Subject: Re: [PATCH] powerpc/kvmbook3s_hv: propagate H_SET_MODE to the host

From: Paul Mackerras <[email-masked]>
Date: Thu, 26 Sep 2013 08:31:18 +1000

On Wed, Sep 25, 2013 at 02:10:27PM +0200, Laurent Dufour wrote:
> Follow-up to Anton's H_SET_MODE patch, the host should be taken aware of
> guest endianess change.
> 
> The hcall H_SET_MODE is processed in kvm then in the host.
> 
> Signed-off-by: Laurent Dufour <[email-masked]>
> ---
>  arch/powerpc/kvm/book3s_hv.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 998cad3..4a47c74 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -599,6 +599,14 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
>  					kvmppc_get_gpr(vcpu, 5),
>  					kvmppc_get_gpr(vcpu, 6),
>  					kvmppc_get_gpr(vcpu, 7));
> +		/*
> +		 * If the hcall succeeded, we propagate it to the host.
> +		 * This way, it will be aware of the endianess's change too.
> +		 * The assumption is made that the hcall will succeed in the
> +		 * host.
> +		 */
> +		if (ret == H_SUCCESS)
> +			return RESUME_HOST;
>  		break;

The problem with this is that H_SET_MODE isn't just used for setting
endianness; it also does breakpoint setting (DAWR/X and CIABR), which
might happen very frequently, so we don't want them being punted up to
userspace.

Paul.