EFI image - SAL_DESC_PLATFORM_FEATURE bits

[Jes Sorensen <jes@sgi.com>]

Hi Tristan,

I have a problem with the EFI image under KVM (well it would be relevant
under Xen too).

Basically our system has the ITC_drift bit set in the
SAL_DESC_PLATFORM_FEATURE entry in the SAL table, due to the fact that
the ITC isn't synchronized throughout the system.

However looking at how Linux picks this up, I realize that this
information is propagated through the SAL sys_entry table rather than
through a SAL call, which would have been dead easy to emulate.

So my question is how your EFI image builds the sys_entry table? Is it
possible for KVM/Xen etc. to pass down information that the system clock
drifts or does it need to be hardcoded in the image? If the latter, do
you have any pointers to how one goes about rebuilding the image?

Right now I have a particularly bad setup where my test system has CPUs
of different clock speeds, plus the ITC isn't stable, so the time seen
by my guest kernels bounces left right and center depending on which
physical CPU it is running on at a given moment :-(

Linux is capable of handling drifting ITCs already, so I don't think it
would be a problem for us to hardcode this bit. No idea whether or not
Windows even looks at it?

Cheers,
Jes