[Qemu-devel] [RFC] pseries: Enable in-kernel H_LOGICAL_CI_{LOAD, STORE} implementations

[David Gibson]

qemu currently implements the hypercalls H_LOGICAL_CI_LOAD and
H_LOGICAL_CI_STORE as PAPR extensions.  These are used by the SLOF firmware
for IO, because performing cache inhibited MMIO accesses with the MMU off
(real mode) is very awkward on POWER.

This approach breaks when SLOF needs to access IO devices implemented
within KVM instead of in qemu.  The simplest example would be virtio-blk
using an iothread, because the iothread / dataplane mechanism relies on
an in-kernel implementation of the virtio queue notification MMIO.

To fix this, an in-kernel implementation of these hypercalls has been made,
however, the hypercalls still need to be enabled from qemu.  This performs
the necessary calls to do so.

Signed-off-by: David Gibson <address@hidden>
---
 hw/ppc/spapr.c       |  5 +++++
 target-ppc/kvm.c     | 27 +++++++++++++++++++++++++++
 target-ppc/kvm_ppc.h |  5 +++++
 3 files changed, 37 insertions(+)

The kernel support this qemu patch enables has been posted but not
merged as of this post.  See https://lkml.org/lkml/2015/2/3/17

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index b560459..40fe1dd 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1459,6 +1459,11 @@ static void ppc_spapr_init(MachineState *machine)
         qemu_register_reset(spapr_cpu_reset, cpu);
     }
 
+    if (kvm_enabled()) {
+        /* Enable H_LOGICAL_CI_* so SLOF can talk to in-kernel devices */
+        kvmppc_enable_logical_ci_hcalls();
+    }
+
     /* allocate RAM */
     spapr->ram_limit = ram_size;
     memory_region_allocate_system_memory(ram, NULL, "ppc_spapr.ram",
diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index 1edf2b5..c9d04e8 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -1882,6 +1882,33 @@ int kvmppc_get_hypercall(CPUPPCState *env, uint8_t *buf, 
int buf_len)
     return 0;
 }
 
+static inline int kvmppc_enable_hcall(KVMState *s, target_ulong hcall)
+{
+    return kvm_vm_enable_cap(s, KVM_CAP_PPC_ENABLE_HCALL, 0, hcall, 1);
+}
+
+void kvmppc_enable_logical_ci_hcalls(void)
+{
+    int ret1, ret2;
+
+    ret1 = kvmppc_enable_hcall(kvm_state, H_LOGICAL_CI_LOAD);
+    if (ret1 != 0) {
+        fprintf(stderr, "Warning: error enabling H_LOGICAL_CI_LOAD in KVM:"
+                " %s\n", strerror(errno));
+    }
+
+    ret2 = kvmppc_enable_hcall(kvm_state, H_LOGICAL_CI_STORE);
+    if (ret2 != 0) {
+        fprintf(stderr, "Warning: error enabling H_LOGICAL_CI_STORE in KVM:"
+                " %s\n", strerror(errno));
+     }
+
+    if ((ret1 != 0) || (ret2 != 0)) {
+        fprintf(stderr, "Warning: Couldn't enable H_LOGICAL_CI_* in KVM, SLOF"
+                " may be unable to operate devices with in-kernel 
emulation\n");
+    }
+}
+
 void kvmppc_set_papr(PowerPCCPU *cpu)
 {
     CPUState *cs = CPU(cpu);
diff --git a/target-ppc/kvm_ppc.h b/target-ppc/kvm_ppc.h
index 2e0224c..4d30e27 100644
--- a/target-ppc/kvm_ppc.h
+++ b/target-ppc/kvm_ppc.h
@@ -24,6 +24,7 @@ bool kvmppc_get_host_serial(char **buf);
 int kvmppc_get_hasidle(CPUPPCState *env);
 int kvmppc_get_hypercall(CPUPPCState *env, uint8_t *buf, int buf_len);
 int kvmppc_set_interrupt(PowerPCCPU *cpu, int irq, int level);
+void kvmppc_enable_logical_ci_hcalls(void);
 void kvmppc_set_papr(PowerPCCPU *cpu);
 int kvmppc_set_compat(PowerPCCPU *cpu, uint32_t cpu_version);
 void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int mpic_proxy);
@@ -107,6 +108,10 @@ static inline int kvmppc_set_interrupt(PowerPCCPU *cpu, 
int irq, int level)
     return -1;
 }
 
+static inline void kvmppc_enable_logical_ci_hcalls(void)
+{
+}
+
 static inline void kvmppc_set_papr(PowerPCCPU *cpu)
 {
 }
-- 
2.1.0