Re: [PATCH 1/6] docs: update docs for the ~/platform/generation-id key

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 28/05/14 15:44, Ian Campbell wrote:
> On Tue, 2014-05-27 at 18:31 +0100, David Vrabel wrote:
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
>> ---
>>  docs/misc/xenstore-paths.markdown |   24 ++++++++++++++++--------
>>  1 file changed, 16 insertions(+), 8 deletions(-)
>>
>> diff --git a/docs/misc/xenstore-paths.markdown b/docs/misc/xenstore-paths.markdown
>> index 70ab7f4..41d7d6d 100644
>> --- a/docs/misc/xenstore-paths.markdown
>> +++ b/docs/misc/xenstore-paths.markdown
>> @@ -166,11 +166,6 @@ use the xenstore-based protocol instead (see ~/control/shutdown,
>>  below) even if the guest has advertised support for the event channel
>>  protocol.
>>  
>> -#### ~/hvmloader/generation-id-address = ADDRESS [r,HVM,INTERNAL]
>> -
>> -The hexadecimal representation of the address of the domain's
>> -"generation id".
>> -
>>  #### ~/hvmloader/allow-memory-relocate = ("1"|"0") [HVM,INTERNAL]
>>  
>>  If the default low MMIO hole (below 4GiB) is not big enough for all
>> @@ -193,9 +188,22 @@ Various platform properties.
>>  
>>  #### ~/platform/generation-id = INTEGER ":" INTEGER [HVM,INTERNAL]
>>  
>> -Two 64 bit values that represent the Windows Generation ID.
>> -Is used by the BIOS initializer to get this value.
>> -If not present or "0:0" (all zeroes) device will not be present to the machine.
>> +The upper and lower 64-bit words of the 128-bit VM Generation ID.
>> +
>> +This key is used by hvmloader to create the ACPI VM Generation ID
>> +device.  It initialises a 16 octet region of guest memory with this
>> +value.  The guest physical address of this region is saved in the
>> +HVM_PARAM_VM_GENERATION_ID_ADDR HVM parameter.
>> +
>> +If this key is not present, is empty, or is all-zeros ("0:0") then the
>> +ACPI device is not created.
>> +
>> +The toolstack should, before unpausing a created or restored HVM
>> +domain, set this key and write the same ID to the guest memory
>> +location in HVM_PARAM_VM_GENERATION_ID_ADDR (if this address is
>> +non-zero).
> Is the toolstack or hvmloader now responsible for writing this value to
> guest memory? It seems like it might be a shared responsibility via some
> mode of cooperation that I'm not following?
>
> Ian.

HVMLoader is responsible for allocating the space inside the guest to
start with, and for populating it with the initial value.

However, HVMLoader is *not* rerun on suspend/resume, so something
external in the toolstack needs to be able to update the value when needed.

~Andrew