Re: [Xen-devel] [PATCH v5 4/9] xen/x86: populate PVHv2 Dom0 physical memory map

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.01.17 at 20:48, <tim@xxxxxxx> wrote:
> At 09:40 -0700 on 27 Jan (1485510008), Jan Beulich wrote:
>> - vmx_set_segment_register() should initialize the TSS every
>>   time (including setting the I/O bitmap address to no lower
>>   than 32)
> 
> Probably to no lower than 136, to avoid having the bits of that field
> itself appearing in either the IO or interrupt bitmap.

Indeed.

>> - hvmloader's init_vm86_tss() will need to allocate 160 bytes
>>   rather than 128 (and we should expose this number, so that
>>   Roger can also use it)
>> 
>> Perhaps we should even introduce a hypercall for hvmloader
>> to query the needed value, rather than exposing a hardcoded
>> number?
> 
> I think Andrew's suggestion of just using a whole page is a good
> one.  The TSS is a 32-bit one, after all, and doesn't need to live in
> BIOS space.

Hmm, any size increase will need to come with further changes,
as it looks, including the use of a new HVM param: The VM86_TSS
param is being migrated, and hence for an incoming VM we need
to be able to tell whether the guest has set aside 128 bytes or a
full page. This of course implies that we need to keep Xen handle
the 128-byte case, too.

And if we somehow expect that a single page may not suffice in
the future, it may even be advisable to store an (address,size)
pair as param.

Jan


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