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

[Maran Wilson <maran.wilson@xxxxxxxxxx>]

On 3/13/2018 9:34 AM, Jan Beulich wrote:
> > > > On 13.03.18 at 17:20, <maran.wilson@xxxxxxxxxx> wrote:
> > On 3/13/2018 3:50 AM, Roger Pau Monné wrote:
> > > On Fri, Mar 02, 2018 at 12:54:29PM -0800, Maran Wilson wrote:
> > > > @@ -62,10 +72,34 @@
> > > >     *    | reserved       |
> > > >     * 32 +----------------+
> > > >     *
> > > > + * The layout of each entry in the memory map table is as follows:
> > > > + *
> > > > + *  0 +----------------+
> > > > + *    | addr           | Base address
> > > > + *  8 +----------------+
> > > > + *    | size           | Size of mapping in bytes
> > > > + * 16 +----------------+
> > > > + *    | type           | Type of mapping as defined between the hypervisor
> > > > + *    |                | and guest it's starting. E820_TYPE_xxx, for example.
> > > This needs a link to the expected type values (or a reference). Or you
> > > need to spell out the relation between the values and the memory types.
> > This field was discussed a good deal in v2 of the linux patches. I had
> > originally defined this to be a specific type field, matching the
> > x86/Linux definition for e820 memory mapping types. But Jan Beulich
> > successfully argued that we should keep the definition of this
> > particular interface agnostic to architecture and OS and not limit the
> > field to specific values. I believe the central idea behind Jan's
> > argument was to keep the interface x86-agnostic as well as preserving
> > the option to add additional memory mapping types in the future without
> > them being sanctioned by whoever maintains E820 type assignments.
> >
> > That's why I changed the comment wording to what it is now. Basically
> > spelling out the fact that this field simply needs to be agreed upon
> > between the producer and the consumer since a hypervisor should
> > generally know what type of guest it is starting. And I mentioned
> > e820_type_xxx as the *example* of one such implementation, since that is
> > the most obvious use case and the e820 types are part of the ACPI
> > standard (and thus easy to find/reference).
> But Roger makes a valid remark here. Statements like
> "E820_TYPE_xxx, for example" are simply to vague for a stable public
> interface.
How about "For example, E820 types like E820_RAM, E820_ACPI, etc as 
defined in xen/include/asm-x86/e820.h of the Xen tree" ?
Thanks,
-Maran

> Jan

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