Re: [Qemu-devel] [PATCH v2 06/11] nvdimm acpi: initialize the resource used by NVDIMM ACPI

[Igor Mammedov]

On Mon, 15 Feb 2016 18:13:38 +0800
Xiao Guangrong <address@hidden> wrote:

> On 02/15/2016 05:18 PM, Michael S. Tsirkin wrote:
> > On Mon, Feb 15, 2016 at 10:11:05AM +0100, Igor Mammedov wrote:  
> >> On Sun, 14 Feb 2016 13:57:27 +0800
> >> Xiao Guangrong <address@hidden> wrote:
> >>  
> >>> On 02/08/2016 07:03 PM, Igor Mammedov wrote:  
> >>>> On Wed, 13 Jan 2016 02:50:05 +0800
> >>>> Xiao Guangrong <address@hidden> wrote:
> >>>>  
> >>>>> 32 bits IO port starting from 0x0a18 in guest is reserved for NVDIMM
> >>>>> ACPI emulation. The table, NVDIMM_DSM_MEM_FILE, will be patched into
> >>>>> NVDIMM ACPI binary code
> >>>>>
> >>>>> OSPM uses this port to tell QEMU the final address of the DSM memory
> >>>>> and notify QEMU to emulate the DSM method  
> >>>> Would you need to pass control to QEMU if each NVDIMM had its whole
> >>>> label area MemoryRegion mapped right after its storage MemoryRegion?
> >>>>  
> >>>
> >>> No, label data is not mapped into guest's address space and it only
> >>> can be accessed by DSM method indirectly.  
> >> Yep, per spec label data should be accessed via _DSM but question
> >> wasn't about it,  
> 
> Ah, sorry, i missed your question.
> 
> >> Why would one map only 4Kb window and serialize label data
> >> via it if it could be mapped as whole, that way _DMS method will be
> >> much less complicated and there won't be need to add/support a protocol
> >> for its serialization.
> >>  
> >
> > Is it ever accessed on data path? If not I prefer the current approach:  
> 
> The label data is only accessed via two DSM commands - Get Namespace Label
> Data and Set Namespace Label Data, no other place need to be emulated.
> 
> > limit the window used, the serialization protocol seems rather simple.
> >  
> 
> Yes.
> 
> Label data is at least 128k which is big enough for BIOS as it allocates
> memory at 0 ~ 4G which is tight region. It also needs guest OS to support
> lager max-xfer (the max size that can be transferred one time), the size
> in current Linux NVDIMM driver is 4k.
> 
> However, using lager DSM buffer can help us to simplify NVDIMM hotplug for
> the case that too many nvdimm devices present in the system and their FIT
> info can not be filled into one page. Each PMEM-only device needs 0xb8 bytes
> and we can append 256 memory devices at most, so 12 pages are needed to
> contain this info. The prototype we implemented is using ourself-defined
> protocol to read piece of _FIT and concatenate them before return to Guest,
> please refer to:
> https://github.com/xiaogr/qemu/commit/c46ce01c8433ac0870670304360b3c4aa414143a
> 
> As 12 pages are not small region for BIOS and the _FIT size may be extended 
> in the
> future development (eg, if PBLK is introduced) i am not sure if we need this. 
> Of
> course, another approach to simplify it is that we limit the number of NVDIMM
> device to make sure their _FIT < 4k.
My suggestion is not to have only one label area for every NVDIMM but
rather to map each label area right after each NVDIMM's data memory.
That way _DMS can be made non-serialized and guest could handle
label data in parallel.

As for a _FIT we can use the same approach as mem hotplug
(IO port window) or Michael's idea to add vendor specific
PCI_config region to a current PM device to avoid using
IO ports.


> 
> 
> 
> 
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