Re: [Qemu-devel] [PATCH v2 3/8] nvdimm acpi: introduce _FIT

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 12 Oct 2016 16:20:07 +0800
Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:

> On 10/11/2016 07:49 PM, Igor Mammedov wrote:
> > On Mon, 10 Oct 2016 21:09:30 +0800
> > Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:
> >  
> >> On 10/10/2016 08:51 PM, Igor Mammedov wrote:  
> >>> On Sat, 8 Oct 2016 15:17:14 +0800
> >>> Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:
> >>>  
> >>>> On 09/30/2016 09:14 PM, Igor Mammedov wrote:  
> >>>>> On Fri, 12 Aug 2016 14:54:05 +0800
> >>>>> Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:
> >>>>>  
> >>>>>> _FIT is required for hotplug support, guest will inquire the updated
> >>>>>> device info from it if a hotplug event is received
> >>>>>>
> >>>>>> As FIT buffer is not completely mapped into guest address space, so a
> >>>>>> new function, Read FIT whose function index is 0xFFFFFFFF, is reserved
> >>>>>> by QEMU to read the piece of FIT buffer. The buffer is concatenated
> >>>>>> before _FIT return  
> >>>>> Only issuer of UUID 2F10E7A4-9E91-11E4-89D3-123B93F75CBA can reserve
> >>>>> 0xFFFFFFFF for some purposes.
> >>>>> So spec should be amended first or custom generated UUID should be used.  
> >>>>
> >>>> Okay.
> >>>>
> >>>> I will change the changelog to reflect this fact and move the spec update
> >>>> to this patch.  
> >>> under spec, I've meant ACPI spec where this UUID is declared  
> >>
> >> Er. ACPI spec just said that "0xFFFF is reserved", not sure it will be used
> >> in the future.
> >>
> >> I'd prefer to custom-generated UUID, however, currently the UUID is checked
> >> in OSPM, i.e, QEMU is not able to distinguish other UUIDs,  
> > I'd go with custom-generated UUID
> >  
> >> so how about
> >> drop the UUID check in ACPI and pass the UUID info to QEMU?  
> > It's a bit late to do so as it would be qemu-guest ABI change and
> > one would need to maintain old and new protocol.
> >  
> 
> Okay.
> 
> How about extract 16 bits from 'handle' filed in NvdimmDsmIn buffer and use
> it to indicate different UUIDs, i,e:
> struct NvdimmDsmIn {
>      uint16_t handle;
>      uint16_t uuid_type;
>      uint32_t revision;
>      uint32_t function;
>      /* the remaining size in the page is used by arg3. */
>      union {
>          uint8_t arg3[4084];
>      };
> } QEMU_PACKED;
> typedef struct NvdimmDsmIn NvdimmDsmIn;
> 
> For this case, we set uuid_type = 1 to indicate the UUID is the one used
> for RFIT.
> 
> u16 for 'handle' is large enough as QEMU supports 255 memory devices.
I wouldn't do above as it needlessly complicates qemu<->OSPM
protocol.
Since handle is completely internal QEMU thing we can just reserve 0xFFFFFFFF value
in docs/specs/acpi_nvdimm.txt  for RFIT and keep UUID checks only on ASL side.

and on QEMU side add check to guaranty that auto generated handle for DIMMs
would never go into reserved range.