...n+nr_map-1], but here you're looping looking at
>> e820[0...nr_map-1]
> 
> You're right. I should lookup all e820[] like this,
> 
> for ( i = 0; i < nr; i++ )

Hmm, I would have thought you only care about either part of
the just glued together map.

>>> +        if ( e820[i].type == E820_RAM &&
>>> +             low_mem_end > e820[i].addr && low_mem_end < end )
>>
>> Assuming you mean to look at the RDM e820[] entries here, this
>> is not a correct check: You don't care about partly or fully
>> contained, all you care about is whether low_mem_end extends
>> beyond the start of the region.
> 
> Here I'm looking at the e820 entry indicating low memory. Because
> 
> low_mem_end = hvm_info->low_mem_pgend << PAGE_SHIFT;
> 
> and when we allocate MMIO in pci.c, its possible to populate RAM so 
> hvm_info->low_mem_pgend would be changed over there. So we need to 
> compensate this loss with high memory. Here memory_map[] also records 
> the original low/high memory, so if low_mem_end is less-than the 
> original we need this compensation.

And I'm not disputing your intentions - I'm merely pointing out that
afaics the code above doesn't match these intentions. In particular
(as said) I don't see why you need to check low_mem_end < end.

Jan