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>

hw/ppc/pegasos2.c

@@ -449,6 +449,11 @@ static target_ulong pegasos2_rtas(PowerPCCPU *cpu, Pegasos2MachineState *pm,
     }
 }
 
+static bool pegasos2_cpu_in_nested(PowerPCCPU *cpu)
+{
+    return false;
+}
+
 static void pegasos2_hypercall(PPCVirtualHypervisor *vhyp, PowerPCCPU *cpu)
 {
     Pegasos2MachineState *pm = PEGASOS2_MACHINE(vhyp);
@@ -504,6 +509,7 @@ static void pegasos2_machine_class_init(ObjectClass *oc, void *data)
     mc->default_ram_id = "pegasos2.ram";
     mc->default_ram_size = 512 * MiB;
 
+    vhc->cpu_in_nested = pegasos2_cpu_in_nested;
     vhc->hypercall = pegasos2_hypercall;
     vhc->cpu_exec_enter = vhyp_nop;
     vhc->cpu_exec_exit = vhyp_nop;

hw/ppc/spapr.c

@@ -4472,6 +4472,11 @@ PowerPCCPU *spapr_find_cpu(int vcpu_id)
     return NULL;
 }
 
+static bool spapr_cpu_in_nested(PowerPCCPU *cpu)
+{
+    return false;
+}
+
 static void spapr_cpu_exec_enter(PPCVirtualHypervisor *vhyp, PowerPCCPU *cpu)
 {
     SpaprCpuState *spapr_cpu = spapr_cpu_state(cpu);
@@ -4580,6 +4585,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
     fwc->get_dev_path = spapr_get_fw_dev_path;
     nc->nmi_monitor_handler = spapr_nmi;
     smc->phb_placement = spapr_phb_placement;
+    vhc->cpu_in_nested = spapr_cpu_in_nested;
     vhc->hypercall = emulate_spapr_hypercall;
     vhc->hpt_mask = spapr_hpt_mask;
     vhc->map_hptes = spapr_map_hptes;

target/ppc/cpu.h

@@ -1311,6 +1311,8 @@ PowerPCCPUClass *ppc_cpu_get_family_class(PowerPCCPUClass *pcc);
 #ifndef CONFIG_USER_ONLY
 struct PPCVirtualHypervisorClass {
     InterfaceClass parent;
+    bool (*cpu_in_nested)(PowerPCCPU *cpu);
+    void (*deliver_hv_excp)(PowerPCCPU *cpu, int excp);
     void (*hypercall)(PPCVirtualHypervisor *vhyp, PowerPCCPU *cpu);
     hwaddr (*hpt_mask)(PPCVirtualHypervisor *vhyp);
     const ppc_hash_pte64_t *(*map_hptes)(PPCVirtualHypervisor *vhyp,
@@ -1330,6 +1332,11 @@ struct PPCVirtualHypervisorClass {
 #define TYPE_PPC_VIRTUAL_HYPERVISOR "ppc-virtual-hypervisor"
 DECLARE_OBJ_CHECKERS(PPCVirtualHypervisor, PPCVirtualHypervisorClass,
                      PPC_VIRTUAL_HYPERVISOR, TYPE_PPC_VIRTUAL_HYPERVISOR)
+
+static inline bool vhyp_cpu_in_nested(PowerPCCPU *cpu)
+{
+    return PPC_VIRTUAL_HYPERVISOR_GET_CLASS(cpu->vhyp)->cpu_in_nested(cpu);
+}
 #endif /* CONFIG_USER_ONLY */
 
 void ppc_cpu_dump_state(CPUState *cpu, FILE *f, int flags);

target/ppc/excp_helper.c

@@ -1280,6 +1280,18 @@ static void powerpc_excp_booke(PowerPCCPU *cpu, int excp)
     powerpc_set_excp_state(cpu, vector, new_msr);
 }
 
+/*
+ * When running a nested HV guest under vhyp, external interrupts are
+ * delivered as HVIRT.
+ */
+static bool books_vhyp_promotes_external_to_hvirt(PowerPCCPU *cpu)
+{
+    if (cpu->vhyp) {
+        return vhyp_cpu_in_nested(cpu);
+    }
+    return false;
+}
+
 #ifdef TARGET_PPC64
 /*
  * When running under vhyp, hcalls are always intercepted and sent to the
@@ -1288,7 +1300,21 @@ static void powerpc_excp_booke(PowerPCCPU *cpu, int excp)
 static bool books_vhyp_handles_hcall(PowerPCCPU *cpu)
 {
     if (cpu->vhyp) {
-        return true;
+        return !vhyp_cpu_in_nested(cpu);
+    }
+    return false;
+}
+
+/*
+ * When running a nested KVM HV guest under vhyp, HV exceptions are not
+ * delivered to the guest (because there is no concept of HV support), but
+ * rather they are sent tothe vhyp to exit from the L2 back to the L1 and
+ * return from the H_ENTER_NESTED hypercall.
+ */
+static bool books_vhyp_handles_hv_excp(PowerPCCPU *cpu)
+{
+    if (cpu->vhyp) {
+        return vhyp_cpu_in_nested(cpu);
     }
     return false;
 }
@@ -1541,12 +1567,6 @@ static void powerpc_excp_books(PowerPCCPU *cpu, int excp)
         break;
     }
 
-    /* Sanity check */
-    if (!(env->msr_mask & MSR_HVB) && srr0 == SPR_HSRR0) {
-        cpu_abort(cs, "Trying to deliver HV exception (HSRR) %d with "
-                  "no HV support\n", excp);
-    }
-
     /*
      * Sort out endianness of interrupt, this differs depending on the
      * CPU, the HV mode, etc...
@@ -1565,10 +1585,26 @@ static void powerpc_excp_books(PowerPCCPU *cpu, int excp)
         env->spr[srr1] = msr;
     }
 
-    /* This can update new_msr and vector if AIL applies */
-    ppc_excp_apply_ail(cpu, excp, msr, &new_msr, &vector);
+    if ((new_msr & MSR_HVB) && books_vhyp_handles_hv_excp(cpu)) {
+        PPCVirtualHypervisorClass *vhc =
+            PPC_VIRTUAL_HYPERVISOR_GET_CLASS(cpu->vhyp);
+        /* Deliver interrupt to L1 by returning from the H_ENTER_NESTED call */
+        vhc->deliver_hv_excp(cpu, excp);
 
-    powerpc_set_excp_state(cpu, vector, new_msr);
+        powerpc_reset_excp_state(cpu);
+
+    } else {
+        /* Sanity check */
+        if (!(env->msr_mask & MSR_HVB) && srr0 == SPR_HSRR0) {
+            cpu_abort(cs, "Trying to deliver HV exception (HSRR) %d with "
+                      "no HV support\n", excp);
+        }
+
+        /* This can update new_msr and vector if AIL applies */
+        ppc_excp_apply_ail(cpu, excp, msr, &new_msr, &vector);
+
+        powerpc_set_excp_state(cpu, vector, new_msr);
+    }
 }
 #else
 static inline void powerpc_excp_books(PowerPCCPU *cpu, int excp)
@@ -1688,7 +1724,11 @@ static void ppc_hw_interrupt(CPUPPCState *env)
         /* HEIC blocks delivery to the hypervisor */
         if ((async_deliver && !(heic && msr_hv && !msr_pr)) ||
             (env->has_hv_mode && msr_hv == 0 && !lpes0)) {
-            powerpc_excp(cpu, POWERPC_EXCP_EXTERNAL);
+            if (books_vhyp_promotes_external_to_hvirt(cpu)) {
+                powerpc_excp(cpu, POWERPC_EXCP_HVIRT);
+            } else {
+                powerpc_excp(cpu, POWERPC_EXCP_EXTERNAL);
+            }
             return;
         }
     }
@@ -1798,6 +1838,8 @@ void ppc_cpu_do_fwnmi_machine_check(CPUState *cs, target_ulong vector)
         msr |= (1ULL << MSR_LE);
     }
 
+    /* Anything for nested required here? MSR[HV] bit? */
+
     powerpc_set_excp_state(cpu, vector, msr);
 }
 

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;
 }