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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan

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