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Re: [Xen-devel] [PATCH 1/3] SMBIOS table passthrough support

On Tue, 2012-02-21 at 13:42 +0000, Ross Philipson wrote:
> > -----Original Message-----
> > From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx]
> > Sent: Tuesday, February 21, 2012 3:47 AM
> > To: Ross Philipson
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] [PATCH 1/3] SMBIOS table passthrough support
> > 
> > On Tue, 2012-02-21 at 02:56 +0000, Ross Philipson wrote:
> > > Updates to the layout of the HVM parameter and information page
> > > defined in hvm_info_table.h. The SMBIOS pass-through tables are
> > > written to the bottom half of this page.
> > 
> > We would like to eventually get rid of the HVM info page and would
> > certainly like to avoid adding anything further there. Could this data
> > not be supplied via xenstore? Certainly they could and should be for the
> > ones controlled by the flags entry which you add.
> > 
> > Ian.
> > 
> Ah I did not realize that. The original incarnation of this code came
> from 2+ years ago. I have no objection to using xenstore but I did not
> think xenstore was suitable for passing arbitrary blocks of binary
> data (i.e. the raw SMBIOS firmware tables). Perhaps I am incorrect in
> this assumption.

I think in principal binary data is supported, but its use is
discouraged. docs/misc/xenstore.txt talks about it a bit.

For well defined entries it should be reasonable to have human readable
content in xenstore which simply enable/disables the table and perhaps
contains some configuration values as appropriate.

For adding arbitrary tables I'm less sure what the right answer is.
Common header elements in human readable form, payload as hex encoded
strings or something? Seems a bit icky though.

> I am not sure what other mechanisms could be employed. In other code I
> use in out hvmloader, I pass an ACPI SSDT to the hvmloader at runtime.
> I use a little DMAish interface I built into qemu to push the SSDT to
> hvmloader while it is building the ACPI tables. Something like this
> could be used but I don't really want to get qemu involved in this
> operation.

Yes, I think we should avoid that too.

> I guess a third option might be to have a facility to load extra
> modules/files into the new domain at start time and specify their
> gpa's in xenstore. They could then be discarded after the initial
> domain setup is complete.

That might work. What do others around here think?


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