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@xxxxxxx>
>
> ---
>
> 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(®, argp, sizeof(reg)))
> + goto out;
> + r = kvm_vcpu_ioctl_get_one_reg(vcpu, ®);
> + if (copy_to_user(argp, ®, 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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