[Qemu-devel] [PATCH 2/2] pseries: Add device tree properties for VMX/VSX and DFP under kvm

[David Gibson <david@gibson.dropbear.id.au>]

Sufficiently recent PAPR specifications define properties "ibm,vmx"
and "ibm,dfp" on the CPU node which advertise whether the VMX vector
extensions (or the later VSX version) and/or the Decimal Floating
Point operations from IBM's recent POWER CPUs are available.

Currently we do not put these in the guest device tree and the guest
kernel will consequently assume they are not available.  This is good,
because they are not supported under TCG.  VMX is similar enough to
Altivec that it might be trivial to support, but VSX and DFP would
both require significant work to support in TCG.

However, when running under kvm on a host which supports these
instructions, there's no reason not to let the guest use them.  This
patch, therefore, checks for the relevant support on the host CPU
and, if present, advertises them to the guest as well.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/spapr.c           |   17 +++++++++++++++++
 target-ppc/kvm.c     |   10 ++++++++++
 target-ppc/kvm_ppc.h |   12 ++++++++++++
 3 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/hw/spapr.c b/hw/spapr.c
index 9a3a1ea..00b9c67 100644
--- a/hw/spapr.c
+++ b/hw/spapr.c
@@ -186,6 +186,8 @@ static void *spapr_create_fdt_skel(const char *cpu_model,
                            0xffffffff, 0xffffffff};
         uint32_t tbfreq = kvm_enabled() ? kvmppc_get_tbfreq() : TIMEBASE_FREQ;
         uint32_t cpufreq = kvm_enabled() ? kvmppc_get_clockfreq() : 1000000000;
+        uint32_t vmx = kvm_enabled() ? kvmppc_get_vmx() : 0;
+        uint32_t dfp = kvm_enabled() ? kvmppc_get_dfp() : 0;
 
         if ((index % smt) != 0) {
             continue;
@@ -233,6 +235,21 @@ static void *spapr_create_fdt_skel(const char *cpu_model,
                                segs, sizeof(segs))));
         }
 
+        /* Advertise VMX/VSX (vector extensions) if available
+         *   0 / no property == no vector extensions
+         *   1               == VMX / Altivec available
+         *   2               == VSX available */
+        if (vmx) {
+            _FDT((fdt_property_cell(fdt, "ibm,vmx", vmx)));
+        }
+
+        /* Advertise DFP (Decimal Floating Point) if available
+         *   0 / no property == no DFP
+         *   1               == DFP available */
+        if (dfp) {
+            _FDT((fdt_property_cell(fdt, "ibm,dfp", dfp)));
+        }
+
         _FDT((fdt_end_node(fdt)));
     }
 
diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index 6667b61..6a48eb4 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -694,6 +694,16 @@ uint64_t kvmppc_get_clockfreq(void)
     return kvmppc_read_int_cpu_dt("clock-frequency");
 }
 
+uint32_t kvmppc_get_vmx(void)
+{
+    return kvmppc_read_int_cpu_dt("ibm,vmx");
+}
+
+uint32_t kvmppc_get_dfp(void)
+{
+    return kvmppc_read_int_cpu_dt("ibm,dfp");
+}
+
 int kvmppc_get_hypercall(CPUState *env, uint8_t *buf, int buf_len)
 {
     uint32_t *hc = (uint32_t*)buf;
diff --git a/target-ppc/kvm_ppc.h b/target-ppc/kvm_ppc.h
index 9e8a7b5..fa131bf 100644
--- a/target-ppc/kvm_ppc.h
+++ b/target-ppc/kvm_ppc.h
@@ -15,6 +15,8 @@ void kvmppc_init(void);
 
 uint32_t kvmppc_get_tbfreq(void);
 uint64_t kvmppc_get_clockfreq(void);
+uint32_t kvmppc_get_vmx(void);
+uint32_t kvmppc_get_dfp(void);
 int kvmppc_get_hypercall(CPUState *env, uint8_t *buf, int buf_len);
 int kvmppc_set_interrupt(CPUState *env, int irq, int level);
 void kvmppc_set_papr(CPUState *env);
@@ -35,6 +37,16 @@ static inline uint64_t kvmppc_get_clockfreq(void)
     return 0;
 }
 
+static inline uint32_t kvmppc_get_vmx(void)
+{
+    return 0;
+}
+
+static inline uint32_t kvmppc_get_dfp(void)
+{
+    return 0;
+}
+
 static inline int kvmppc_get_hypercall(CPUState *env, uint8_t *buf, int buf_len)
 {
     return -1;
-- 
1.7.6.3