[Qemu-devel] [PATCH 2/4] ppc: First cut implementation of -cpu host

[David Gibson]

For convenience with kvm, x86 allows the user to specify -cpu host on the
qemu command line, which means make the guest cpu the same as the host
cpu.  This patch implements the same option for ppc targets.

For now, this just read the host PVR (Processor Version Register) and
selects one of our existing CPU specs based on it.  This means that the
option will not work if the host cpu is not supported by TCG, even if that
wouldn't matter for use under kvm.

In future, we can extend this in future to override parts of the cpu spec
based on information obtained from the host (via /proc/cpuinfo, the host
device tree, or explicit KVM calls).  That will let us handle cases where
the real kvm-virtualized CPU doesn't behave exactly like the TCG-emulated
CPU.  With appropriate annotation of the CPU specs we'll also then be able
to use host cpus under kvm even when there isn't a matching full TCG model.

Signed-off-by: David Gibson <address@hidden>
---
 target-ppc/cpu.h            |    1 +
 target-ppc/kvm.c            |   19 +++++++++++++++++++
 target-ppc/kvm_ppc.h        |    6 ++++++
 target-ppc/translate_init.c |    8 +++++++-
 4 files changed, 33 insertions(+), 1 deletions(-)

diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
index 3f77e30..8e5c85c 100644
--- a/target-ppc/cpu.h
+++ b/target-ppc/cpu.h
@@ -1107,6 +1107,7 @@ void ppc_store_msr (CPUPPCState *env, target_ulong value);
 
 void ppc_cpu_list (FILE *f, fprintf_function cpu_fprintf);
 
+const ppc_def_t *ppc_find_by_pvr(uint32_t pvr);
 const ppc_def_t *cpu_ppc_find_by_name (const char *name);
 int cpu_ppc_register_internal (CPUPPCState *env, const ppc_def_t *def);
 
diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index 6a48eb4..430558b 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -878,6 +878,25 @@ int kvmppc_remove_spapr_tce(void *table, int fd, uint32_t 
window_size)
     return 0;
 }
 
+static inline uint32_t mfpvr(void)
+{
+    uint32_t pvr;
+
+    asm ("mfpvr %0"
+         : "=r"(pvr));
+    return pvr;
+}
+
+const ppc_def_t *kvmppc_host_cpu_def(void)
+{
+    uint32_t host_pvr = mfpvr();
+    const ppc_def_t *base_spec;
+
+    base_spec = ppc_find_by_pvr(host_pvr);
+
+    return base_spec;
+}
+
 bool kvm_arch_stop_on_emulation_error(CPUState *env)
 {
     return true;
diff --git a/target-ppc/kvm_ppc.h b/target-ppc/kvm_ppc.h
index fa131bf..0062906 100644
--- a/target-ppc/kvm_ppc.h
+++ b/target-ppc/kvm_ppc.h
@@ -24,6 +24,7 @@ int kvmppc_smt_threads(void);
 off_t kvmppc_alloc_rma(const char *name);
 void *kvmppc_create_spapr_tce(uint32_t liobn, uint32_t window_size, int *pfd);
 int kvmppc_remove_spapr_tce(void *table, int pfd, uint32_t window_size);
+const ppc_def_t *kvmppc_host_cpu_def(void);
 
 #else
 
@@ -83,6 +84,11 @@ static inline int kvmppc_remove_spapr_tce(void *table, int 
pfd,
     return -1;
 }
 
+static inline const ppc_def_t *kvmppc_host_cpu_def(void)
+{
+    return NULL;
+}
+
 #endif
 
 #ifndef CONFIG_KVM
diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
index 73b49cf..62f0a6b 100644
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -24,6 +24,8 @@
 
 #include "dis-asm.h"
 #include "gdbstub.h"
+#include <kvm.h>
+#include "kvm_ppc.h"
 
 //#define PPC_DUMP_CPU
 //#define PPC_DEBUG_SPR
@@ -10041,7 +10043,7 @@ int cpu_ppc_register_internal (CPUPPCState *env, const 
ppc_def_t *def)
     return 0;
 }
 
-static const ppc_def_t *ppc_find_by_pvr (uint32_t pvr)
+const ppc_def_t *ppc_find_by_pvr(uint32_t pvr)
 {
     int i;
 
@@ -10063,6 +10065,10 @@ const ppc_def_t *cpu_ppc_find_by_name (const char 
*name)
     const char *p;
     int i, max, len;
 
+    if (kvm_enabled() && (strcasecmp(name, "host") == 0)) {
+        return kvmppc_host_cpu_def();
+    }
+
     /* Check if the given name is a PVR */
     len = strlen(name);
     if (len == 10 && name[0] == '0' && name[1] == 'x') {
-- 
1.7.6.3