Re: [PATCH 8/9] RISC-V: KVM: Add ONE_REG interface for mvendorid, marchid, and mimpid

Andrew Jones
2022-11-29T05:46:59Z

On Mon, Nov 28, 2022 at 09:44:23PM +0530, Anup Patel wrote:
> We add ONE_REG interface for VCPU mvendorid, marchid, and mimpid
> so that KVM user-space can change this details to support migration
> across heterogeneous hosts.
>
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> ---
> arch/riscv/include/uapi/asm/kvm.h | 3 +++
> arch/riscv/kvm/vcpu.c | 27 +++++++++++++++++++++++++++
> 2 files changed, 30 insertions(+)
>
> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index 8985ff234c01..92af6f3f057c 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -49,6 +49,9 @@ struct kvm_sregs {
> struct kvm_riscv_config {
> unsigned long isa;
> unsigned long zicbom_block_size;
> + unsigned long mvendorid;
> + unsigned long marchid;
> + unsigned long mimpid;
> };
>
> /* CORE registers for KVM_GET_ONE_REG and KVM_SET_ONE_REG */
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 312a8a926867..7c08567097f0 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -276,6 +276,15 @@ static int kvm_riscv_vcpu_get_reg_config(struct kvm_vcpu *vcpu,
> return -EINVAL;
> reg_val = riscv_cbom_block_size;
> break;
> + case KVM_REG_RISCV_CONFIG_REG(mvendorid):
> + reg_val = vcpu->arch.mvendorid;
> + break;
> + case KVM_REG_RISCV_CONFIG_REG(marchid):
> + reg_val = vcpu->arch.marchid;
> + break;
> + case KVM_REG_RISCV_CONFIG_REG(mimpid):
> + reg_val = vcpu->arch.mimpid;
> + break;
> default:
> return -EINVAL;
> }
> @@ -338,6 +347,24 @@ static int kvm_riscv_vcpu_set_reg_config(struct kvm_vcpu *vcpu,
> break;
> case KVM_REG_RISCV_CONFIG_REG(zicbom_block_size):
> return -EOPNOTSUPP;
> + case KVM_REG_RISCV_CONFIG_REG(mvendorid):
> + if (!vcpu->arch.ran_atleast_once)
> + vcpu->arch.mvendorid = reg_val;
> + else
> + return -EBUSY;
> + break;
> + case KVM_REG_RISCV_CONFIG_REG(marchid):
> + if (!vcpu->arch.ran_atleast_once)
> + vcpu->arch.marchid = reg_val;
> + else
> + return -EBUSY;
> + break;
> + case KVM_REG_RISCV_CONFIG_REG(mimpid):
> + if (!vcpu->arch.ran_atleast_once)
> + vcpu->arch.mimpid = reg_val;
> + else
> + return -EBUSY;
> + break;
> default:
> return -EINVAL;
> }
> --
> 2.34.1
>

At some point we should patch Documentation/virt/kvm/api.rst to describe
the possible errors we have. It's missing EOPNOTSUPP and EBUSY.

Also, I see a couple places were we use EOPNOTSUPP that would be better
as EBUSY. And finally I wonder if we shouldn't use ENOENT when the reg_num
is wrong/unknown, which would allow us to differentiate between bad
reg_num and bad reg_val in set-one ioctls.

I can send an RFC series to better describe these thoughts.

And for this patch,

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Thanks,
drew