Re: [Xen-devel] [PATCH v2 15/30] xen/x86: populate PVHv2 Dom0 physical memory map

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

It seems like I've forgotten to answer one of your comments in a previous 
email, sorry.

On Fri, Sep 30, 2016 at 09:52:56AM -0600, Jan Beulich wrote:
> >>> On 27.09.16 at 17:57, <roger.pau@xxxxxxxxxx> wrote:
> > +     * VM86 TSS. Note that after this not all e820 regions will be aligned
> > +     * to PAGE_SIZE.
> > +     */
> > +    for ( i = 1; i <= d->arch.nr_e820; i++ )
> > +    {
> > +        entry = &d->arch.e820[d->arch.nr_e820 - i];
> > +        if ( entry->type != E820_RAM ||
> > +             entry->size < PAGE_SIZE + HVM_VM86_TSS_SIZE )
> > +            continue;
> > +
> > +        entry->size -= PAGE_SIZE + HVM_VM86_TSS_SIZE;
> > +        gaddr = entry->addr + entry->size;
> > +        break;
> > +    }
> > +
> > +    if ( gaddr == 0 || gaddr < MB(1) )
> > +    {
> > +        printk("Unable to find memory to stash the identity map and 
> > TSS\n");
> > +        return -ENOMEM;
> 
> One function up you panic() on error - please be consistent. Also for
> one of the other patches I think we figured that the TSS isn't really
> required, so please only warn in that case.

The allocation is done together for the ident PT and the TSS, and while 
the TSS is not mandatory the identity page-table is (or else Dom0 kernel 
won't boot at all on this kind of systems). In any case, it's almost 
impossible for this allocation to fail (because Xen is not actually 
allocating memory, just stealing a part of a RAM region that has already 
been populated).

Roger.

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