Re: [PATCH 1/3] KVM: PPC: Book3S: Controls for in-kernel PAPR hypercall handling

[Alexander Graf <agraf@suse.de>]

On 31.05.14 09:21, Paul Mackerras wrote:
> This provides a way for userspace controls which PAPR hcalls get
> handled in the kernel.  Each hcall can be individually enabled or
> disabled for in-kernel handling, except for H_RTAS.  The exception
> for H_RTAS is because userspace can already control whether
> individual RTAS functions are handled in-kernel or not via the
> KVM_PPC_RTAS_DEFINE_TOKEN ioctl, and because the numeric value for
> H_RTAS is out of the normal sequence of hcall numbers.
>
> Hcalls are enabled or disabled using the KVM_ENABLE_CAP ioctl for the
> KVM_CAP_PPC_ENABLE_HCALL capability on the file descriptor for the VM.
> The args field of the struct kvm_enable_cap specifies the hcall number
> in args[0] and the enable/disable flag in args[1]; 0 means disable
> in-kernel handling (so that the hcall will always cause an exit to
> userspace) and 1 means enable.  Enabling or disabling in-kernel
> handling of an hcall is effective across the whole VM.
>
> The ability for KVM_ENABLE_CAP to be used on a VM file descriptor
> on PowerPC is new, added by this commit.  The KVM_CAP_ENABLE_CAP_VM
> capability advertises that this ability exists.
>
> When a VM is created, an initial set of hcalls are enabled for
> in-kernel handling.  The set that is enabled is the set that have
> an in-kernel implementation at this point.  Any new hcall
> implementations from this point onwards should not be added to the
> default set without a good reason.
>
> No distinction is made between real-mode and virtual-mode hcall
> implementations; the one setting controls them both.
>
> Signed-off-by: Paul Mackerras <paulus@samba.org>
> ---
>   Documentation/virtual/kvm/api.txt       | 19 ++++++++++++
>   arch/powerpc/include/asm/kvm_book3s.h   |  1 +
>   arch/powerpc/include/asm/kvm_host.h     |  2 ++
>   arch/powerpc/kernel/asm-offsets.c       |  1 +
>   arch/powerpc/kvm/book3s_hv.c            | 51 +++++++++++++++++++++++++++++++++
>   arch/powerpc/kvm/book3s_hv_rmhandlers.S | 11 +++++++
>   arch/powerpc/kvm/book3s_pr.c            |  5 ++++
>   arch/powerpc/kvm/book3s_pr_papr.c       | 37 ++++++++++++++++++++++++
>   arch/powerpc/kvm/powerpc.c              | 45 +++++++++++++++++++++++++++++
>   include/uapi/linux/kvm.h                |  1 +
>   10 files changed, 173 insertions(+)
>
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 6ff3a77..73c614f 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -3002,3 +3002,22 @@ Parameters: args[0] is the XICS device fd
>               args[1] is the XICS CPU number (server ID) for this vcpu
>   
>   This capability connects the vcpu to an in-kernel XICS device.
> +
> +6.8 KVM_CAP_PPC_ENABLE_HCALL
> +
> +Architectures: ppc (VM capability)

Hrm. Just create a new section for VM scope ENABLE_CAP caps. Putting 
them into the same bucket as CPU ones will end up confusing :).

> +Parameters: args[0] is the PAPR hcall number
> +	    args[1] is 0 to disable, 1 to enable in-kernel handling
> +
> +This capability controls whether individual PAPR hypercalls (hcalls)

Sorry for not seeing this earlier. We support both ePAPR and sPAPR 
compliant hypercalls on PPC. I think it makes sense to document which 
ones we're talking about here.


Alex