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

[Maran Wilson <maran.wilson@oracle.com>]

On 3/13/2018 9:34 AM, Jan Beulich wrote:
>>>> On 13.03.18 at 17:20, <maran.wilson@oracle.com> 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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