Re: [Xen-devel] [PATCH v3 1/4] x86/PVHv2: Add memory map pointer to hvm_start_info struct

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

On Fri, Mar 16, 2018 at 05:29:27AM -0600, Jan Beulich wrote:
> >>> On 16.03.18 at 12:11, <roger.pau@xxxxxxxxxx> wrote:
> > On Thu, Mar 15, 2018 at 02:33:09PM -0700, Maran Wilson wrote:
> >> @@ -48,6 +49,15 @@
> >>   * 32 +----------------+
> >>   *    | rsdp_paddr     | Physical address of the RSDP ACPI data structure.
> >>   * 40 +----------------+
> >> + *    | memmap_paddr   | Physical address of the (optional) memory map. 
> >> Only
> >> + *    |                | present in version 1 and newer of the structure.
> >> + * 48 +----------------+
> >> + *    | memmap_entries | Number of entries in the memory map table. Zero
> >> + *    |                | if there is no memory map being provided. Only
> > 
> > Again (as I've mentioned in previous reviews) the way to signal a
> > non-present memory map is to set memmap_paddr to 0, not memmap_entries
> > to 0. This is already covered by the comment at the top of the header,
> > which states:
> > 
> > NOTE: nothing will be loaded at physical address 0, so a 0 value in any
> > of the address fields should be treated as not present.
> 
> I still think it is legitimate to direct consumers to look at the entry
> count here.

We have another similar field tuple already, modlist_paddr and
nr_modules and in that case (according to the current comments) the
proper way to check if there are modules is to check modlist_paddr !=
0 and then get the count from nr_modules.

Using this access strategy we avoid adding more comments about
checking nr_modules != 0 before trying to access modlist_paddr.

Roger.

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