[RFC PATCH] KVM: arm/arm64: Don't let userspace update CNTVOFF once guest is running

Peter Maydell peter.maydell at linaro.org
Mon Jun 29 10:37:33 PDT 2015

On 29 June 2015 at 18:20, Claudio Fontana <claudio.fontana at huawei.com> wrote:
> On 26.06.2015 06:49, Jan Kiszka wrote:
>> QEMU has the concept of write-back levels: KVM_PUT_RUNTIME_STATE,
>> KVM_PUT_RESET_STATE and KVM_PUT_FULL_STATE. I suspect this registers is
>> just sorted into the wrong category, thus written as part of the
>> RUNTIME_STATE. We had such bug patterns during the x86 maturing phase as
>> well.

> It seems that QEMU target-arm ignores the level parameter to
> kvm_arch_put_registers completely.
> Is it intended?

Yes, sort of. We don't in general know anything about the semantics
of most of the system registers. It should always be safe to
read them all out of the kernel and write them back...

-- PMM

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