[Qemu-devel] [RFC 10/17] pseries: Rewrite CAS PVR compatibility logic

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

During boot, PAPR guests negotiate CPU model support with the
ibm,client-architecture-support mechanism.  The logic to implement this in
qemu is very convoluted.  This cleans it up to be cleaner, using the new
ppc_check_compat() call.

The new logic for choosing a compatibility mode is:
    1. If the guest lists the CPU's real PVR as supported *AND* no
       maximum compatibility mode has been requested on the command line
       then we use "raw" mode - the CPU acts with full capabilities.
    2. Otherwise, we pick the most recent compatibility mode which is
       both supported by the CPU, and is advertised as supported by the
       guest.
I think the original code approximated the same thing, but it's hard to be
sure, and I think it had some weird edge cases.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/ppc/spapr_hcall.c | 107 +++++++++++++++++----------------------------------
 hw/ppc/trace-events  |   2 +-
 2 files changed, 37 insertions(+), 72 deletions(-)

diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index d93f580..3bd6d06 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -895,98 +895,63 @@ static void do_set_compat(CPUState *cs, void *arg)
     ppc_set_compat(cpu, s->compat_pvr, &s->err);
 }
 
-#define get_compat_level(cpuver) ( \
-    ((cpuver) == CPU_POWERPC_LOGICAL_2_05) ? 2050 : \
-    ((cpuver) == CPU_POWERPC_LOGICAL_2_06) ? 2060 : \
-    ((cpuver) == CPU_POWERPC_LOGICAL_2_06_PLUS) ? 2061 : \
-    ((cpuver) == CPU_POWERPC_LOGICAL_2_07) ? 2070 : 0)
-
-static void cas_handle_compat_cpu(PowerPCCPUClass *pcc, uint32_t pvr,
-                                  unsigned max_lvl, unsigned *compat_lvl,
-                                  unsigned *compat_pvr)
-{
-    unsigned lvl = get_compat_level(pvr);
-    bool is205, is206, is207;
-
-    if (!lvl) {
-        return;
-    }
-
-    /* If it is a logical PVR, try to determine the highest level */
-    is205 = (pcc->pcr_supported & PCR_COMPAT_2_05) &&
-            (lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_05));
-    is206 = (pcc->pcr_supported & PCR_COMPAT_2_06) &&
-            ((lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_06)) ||
-             (lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_06_PLUS)));
-    is207 = (pcc->pcr_supported & PCR_COMPAT_2_07) &&
-            (lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_07));
-
-    if (is205 || is206 || is207) {
-        if (!max_lvl) {
-            /* User did not set the level, choose the highest */
-            if (*compat_lvl <= lvl) {
-                *compat_lvl = lvl;
-                *compat_pvr = pvr;
-            }
-        } else if (max_lvl >= lvl) {
-            /* User chose the level, don't set higher than this */
-            *compat_lvl = lvl;
-            *compat_pvr = pvr;
-        }
-    }
-}
-
-static target_ulong h_client_architecture_support(PowerPCCPU *cpu_,
+static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
                                                   sPAPRMachineState *spapr,
                                                   target_ulong opcode,
                                                   target_ulong *args)
 {
     target_ulong list = ppc64_phys_to_real(args[0]);
     target_ulong ov_table;
-    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu_);
     CPUState *cs;
-    bool cpu_match = false;
-    unsigned old_compat_pvr = cpu_->compat_pvr;
-    unsigned compat_lvl = 0, compat_pvr = 0;
-    unsigned max_lvl = get_compat_level(cpu_->max_compat);
-    int counter;
+    bool explicit_match = false; /* Matched the CPU's real PVR */
+    uint32_t max_compat = cpu->max_compat;
+    uint32_t best_compat = 0;
+    int i;
     sPAPROptionVector *ov5_guest, *ov5_cas_old, *ov5_updates;
 
-    /* Parse PVR list */
-    for (counter = 0; counter < 512; ++counter) {
+    /*
+     * We scan the supplied table of PVRs looking for two things
+     *   1. Is our real CPU PVR in the list?
+     *   2. What's the "best" listed logical PVR
+     */
+    for (i = 0; i < 512; ++i) {
         uint32_t pvr, pvr_mask;
 
-        pvr_mask = ldl_be_phys(&address_space_memory, list);
-        list += 4;
         pvr = ldl_be_phys(&address_space_memory, list);
-        list += 4;
-
-        trace_spapr_cas_pvr_try(pvr);
-        if (!max_lvl &&
-            ((cpu_->env.spr[SPR_PVR] & pvr_mask) == (pvr & pvr_mask))) {
-            cpu_match = true;
-            compat_pvr = 0;
-        } else if (pvr == cpu_->compat_pvr) {
-            cpu_match = true;
-            compat_pvr = cpu_->compat_pvr;
-        } else if (!cpu_match) {
-            cas_handle_compat_cpu(pcc, pvr, max_lvl, &compat_lvl, &compat_pvr);
-        }
-        /* Terminator record */
+        pvr_mask = ldl_be_phys(&address_space_memory, list + 4);
+        list += 8;
+
         if (~pvr_mask & pvr) {
-            break;
+            break; /* Terminator record */
         }
+
+        if ((cpu->env.spr[SPR_PVR] & pvr_mask) == (pvr & pvr_mask)) {
+            explicit_match = true;
+        } else {
+            if (ppc_check_compat(cpu, pvr, best_compat, max_compat)) {
+                best_compat = pvr;
+            }
+        }
+    }
+
+    if (!max_compat && explicit_match) {
+        /* If the guest explicitly supports the CPU, *and* user hasn't
+         * requested a compatibility mode, use "raw" mode */
+        best_compat = 0;
+    } else if (best_compat == 0) {
+        /* Didn't find any supported compat modes */
+        /* FIXME: what's the right error here? */
+        return H_HARDWARE;
     }
 
     /* Parsing finished */
-    trace_spapr_cas_pvr(cpu_->compat_pvr, cpu_match,
-                        compat_pvr, pcc->pcr_mask);
+    trace_spapr_cas_pvr(cpu->compat_pvr, explicit_match, best_compat);
 
     /* Update CPUs */
-    if (old_compat_pvr != compat_pvr) {
+    if (cpu->compat_pvr != best_compat) {
         CPU_FOREACH(cs) {
             SetCompatState s = {
-                .compat_pvr = compat_pvr,
+                .compat_pvr = best_compat,
                 .err = NULL,
             };
 
diff --git a/hw/ppc/trace-events b/hw/ppc/trace-events
index 2297ead..604ac92 100644
--- a/hw/ppc/trace-events
+++ b/hw/ppc/trace-events
@@ -15,7 +15,7 @@ spapr_cas_continue(unsigned long n) "Copy changes to the guest: %ld bytes"
 
 # hw/ppc/spapr_hcall.c
 spapr_cas_pvr_try(uint32_t pvr) "%x"
-spapr_cas_pvr(uint32_t cur_pvr, bool cpu_match, uint32_t new_pvr, uint64_t pcr) "current=%x, cpu_match=%u, new=%x, compat flags=%"PRIx64
+spapr_cas_pvr(uint32_t cur_pvr, bool explicit_match, uint32_t new_pvr) "current=%x, explicit_match=%u, new=%x"
 
 # hw/ppc/spapr_iommu.c
 spapr_iommu_put(uint64_t liobn, uint64_t ioba, uint64_t tce, uint64_t ret) "liobn=%"PRIx64" ioba=0x%"PRIx64" tce=0x%"PRIx64" ret=%"PRId64
-- 
2.7.4