Re: [RFC PATCH v2 3/5] target/arm/kvm: Implement virtual time adjustment

[Peter Maydell <peter.maydell@linaro.org>]

On Mon, 16 Dec 2019 at 15:14, Peter Maydell <peter.maydell@linaro.org> wrote:
> How does this interact with the usual register sync to/from
> KVM (ie kvm_arch_get_registers(), which I think will do a
> GET_ONE_REG read of the TIMER_CNT register the way it does
> any other sysreg, inside write_kvmstate_to_list(), plus
> kvm_arch_set_registers() which does the write back to the
> kernel in write_list_to_kvmstate()) ? Presumably we want this
> version to take precedence by the set_virtual_time call
> happening after the kvm_arch_set_registers, but is this
> guaranteed ?

...you might also want to look at the effects of simply
removing the KVM_REG_ARM_TIMER_CNT entry from the
'non_runtime_cpregs[]' array -- in commit 4b7a6bf402bd064
we explicitly stopped reading/writing this register's value
to/from the kernel except for inbound migration, and it
feels like this patchset is now rolling back that approach,
so maybe we should also be (configurably) rolling back some
of its implementation rather than just leaving it in place.

I note also that the commit message there had a remark
about inconsistencies between VCPUs -- is the right thing
to handle this per-VM rather than per-VCPU somehow?

thanks
-- PMM