target/ppc: Implement large decrementer support for KVM

Implement support to allow KVM guests to take advantage of the large
decrementer introduced on POWER9 cpus.

To determine if the host can support the requested large decrementer
size, we check it matches that specified in the ibm,dec-bits device-tree
property. We also need to enable it in KVM by setting the LPCR_LD bit in
the LPCR. Note that to do this we need to try and set the bit, then read
it back to check the host allowed us to set it, if so we can use it but
if we were unable to set it the host cannot support it and we must not
use the large decrementer.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20190301024317.22137-3-sjitindarsingh@gmail.com>
[dwg: Small style fixes]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 19 insertions, 3 deletions

diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 6d6dca30db..942ac8ebbe 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -394,6 +394,7 @@ static void cap_large_decr_apply(sPAPRMachineState *spapr,
                                  uint8_t val, Error **errp)
 {
     PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
+    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
 
     if (!val) {
         return; /* Disabled by default */
@@ -406,9 +407,17 @@ static void cap_large_decr_apply(sPAPRMachineState *spapr,
                 "Large decrementer only supported on POWER9, try -cpu POWER9");
             return;
         }
-    } else {
-        error_setg(errp,
-                   "No large decrementer support, try cap-large-decr=off");
+    } else if (kvm_enabled()) {
+        int kvm_nr_bits = kvmppc_get_cap_large_decr();
+
+        if (!kvm_nr_bits) {
+            error_setg(errp,
+                       "No large decrementer support, try cap-large-decr=off");
+        } else if (pcc->lrg_decr_bits != kvm_nr_bits) {
+            error_setg(errp,
+"KVM large decrementer size (%d) differs to model (%d), try -cap-large-decr=off",
+                kvm_nr_bits, pcc->lrg_decr_bits);
+        }
     }
 }
 
@@ -419,6 +428,13 @@ static void cap_large_decr_cpu_apply(sPAPRMachineState *spapr,
     CPUPPCState *env = &cpu->env;
     target_ulong lpcr = env->spr[SPR_LPCR];
 
+    if (kvm_enabled()) {
+        if (kvmppc_enable_cap_large_decr(cpu, val)) {
+            error_setg(errp,
+                       "No large decrementer support, try cap-large-decr=off");
+        }
+    }
+
     if (val) {
         lpcr |= LPCR_LD;
     } else {