[1/3] KVM: PPC: Add generic single register ioctls

Right now we transfer a static struct every time we want to get or set
registers. Unfortunately, over time we realize that there are more of
these than we thought of before and the extensibility and flexibility of
transferring a full struct every time is limited.

So this is a new approach to the problem. With these new ioctls, we can
get and set a single register that is identified by an ID. This allows for
very precise and limited transmittal of data. When we later realize that
it's a better idea to shove over multiple registers at once, we can reuse
most of the infrastructure and simply implement a GET_MANY_REGS / SET_MANY_REGS
interface.

The only downpoint I see to this one is that it needs to pad to 1024 bits
(hardware is already on 512 bit registers, so I wanted to leave some room)
which is slightly too much for transmitting only 64 bits. But if that's all
the tradeoff we have to do for getting an extensible interface, I'd say go
for it nevertheless.

Signed-off-by: Alexander Graf <agraf@suse.de>

---

v1 -> v2:

  - rename KVM_ONE_REG to KVM_REG
  - change semantics to include size in constant
    and a user pointer to write/read to/from
  - update documentation respectively
---
 Documentation/virtual/kvm/api.txt |   40 +++++++++++++++++++++++++++++
 arch/powerpc/kvm/powerpc.c        |   51 +++++++++++++++++++++++++++++++++++++
 include/linux/kvm.h               |   35 +++++++++++++++++++++++++
 3 files changed, 126 insertions(+), 0 deletions(-)

On 06.01.2012, at 04:59, Alexander Graf wrote:

> Right now we transfer a static struct every time we want to get or set
> registers. Unfortunately, over time we realize that there are more of
> these than we thought of before and the extensibility and flexibility of
> transferring a full struct every time is limited.
> 
> So this is a new approach to the problem. With these new ioctls, we can
> get and set a single register that is identified by an ID. This allows for
> very precise and limited transmittal of data. When we later realize that
> it's a better idea to shove over multiple registers at once, we can reuse
> most of the infrastructure and simply implement a GET_MANY_REGS / SET_MANY_REGS
> interface.
> 
> The only downpoint I see to this one is that it needs to pad to 1024 bits
> (hardware is already on 512 bit registers, so I wanted to leave some room)
> which is slightly too much for transmitting only 64 bits. But if that's all
> the tradeoff we have to do for getting an extensible interface, I'd say go
> for it nevertheless.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> 
> ---
> 
> v1 -> v2:
> 
>  - rename KVM_ONE_REG to KVM_REG
>  - change semantics to include size in constant
>    and a user pointer to write/read to/from
>  - update documentation respectively
> ---
> Documentation/virtual/kvm/api.txt |   40 +++++++++++++++++++++++++++++
> arch/powerpc/kvm/powerpc.c        |   51 +++++++++++++++++++++++++++++++++++++
> include/linux/kvm.h               |   35 +++++++++++++++++++++++++
> 3 files changed, 126 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index a4d7b4d..8494214 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1523,6 +1523,46 @@ following algorithm:
> Some guests configure the LINT1 NMI input to cause a panic, aiding in
> debugging.
> 
> +4.65 KVM_SET_ONE_REG
> +
> +Capability: KVM_CAP_ONE_REG
> +Architectures: all
> +Type: vcpu ioctl
> +Parameters: struct kvm_one_reg (in)
> +Returns: 0 on success, negative value on failure
> +
> +struct kvm_one_reg {
> +       __u64 id;
> +       __u64 addr;
> +};
> +
> +Using this ioctl, a single vcpu register can be set to a specific value
> +defined by user space with the passed in struct kvm_one_reg, where id
> +refers to the register identifier as described below and addr is a pointer
> +to a variable with the respective size. There can be architecture agnostic
> +and architecture specific registers. Each have their own range of operation
> +and their own constants and width. To keep track of the implemented
> +registers, find a list below:
> +
> +  Arch  |       Register        | Width (bits)
> +        |                       |
> +
> +4.66 KVM_GET_ONE_REG
> +
> +Capability: KVM_CAP_ONE_REG
> +Architectures: all
> +Type: vcpu ioctl
> +Parameters: struct kvm_one_reg (in and out)
> +Returns: 0 on success, negative value on failure
> +
> +This ioctl allows to receive the value of a single register implemented
> +in a vcpu. The register to read is indicated by the "id" field of the
> +kvm_one_reg struct passed in. On success, the register value can be found
> +at the memory location pointed to by "addr".
> +
> +The list of registers accessible using this interface is identical to the
> +list in 4.64.
> +
> 5. The kvm_run structure
> 
> Application code obtains a pointer to the kvm_run structure by
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 76993eb..9c598b6 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -214,6 +214,7 @@ int kvm_dev_ioctl_check_extension(long ext)
> 	case KVM_CAP_PPC_UNSET_IRQ:
> 	case KVM_CAP_PPC_IRQ_LEVEL:
> 	case KVM_CAP_ENABLE_CAP:
> +	case KVM_CAP_ONE_REG:
> 		r = 1;
> 		break;
> #ifndef CONFIG_KVM_BOOK3S_64_HV
> @@ -642,6 +643,32 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
> 	return r;
> }
> 
> +static int kvm_vcpu_ioctl_get_one_reg(struct kvm_vcpu *vcpu,
> +				      struct kvm_one_reg *reg)
> +{
> +	int r = -EINVAL;
> +
> +	switch (reg->id) {
> +	default:
> +		break;
> +	}
> +
> +	return r;
> +}
> +
> +static int kvm_vcpu_ioctl_set_one_reg(struct kvm_vcpu *vcpu,
> +				      struct kvm_one_reg *reg)
> +{
> +	int r = -EINVAL;
> +
> +	switch (reg->id) {
> +	default:
> +		break;
> +	}
> +
> +	return r;
> +}
> +
> int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
>                                     struct kvm_mp_state *mp_state)
> {
> @@ -681,6 +708,30 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> 		break;
> 	}
> 
> +	case KVM_GET_ONE_REG:
> +	{
> +		struct kvm_one_reg reg;
> +		r = -EFAULT;
> +		if (copy_from_user(&reg, argp, sizeof(reg)))
> +			goto out;
> +		r = kvm_vcpu_ioctl_get_one_reg(vcpu, &reg);
> +		if (copy_to_user(argp, &reg, sizeof(reg))) {
> +			r = -EFAULT;
> +			goto out;
> +		}

This is useless now - we already do the write to the user defined address. No need to write back the address and id fields :). Will send out v3 soon.


Alex

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