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

[Alexander Graf]

On 15.01.2014, at 05:57, Alexey Kardashevskiy <address@hidden> wrote:

> 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.

But that's fine because the values are already synchronized and couldn't have 
changed because the guest cpu wasn't running, no?


Alex

> 
> 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 <address@hidden>
> ---
> 
> 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);
> 
>         env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
> -- 
> 1.8.4.rc4
>