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Re: [Xen-devel] [PATCH 1/1] x86/PVHv2: Add memory map pointer to hvm_start_info struct
On 3/13/2018 10:16 AM, Roger Pau Monné wrote:
On Tue, Mar 13, 2018 at 09:55:20AM -0700, Maran Wilson wrote:
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" ?
No, it needs to be in a public header, e820.h is private to Xen.
I would recommend that you list the types in this header, specifying
that the 'type' values are arch-specific, and that this is the x86
specific interface.
Can I provide that list in a comment block? Or are you saying you want
me to create new #define values in this header file to enumerate the
possible range of "type" values for x86 guests?
I'd prefer to avoid the latter since I would be redefining values that
most certainly are already defined in every source tree where this
header file is likely to show up. But if folks feel it is necessary,
I'll add the symbols here.
You likely also want to reference the section of
the ACPI spec where those types are defined, so that the reader can
figure out it's exact meaning.
Sure, I can add that. I'm thinking something like:
For x86 guests, please see "Address Range Types" as defined in
section 15 (System Address Map Interfaces) of the ACPI Specification
(http://uefi.org/specifications)
Thanks,
-Maran
Thanks, Roger.
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