Re: [Qemu-devel] [PATCH] spapr: reset @kvm_vcpu_dirty before starting CPU

["Andreas Färber" <afaerber@suse.de>]

Am 15.01.2014 05:57, schrieb Alexey Kardashevskiy:
> Normally QEMU kvm_arch_get_registers() reads registers and sets a dirty
> flag which prevents further registers reading from KVM till
> kvm_arch_put_registers() executes and resets the flag.
> 
> However if we run QEMU with "-S" ("suspended"), then execute "info cpus"
> from the QEMU monitor, we end up with not reading registers in
> rtas_start_cpu() as qmp_query_cpus() calls kvm_cpu_synchronize_state()
> which leaves @kvm_vcpu_dirty=true what prevents kvm_cpu_synchronize_state()
> from synchronizing registers and we loose the values.
> 
> This resets @kvm_vcpu_dirty flag as we do not have content which we really want to
> keep at this point as the CPU is halted.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> 
> We could also reset @kvm_vcpu_dirty in qmp_query_cpus() but that would be
> racy.
> ---
>  hw/ppc/spapr_rtas.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index 1cb276d..3dade5e 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -185,6 +185,8 @@ static void rtas_start_cpu(PowerPCCPU *cpu_, sPAPREnvironment *spapr,
>          /* This will make sure qemu state is up to date with kvm, and
>           * mark it dirty so our changes get flushed back before the
>           * new cpu enters */
> +
> +        cs->kvm_vcpu_dirty = false;
>          kvm_cpu_synchronize_state(cs);

While I am not familiar with whether or not the dirty flag should be
changed, I've noticed in the past that sPAPR is the only user of
kvm_cpu_synchronize_state() outside of KVM code IIUC. Would be nice if
you could replace that with cpu_synchronize_state() in its own patch
when you find some time.

Regards,
Andreas

>  
>          env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
> 


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