target/ppc: Introduce a vhyp framework for nested HV support

Introduce virtual hypervisor methods that can support a "Nested KVM HV"
implementation using the bare metal 2-level radix MMU, and using HV
exceptions to return from H_ENTER_NESTED (rather than cause interrupts).

HV exceptions can now be raised in the TCG spapr machine when running a
nested KVM HV guest. The main ones are the lev==1 syscall, the hdecr,
hdsi and hisi, hv fu, and hv emu, and h_virt external interrupts.

HV exceptions are intercepted in the exception handler code and instead
of causing interrupts in the guest and switching the machine to HV mode,
they go to the vhyp where it may exit the H_ENTER_NESTED hcall with the
interrupt vector numer as return value as required by the hcall API.

Address translation is provided by the 2-level page table walker that is
implemented for the bare metal radix MMU. The partition scope page table
is pointed to the L1's partition scope by the get_pate vhc method.

Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20220216102545.1808018-9-npiggin@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/target/ppc/mmu-radix64.c b/target/ppc/mmu-radix64.c
index 9c557c6de9..67c38f065b 100644
--- a/target/ppc/mmu-radix64.c
+++ b/target/ppc/mmu-radix64.c
@@ -355,12 +355,19 @@ static int ppc_radix64_partition_scoped_xlate(PowerPCCPU *cpu,
 }
 
 /*
- * The spapr vhc has a flat partition scope provided by qemu memory.
+ * The spapr vhc has a flat partition scope provided by qemu memory when
+ * not nested.
+ *
+ * When running a nested guest, the addressing is 2-level radix on top of the
+ * vhc memory, so it works practically identically to the bare metal 2-level
+ * radix. So that code is selected directly. A cleaner and more flexible nested
+ * hypervisor implementation would allow the vhc to provide a ->nested_xlate()
+ * function but that is not required for the moment.
  */
 static bool vhyp_flat_addressing(PowerPCCPU *cpu)
 {
     if (cpu->vhyp) {
-        return true;
+        return !vhyp_cpu_in_nested(cpu);
     }
     return false;
 }