On 23/06/15 13:39, Christoffer Dall wrote:
On Mon, Jun 22, 2015 at 09:44:48AM +0100, Peter Maydell wrote:
On 17 June 2015 at 10:00, Suzuki K. Poulose <suzuki.poulose@xxxxxxx> wrote:
From: "Suzuki K. Poulose" <suzuki.poulose@xxxxxxx>
This patch adds a generic ARM v8 KVM target cpu type for use
by the new CPUs which eventualy ends up using the common sys_reg
table. For backward compatibility the existing targets have been
preserved. Any new target CPU that can be covered by generic v8
sys_reg tables should make use of the new generic target.
How do you intend this to work for cross-host migration?
Is the idea that the kernel guarantees that "generic" looks
100% the same to the guest regardless of host hardware? I'm
not sure that can be made to work, given impdef differences
in ID register values, bp/wp registers, and so on.
Given that, it seems to me that we still need to provide
KVM_ARM_TARGET_$THISCPU defines so userspace can request
a specific guest CPU flavour; so what does this patch
provide that isn't already provided by just having userspace
query for the "preferred" CPU type as it does already?
I'm guessing the intention is to avoid having to add code in the kernel
to support KVM on a new CPU where nothing else needs to be done to
support KVM on that system.
Yes, thats the *only* motivation behind the patch and doesn't address
the migration issue. May be we can create a dummy set of values for
the ID registers, which doesn't provide any 'special functionality'
so that it is safe to be migrated across any host ?
Wrt. migration, I was also wondering about this. Would the differences
in the CPU architecture be detected when feeding back the invariant
sysregs from userspace on VM restore?
-Christoffer
Suzuki
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