Re: [PATCH v9 2/4] KVM: PPC: Book3S HV: Implement compat CPU capability retrieval for KVM on PowerVM

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] KVM_CAP_PPC_COMPAT_CAPS advertises capability support on all pseries hosts, but the KVM_PPC_GET_COMPAT_CAPS ioctl fails with -EINVAL on non-nestedv2 pseries hosts.
--

--- Patch [2]: [PATCH v9 2/4] KVM: PPC: Book3S HV: Implement compat CPU capability retrieval for KVM on PowerVM ---
commit 48012da6c0966da1bf70f356cb9a87c22af64308
Author: Amit Machhiwal <[email protected]>

KVM: PPC: Book3S HV: Implement compat CPU capability retrieval for KVM on PowerVM

This commit adds support for retrieving host CPU compatibility capabilities 
for nested guests on PowerVM via a new ioctl, KVM_PPC_GET_COMPAT_CAPS. It 
retrieves the cached capabilities negotiated via the H_GUEST_GET_CAPABILITIES 
hcall for nestedv2 systems.

> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 61dbeea317f3b..8799124b80960 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c

[ ... ]

> @@ -6510,6 +6510,25 @@ static bool kvmppc_hash_v3_possible(void)
>  	return true;
>  }
>  
> +
> +static int kvmppc_get_compat_caps(struct kvm_ppc_compat_caps *host_caps)
> +{
> +	unsigned long capabilities = 0;
> +	long rc = -EINVAL;
> +
> +	if (kvmhv_on_pseries()) {
> +		if (kvmhv_is_nestedv2()) {
> +			WARN_ON_ONCE(!nested_capabilities);
> +			capabilities = nested_capabilities;
> +			rc = 0;
> +		}
> +	}
> +

[Severity: High]
KVM_CAP_PPC_COMPAT_CAPS appears to be advertised for all pseries hosts in
kvm_vm_ioctl_check_extension():

	case KVM_CAP_PPC_COMPAT_CAPS:
		r = 0;
		if (hv_enabled && kvmhv_on_pseries())
			r = 1;
		break;

But here in kvmppc_get_compat_caps(), the ioctl returns -EINVAL for 
non-nestedv2 pseries hosts.

Will this mismatch cause userspace (like QEMU) to fail during guest 
initialization if it sees the capability is supported on a non-nestedv2 
host, but the ioctl unexpectedly fails with -EINVAL?

> +	host_caps->compat_capabilities = capabilities & KVM_PPC_COMPAT_BITMASK;
> +
> +	return rc;
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=2