Hi Oliver,
On 6/12/24 13:30, Oliver Upton wrote:
Hi Shaoqin,
On Tue, Jun 11, 2024 at 10:35:50PM -0400, Shaoqin Huang wrote:
Hi guys,
I'm trying to enable migration from MtCollins(Ampere Altra, ARMv8.2+) to
AmpereOne(AmpereOne, ARMv8.6+), the migration always fails when migration from
MtCollins to AmpereOne due to some register fields differing between the
two machines.
In this patch series, we try to make more register fields writable like
ID_AA64PFR1_EL1.BT. This is first step towards making the migration possible.
Some other hurdles need to be overcome. This is not sufficient to make the
migration successful from MtCollins to AmpereOne.
It isn't possible to transparently migrate between these systems. The
former has a cntfrq of 25MHz, and the latter has a cntfrq of 1GHz. There
isn't a mechanism for scaling the counter frequency, and I have zero
appetite for a paravirt interface.
Thanks for letting me know the cntfrq will block the migration between
the two machine. And we don't have the solution for it, which means it's
impossible to migrate between these systems which have different cntfrq.
On top of that, erratum AC03_CPU_38 seems to make a migration from
Neoverse-N1 to AmpereOne quite perilous, unless you hide FEAT_HAFDBS on
the source.
These issues are separate, though, from any possible changes to the
writability of ID_AA64PFR1_EL1, which still may be useful to userspace.
I think I can still making the ID_AA64PFR1_EL1 writable to enable
migration on some other machines.
Thanks,
Shaoqin
--
Shaoqin
