Re: [Xen-devel] [v7][PATCH 07/16] hvmloader/e820: construct guest e820 table

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2015/7/14 17:32, Jan Beulich wrote:
> > > > On 14.07.15 at 07:22, <tiejun.chen@xxxxxxxxx> 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.
Before we probably relocate RAM,

low_mem_end = hvm_info->low_mem_pgend << PAGE_SHIFT

and the e820 entry specific to low memory,

[e820[X].addr, end]

Here, end = e820[X].addr + e820[X].size;

Now low_mem_end = end.

After that, low_mem_end < end. so if

(low_mem_end > e820[X].addr && low_mem_end < end) is true, this means 
that associated RAM entry is hitting, right? Then we need to revise this 
entry as [e820[X].addr, low_mem_end], and compensate [end - low_mem_end] 
to high memory. Anything I'm still wrong here?
Thanks
Tiejun

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