Re: [PATCHv3 5/7] KVM: PPC: Book3S HV nestedv2: reject vCPU ids beyond the PAPR limit

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] KVM: PPC: undeclared KVM_MAX_VCPU_IDS_NESTEDv2 in kvm_arch_vcpu_precreate()
--

commit 6b87f3d0f26a22dc1fab90af1a0540a7a33c6a90
Author: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

KVM: PPC: Book3S HV nestedv2: reject vCPU ids beyond the PAPR limit

This commit adds a check in kvm_arch_vcpu_precreate() to reject vCPU IDs at
or above KVM_MAX_VCPU_IDS_NESTEDv2 with -EINVAL when running on nestedv2,
avoiding failing later in H_GUEST_CREATE_VCPU.

> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 9194cf492d1ca..f82d3545b39ad 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -772,6 +772,9 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
>  
>  int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id)
>  {
> +	if (kvmhv_is_nestedv2() && id >= KVM_MAX_VCPU_IDS_NESTEDv2)
> +		return -EINVAL;

[Severity: Medium]
Is this commit missing the prerequisite patch referenced in the commit
message?

In arch/powerpc/kvm/powerpc.c, kvm_arch_vcpu_precreate() checks id against
KVM_MAX_VCPU_IDS_NESTEDv2, but KVM_MAX_VCPU_IDS_NESTEDv2 is not defined in
arch/powerpc/include/asm/kvm_host.h:

#define KVM_MAX_VCPU_IDS	(MAX_SMT_THREADS * KVM_MAX_VCORES)

or anywhere else in the tree, causing compilation of
arch/powerpc/kvm/powerpc.c to fail when CONFIG_KVM is enabled.

In addition, the commit message notes that the previous patch caps
KVM_CAP_MAX_VCPU_ID at 2048 on nestedv2, yet kvm_vm_ioctl_check_extension()
in arch/powerpc/kvm/powerpc.c still returns KVM_MAX_VCPU_IDS unconditionally:

	case KVM_CAP_MAX_VCPU_ID:
		r = KVM_MAX_VCPU_IDS;
		break;

Should the prerequisite patch defining KVM_MAX_VCPU_IDS_NESTEDv2 and capping
KVM_CAP_MAX_VCPU_ID in kvm_vm_ioctl_check_extension() be applied before this
change?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/3b233fa135d54d3ffb569d7febdc1cb8e0ed406a.1793546707.git.ritesh.list@gmail.com?part=1