Re: [PATCH v3 3/3] KVM: PPC: Add KVM_CAP_PPC_AIL_MODE_3

[Fabiano Rosas <farosas@linux.ibm.com>]

Nicholas Piggin <npiggin@gmail.com> writes:

> Add KVM_CAP_PPC_AIL_MODE_3 to advertise the capability to set the AIL
> resource mode to 3 with the H_SET_MODE hypercall. This capability
> differs between processor types and KVM types (PR, HV, Nested HV), and
> affects guest-visible behaviour.
>
> QEMU will implement a cap-ail-mode-3 to control this behaviour[1], and
> use the KVM CAP if available to determine KVM support[2].
>
> [1] https://lists.nongnu.org/archive/html/qemu-ppc/2022-02/msg00437.html
> [2] https://lists.nongnu.org/archive/html/qemu-ppc/2022-02/msg00439.html
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>

> ---
>  Documentation/virt/kvm/api.rst         | 14 ++++++++++++++
>  arch/powerpc/include/asm/setup.h       |  2 ++
>  arch/powerpc/kvm/powerpc.c             | 20 ++++++++++++++++++++
>  arch/powerpc/platforms/pseries/setup.c | 12 +++++++++++-
>  include/uapi/linux/kvm.h               |  1 +
>  tools/include/uapi/linux/kvm.h         |  1 +
>  6 files changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index bb8cfddbb22d..404056a9a35a 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6995,6 +6995,20 @@ indicated by the fd to the VM this is called on.
>  This is intended to support intra-host migration of VMs between userspace VMMs,
>  upgrading the VMM process without interrupting the guest.
>
> +7.30 KVM_CAP_PPC_AIL_MODE_3
> +-------------------------------
> +
> +:Capability: KVM_CAP_PPC_AIL_MODE_3
> +:Architectures: ppc
> +:Type: vm
> +
> +This capability indicates that the kernel supports the mode 3 setting for the
> +"Address Translation Mode on Interrupt" aka "Alternate Interrupt Location"
> +resource that is controlled with the H_SET_MODE hypercall.
> +
> +This capability allows a guest kernel to use a better-performance mode for
> +handling interrupts and system calls.
> +
>  8. Other capabilities.
>  ======================
>
> diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h
> index d0d3dd531c7f..a555fb77258a 100644
> --- a/arch/powerpc/include/asm/setup.h
> +++ b/arch/powerpc/include/asm/setup.h
> @@ -28,11 +28,13 @@ void setup_panic(void);
>  #define ARCH_PANIC_TIMEOUT 180
>
>  #ifdef CONFIG_PPC_PSERIES
> +extern bool pseries_reloc_on_exception(void);
>  extern bool pseries_enable_reloc_on_exc(void);
>  extern void pseries_disable_reloc_on_exc(void);
>  extern void pseries_big_endian_exceptions(void);
>  void __init pseries_little_endian_exceptions(void);
>  #else
> +static inline bool pseries_reloc_on_exception(void) { return false; }
>  static inline bool pseries_enable_reloc_on_exc(void) { return false; }
>  static inline void pseries_disable_reloc_on_exc(void) {}
>  static inline void pseries_big_endian_exceptions(void) {}
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 2ad0ccd202d5..7dc101ea778c 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -678,6 +678,26 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		r = 1;
>  		break;
>  #endif
> +	case KVM_CAP_PPC_AIL_MODE_3:
> +		/*
> +		 * KVM PR, POWER7, and some POWER9s don't support AIL=3 mode.
> +		 * The POWER9s can support it if the guest runs in hash mode,
> +		 * but QEMU doesn't necessarily query the capability in time.
> +		 */
> +		if (hv_enabled) {
> +			if (kvmhv_on_pseries()) {
> +				if (pseries_reloc_on_exception())
> +					r = 1;
> +			} else if (cpu_has_feature(CPU_FTR_ARCH_207S) &&
> +				  !cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG)) {
> +				r = 1;
> +			} else {
> +				r = 0;
> +			}
> +		} else {
> +			r = 0;
> +		}
> +		break;
>  	default:
>  		r = 0;
>  		break;
> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
> index 83a04d967a59..182525c2abd5 100644
> --- a/arch/powerpc/platforms/pseries/setup.c
> +++ b/arch/powerpc/platforms/pseries/setup.c
> @@ -353,6 +353,13 @@ static void pseries_lpar_idle(void)
>  	pseries_idle_epilog();
>  }
>
> +static bool pseries_reloc_on_exception_enabled;
> +
> +bool pseries_reloc_on_exception(void)
> +{
> +	return pseries_reloc_on_exception_enabled;
> +}
> +
>  /*
>   * Enable relocation on during exceptions. This has partition wide scope and
>   * may take a while to complete, if it takes longer than one second we will
> @@ -377,6 +384,7 @@ bool pseries_enable_reloc_on_exc(void)
>  					" on exceptions: %ld\n", rc);
>  				return false;
>  			}
> +			pseries_reloc_on_exception_enabled = true;
>  			return true;
>  		}
>
> @@ -404,7 +412,9 @@ void pseries_disable_reloc_on_exc(void)
>  			break;
>  		mdelay(get_longbusy_msecs(rc));
>  	}
> -	if (rc != H_SUCCESS)
> +	if (rc == H_SUCCESS)
> +		pseries_reloc_on_exception_enabled = false;
> +	else
>  		pr_warn("Warning: Failed to disable relocation on exceptions: %ld\n",
>  			rc);
>  }
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 9563d294f181..65f231d048a8 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1133,6 +1133,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
>  #define KVM_CAP_VM_GPA_BITS 207
>  #define KVM_CAP_XSAVE2 208
> +#define KVM_CAP_PPC_AIL_MODE_3 209
>
>  #ifdef KVM_CAP_IRQ_ROUTING
>
> diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h
> index 9563d294f181..65f231d048a8 100644
> --- a/tools/include/uapi/linux/kvm.h
> +++ b/tools/include/uapi/linux/kvm.h
> @@ -1133,6 +1133,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
>  #define KVM_CAP_VM_GPA_BITS 207
>  #define KVM_CAP_XSAVE2 208
> +#define KVM_CAP_PPC_AIL_MODE_3 209
>
>  #ifdef KVM_CAP_IRQ_ROUTING