Re: [Xen-devel] [RFC Design Doc] Add vNVDIMM support for Xen

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

On 02/29/16 05:04, Jan Beulich wrote:
> >>> On 29.02.16 at 12:52, <haozhong.zhang@xxxxxxxxx> wrote:
> > On 02/29/16 03:12, Jan Beulich wrote:
> >> >>> On 29.02.16 at 10:45, <haozhong.zhang@xxxxxxxxx> wrote:
> >> > On 02/29/16 02:01, Jan Beulich wrote:
> >> >> >>> On 28.02.16 at 15:48, <haozhong.zhang@xxxxxxxxx> wrote:
> >> >> > Anyway, we may avoid some conflicts between ACPI tables/objects by
> >> >> > restricting which tables and objects can be passed from QEMU to Xen:
> >> >> > (1) For ACPI tables, xen does not accept those built by itself,
> >> >> >     e.g. DSDT and SSDT.
> >> >> > (2) xen does not accept ACPI tables for devices that are not attached 
> >> >> > to
> >> >> >     a domain, e.g. if NFIT cannot be passed if a domain does not have
> >> >> >     vNVDIMM.
> >> >> > (3) For ACPI objects, xen only accepts namespace devices and requires
> >> >> >     their names does not conflict with existing ones provided by Xen.
> >> >> 
> >> >> And how do you imagine to enforce this without parsing the
> >> >> handed AML? (Remember there's no AML parser in hvmloader.)
> >> > 
> >> > As I proposed in last reply, instead of passing an entire ACPI object,
> >> > QEMU passes the device name and the AML code under the AML device entry
> >> > separately. Because the name is explicitly given, no AML parser is
> >> > needed in hvmloader.
> >> 
> >> I must not only have missed that proposal, but I also don't see
> >> how you mean this to work: Are you suggesting for hvmloader to
> >> construct valid AML from the passed in blob? Or are you instead
> >> considering to pass redundant information (name once given
> >> explicitly and once embedded in the AML blob), allowing the two
> >> to be out of sync?
> > 
> > I mean the former one.
> 
> Which will involve adding how much new code to it?
>

Because hvmloader only accepts AML device rather than arbitrary objects,
only code that builds the outmost part of AML device is needed. In ACPI
spec, an AML device is defined as
    DefDevice := DeviceOp PkgLength NameString ObjectList
hvmloader only needs to build the first 3 terms, while the last one is
passed from qemu.

Haozhong

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