Hi Christoffer, On 24/06/15 09:51, Christoffer Dall wrote: > On Wed, Jun 24, 2015 at 09:29:56AM +0100, Marc Zyngier wrote: >> On 22/06/15 09:44, 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? >> >> It is not meant to work for cross migration at all. >> >>> 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... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
