Hi Amit. Thanks for the patch and incorporating V3 review comments. Further review comments inline below:
Amit Machhiwal <[email protected]> writes: > On POWER systems, the host CPU may run in a compatibility mode (e.g., a > Power11 processor operating in Power10 compatibility mode). In such > cases, the effective CPU level exposed to guests differs from the > physical processor generation. > > When running nested KVM guests, QEMU derives the host CPU type using > mfpvr(), which reflects the physical processor version. This can result > in a mismatch between the CPU model selected by QEMU and the > compatibility mode enforced by the host, leading to guest boot failures. > > For example, booting a nested guest on a Power11 LPAR configured in > Power10 compatibility mode fails with: > > KVM-NESTEDv2: couldn't set guest wide elements > [..KVM reg dump..] > > This occurs because QEMU selects a CPU model corresponding to the > physical processor (via mfpvr()), while the host operates in a lower > compatibility mode. As a result, KVM rejects the requested compatibility > level during guest initialization. > > Add support for retrieving host CPU compatibility capabilities for > nested guests on PowerVM (PAPR nested API v2). The hypervisor provides > the effective compatibility levels via the H_GUEST_GET_CAPABILITIES > hcall, which reflects the processor modes negotiated between the Power > hypervisor (L0) and the host partition (L1). > > On pseries systems, obtain the capability bitmap using > plpar_guest_get_capabilities() and return it via struct > kvm_ppc_compat_caps. The implementation defines KVM-specific capability > constants (KVM_PPC_COMPAT_CAP_POWER9/10/11) and applies masking to ensure > only supported processor modes are exposed to userspace. This information > is then exposed through the KVM_PPC_GET_COMPAT_CAPS ioctl. > > Hook the implementation into the Book3S HV kvmppc_ops so that it can be > invoked by the generic KVM ioctl handling code. > > Suggested-by: Vaibhav Jain <[email protected]> > Signed-off-by: Amit Machhiwal <[email protected]> > --- > arch/powerpc/include/uapi/asm/kvm.h | 11 ++++++++++- > arch/powerpc/kvm/book3s_hv.c | 17 +++++++++++++++++ > 2 files changed, 27 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/uapi/asm/kvm.h > b/arch/powerpc/include/uapi/asm/kvm.h > index 8a38be6c3b03..730488681443 100644 > --- a/arch/powerpc/include/uapi/asm/kvm.h > +++ b/arch/powerpc/include/uapi/asm/kvm.h > @@ -443,7 +443,16 @@ struct kvm_ppc_compat_caps { > __u64 size; /* Size of this structure */ > __u64 compat_capabilities; /* Capabilities supported by the host */ > }; > - > +/* > + * Capability bits for compat_capabilities field in kvm_ppc_compat_caps. > + * These bits indicate which processor compatibility modes are supported. > + */ > +#define KVM_PPC_COMPAT_CAP_POWER9 (1ULL << 62) > +#define KVM_PPC_COMPAT_CAP_POWER10 (1ULL << 61) > +#define KVM_PPC_COMPAT_CAP_POWER11 (1ULL << 60) > +#define KVM_PPC_COMPAT_BITMASK (KVM_PPC_COMPAT_CAP_POWER9 | \ > + KVM_PPC_COMPAT_CAP_POWER10 | \ > + KVM_PPC_COMPAT_CAP_POWER11) > /* > * Values for character and character_mask. > * These are identical to the values used by H_GET_CPU_CHARACTERISTICS. > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c > index f9380ef65750..f674386df62c 100644 > --- a/arch/powerpc/kvm/book3s_hv.c > +++ b/arch/powerpc/kvm/book3s_hv.c > @@ -6523,6 +6523,22 @@ 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()) > + rc = plpar_guest_get_capabilities(0, > &capabilities); I think instead of making the hcall you should use the 'nested_capabilities' extern symbol as it would already the same value. This symbol is already accessible in 'book3s_hv.c' > + host_caps->compat_capabilities = capabilities & > + KVM_PPC_COMPAT_BITMASK; > + } > + > + return rc; > +} > + > static struct kvmppc_ops kvm_ops_hv = { > .get_sregs = kvm_arch_vcpu_ioctl_get_sregs_hv, > .set_sregs = kvm_arch_vcpu_ioctl_set_sregs_hv, > @@ -6565,6 +6581,7 @@ static struct kvmppc_ops kvm_ops_hv = { > .hash_v3_possible = kvmppc_hash_v3_possible, > .create_vcpu_debugfs = kvmppc_arch_create_vcpu_debugfs_hv, > .create_vm_debugfs = kvmppc_arch_create_vm_debugfs_hv, > + .get_compat_caps = kvmppc_get_compat_caps, > }; > > static int kvm_init_subcore_bitmap(void) > -- > 2.50.1 (Apple Git-155) > > -- Cheers ~ Vaibhav
