KVM: PPC: Book3S HV: Fix L2 guest reboot failure due to empty 'arch_compat'

Currently, rebooting a pseries nested qemu-kvm guest (L2) results in
below error as L1 qemu sends PVR value 'arch_compat' == 0 via
ppc_set_compat ioctl. This triggers a condition failure in
kvmppc_set_arch_compat() resulting in an EINVAL.

qemu-system-ppc64: Unable to set CPU compatibility mode in KVM: Invalid
argument

Also, a value of 0 for arch_compat generally refers the default
compatibility of the host. But, arch_compat, being a Guest Wide Element
in nested API v2, cannot be set to 0 in GSB as PowerVM (L0) expects a
non-zero value. A value of 0 triggers a kernel trap during a reboot and
consequently causes it to fail:

[ 22.106360] reboot: Restarting system
KVM: unknown exit, hardware reason ffffffffffffffea
NIP 0000000000000100 LR 000000000000fe44 CTR 0000000000000000 XER 0000000020040092 CPU#0
MSR 0000000000001000 HID0 0000000000000000 HF 6c000000 iidx 3 didx 3
TB 00000000 00000000 DECR 0
GPR00 0000000000000000 0000000000000000 c000000002a8c300 000000007fe00000
GPR04 0000000000000000 0000000000000000 0000000000001002 8000000002803033
GPR08 000000000a000000 0000000000000000 0000000000000004 000000002fff0000
GPR12 0000000000000000 c000000002e10000 0000000105639200 0000000000000004
GPR16 0000000000000000 000000010563a090 0000000000000000 0000000000000000
GPR20 0000000105639e20 00000001056399c8 00007fffe54abab0 0000000105639288
GPR24 0000000000000000 0000000000000001 0000000000000001 0000000000000000
GPR28 0000000000000000 0000000000000000 c000000002b30840 0000000000000000
CR 00000000 [ - - - - - - - - ] RES 000@ffffffffffffffff
SRR0 0000000000000000 SRR1 0000000000000000 PVR 0000000000800200 VRSAVE 0000000000000000
SPRG0 0000000000000000 SPRG1 0000000000000000 SPRG2 0000000000000000 SPRG3 0000000000000000
SPRG4 0000000000000000 SPRG5 0000000000000000 SPRG6 0000000000000000 SPRG7 0000000000000000
HSRR0 0000000000000000 HSRR1 0000000000000000
CFAR 0000000000000000
LPCR 0000000000020400
PTCR 0000000000000000 DAR 0000000000000000 DSISR 0000000000000000

kernel:trap=0xffffffea | pc=0x100 | msr=0x1000

This patch updates kvmppc_set_arch_compat() to use the host PVR value if
'compat_pvr' == 0 indicating that qemu doesn't want to enforce any
specific PVR compat mode.

The relevant part of the code might need a rework if PowerVM implements
a support for `arch_compat == 0` in nestedv2 API.

Fixes: 19d31c5f1157 ("KVM: PPC: Add support for nestedv2 guests")
Reviewed-by: "Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org>
Reviewed-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240207054526.3720087-1-amachhiw@linux.ibm.com

KVM: PPC: Book3S HV nestedv2: Register the VPA with the L0

In the nestedv2 case, the L1 may register the L2's VPA with the L0. This
allows the L0 to manage the L2's dispatch count, as well as enable
possible performance optimisations by seeing if certain resources are
not being used by the L2 (such as the PMCs).

Use the H_GUEST_SET_STATE call to inform the L0 of the L2's VPA
address. This can not be done in the H_GUEST_VCPU_RUN input buffer.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231201132618.555031-11-vaibhav@linux.ibm.com

KVM: PPC: Add support for nestedv2 guests

A series of hcalls have been added to the PAPR which allow a regular
guest partition to create and manage guest partitions of its own. KVM
already had an interface that allowed this on powernv platforms. This
existing interface will now be called "nestedv1". The newly added PAPR
interface will be called "nestedv2". PHYP will support the nestedv2
interface. At this time the host side of the nestedv2 interface has not
been implemented on powernv but there is no technical reason why it
could not be added.

The nestedv1 interface is still supported.

Add support to KVM to utilize these hcalls to enable running nested
guests as a pseries guest on PHYP.

Overview of the new hcall usage:

- L1 and L0 negotiate capabilities with
H_GUEST_{G,S}ET_CAPABILITIES()

- L1 requests the L0 create a L2 with
H_GUEST_CREATE() and receives a handle to use in future hcalls

- L1 requests the L0 create a L2 vCPU with
H_GUEST_CREATE_VCPU()

- L1 sets up the L2 using H_GUEST_SET and the
H_GUEST_VCPU_RUN input buffer

- L1 requests the L0 runs the L2 vCPU using H_GUEST_VCPU_RUN()

- L2 returns to L1 with an exit reason and L1 reads the
H_GUEST_VCPU_RUN output buffer populated by the L0

- L1 handles the exit using H_GET_STATE if necessary

- L1 reruns L2 vCPU with H_GUEST_VCPU_RUN

- L1 frees the L2 in the L0 with H_GUEST_DELETE()

Support for the new API is determined by trying
H_GUEST_GET_CAPABILITIES. On a successful return, use the nestedv2
interface.

Use the vcpu register state setters for tracking modified guest state
elements and copy the thread wide values into the H_GUEST_VCPU_RUN input
buffer immediately before running a L2. The guest wide
elements can not be added to the input buffer so send them with a
separate H_GUEST_SET call if necessary.

Make the vcpu register getter load the corresponding value from the real
host with H_GUEST_GET. To avoid unnecessarily calling H_GUEST_GET, track
which values have already been loaded between H_GUEST_VCPU_RUN calls. If
an element is present in the H_GUEST_VCPU_RUN output buffer it also does
not need to be loaded again.

Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Signed-off-by: Gautam Menghani <gautam@linux.ibm.com>
Signed-off-by: Kautuk Consul <kconsul@linux.vnet.ibm.com>
Signed-off-by: Amit Machhiwal <amachhiw@linux.vnet.ibm.com>
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230914030600.16993-11-jniethe5@gmail.com