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

KVM: PPC: Book3S HV: Introduce low level MSR accessor

kvmppc_get_msr() and kvmppc_set_msr_fast() serve as accessors for the
MSR. However because the MSR is kept in the shared regs they include a
conditional check for kvmppc_shared_big_endian() and endian conversion.

Within the Book3S HV specific code there are direct reads and writes of
shregs::msr. In preparation for Nested APIv2 these accesses need to be
replaced with accessor functions so it is possible to extend their
behavior. However, using the kvmppc_get_msr() and kvmppc_set_msr_fast()
functions is undesirable because it would introduce a conditional branch
and endian conversion that is not currently present.

kvmppc_set_msr_hv() already exists, it is used for the
kvmppc_ops::set_msr callback.

Introduce a low level accessor __kvmppc_{s,g}et_msr_hv() that simply
gets and sets shregs::msr. This will be extend for Nested APIv2 support.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230914030600.16993-8-jniethe5@gmail.com

KVM: PPC: Book3S HV: Use accessors for VCPU registers

Introduce accessor generator macros for Book3S HV VCPU registers. Use
the accessor functions to replace direct accesses to this registers.

This will be important later for Nested APIv2 support which requires
additional functionality for accessing and modifying VCPU state.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230914030600.16993-7-jniethe5@gmail.com

KVM: PPC: Book3S HV: Expose timing functions to module code

The next patch adds new timing points to the P9 entry path, some of
which are in the module code, so we need to export the timing
functions.

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220525130554.2614394-5-farosas@linux.ibm.com

KVM: PPC: Book3S HV P9: Use Linux SPR save/restore to manage some host SPRs

Linux implements SPR save/restore including storage space for registers
in the task struct for process context switching. Make use of this
similarly to the way we make use of the context switching fp/vec save
restore.

This improves code reuse, allows some stack space to be saved, and helps
with avoiding VRSAVE updates if they are not required.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-39-npiggin@gmail.com

KVM: PPC: Book3S HV P9: Move host OS save/restore functions to built-in

Move the P9 guest/host register switching functions to the built-in
P9 entry code, and export it for nested to use as well.

This allows more flexibility in scheduling these supervisor privileged
SPR accesses with the HV privileged and PR SPR accesses in the low level
entry code.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-30-npiggin@gmail.com