[PATCH] arm64/kvm: Add generic v8 KVM target

Hi Christoffer,

On 24/06/15 09:51, Christoffer Dall wrote:

On Wed, Jun 24, 2015 at 09:29:56AM +0100, Marc Zyngier wrote:

quoted

On 22/06/15 09:44, Peter Maydell wrote:

quoted

On 17 June 2015 at 10:00, Suzuki K. Poulose [off-list ref] wrote:

quoted

From: "Suzuki K. Poulose" <suzuki.poulose@arm.com>

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?

It is not meant to work for cross migration at all.

quoted

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?

The way I see this working is that a "generic" CPU cannot be migrated
(because we don't know anything about it). If it can be identified as a
known (non generic) implementation, then we can migrate it.

Concretely, how should this work?  Be enforced by userspace or should we
deny certain SET_ONE_REG operations from working on this target?

I can definitely see MIDR overriding failing on a generic CPU. Also, you
shouldn't be able to select a generic CPU if we know about the physical CPU.

Also, can we imagine any scenario where the generic CPU cannot me
modeled for a VM on a specific piece of hardware (current or future)?

What is the definition of a generic CPU here? In the above, generic
really means "Unknown", so I can't immediately see what it would mean to
model this.

	M.
-- 
Jazz is not dead. It just smells funny...