target-ppc: Eliminate kvmppc_kern_htab global

fa48b43 "target-ppc: Remove hack for ppc_hash64_load_hpte*() with HV KVM"
purports to remove a hack in the handling of hash page tables (HPTs)
managed by KVM instead of qemu.  However, it actually went in the wrong
direction.

That patch requires anything looking for an external HPT (that is one not
managed by the guest itself) to check both env->external_htab (for a qemu
managed HPT) and kvmppc_kern_htab (for a KVM managed HPT).  That's a
problem because kvmppc_kern_htab is local to mmu-hash64.c, but some places
which need to check for an external HPT are outside that, such as
kvm_arch_get_registers().  The latter was subtly broken by the earlier
patch such that gdbstub can no longer access memory.

Basically a KVM managed HPT is much more like a qemu managed HPT than it is
like a guest managed HPT, so the original "hack" was actually on the right
track.

This partially reverts fa48b43, so we again mark a KVM managed external HPT
by putting a special but non-NULL value in env->external_htab.  It then
goes further, using that marker to eliminate the kvmppc_kern_htab global
entirely.  The ppc_hash64_set_external_hpt() helper function is extended
to set that marker if passed a NULL value (if you're setting an external
HPT, but don't have an actual HPT to set, the assumption is that it must
be a KVM managed HPT).

This also has some flow-on changes to the HPT access helpers, required by
the above changes.

Reported-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Tested-by: Greg Kurz <gkurz@linux.vnet.ibm.com>

2 files changed, 21 insertions, 28 deletions

diff --git a/target-ppc/mmu-hash64.c b/target-ppc/mmu-hash64.c
index 7b5200bdc6..d175fdad45 100644
--- a/target-ppc/mmu-hash64.c
+++ b/target-ppc/mmu-hash64.c
@@ -36,10 +36,11 @@
 #endif
 
 /*
- * Used to indicate whether we have allocated htab in the
- * host kernel
+ * Used to indicate that a CPU has its hash page table (HPT) managed
+ * within the host kernel
  */
-bool kvmppc_kern_htab;
+#define MMU_HASH64_KVM_MANAGED_HPT      ((void *)-1)
+
 /*
  * SLB handling
  */
@@ -283,7 +284,11 @@ void ppc_hash64_set_external_hpt(PowerPCCPU *cpu, void *hpt, int shift,
 
     cpu_synchronize_state(CPU(cpu));
 
-    env->external_htab = hpt;
+    if (hpt) {
+        env->external_htab = hpt;
+    } else {
+        env->external_htab = MMU_HASH64_KVM_MANAGED_HPT;
+    }
     ppc_hash64_set_sdr1(cpu, (target_ulong)(uintptr_t)hpt | (shift - 18),
                         &local_err);
     if (local_err) {
@@ -396,25 +401,16 @@ uint64_t ppc_hash64_start_access(PowerPCCPU *cpu, target_ulong pte_index)
     hwaddr pte_offset;
 
     pte_offset = pte_index * HASH_PTE_SIZE_64;
-    if (kvmppc_kern_htab) {
+    if (cpu->env.external_htab == MMU_HASH64_KVM_MANAGED_HPT) {
         /*
          * HTAB is controlled by KVM. Fetch the PTEG into a new buffer.
          */
         token = kvmppc_hash64_read_pteg(cpu, pte_index);
-        if (token) {
-            return token;
-        }
+    } else if (cpu->env.external_htab) {
         /*
-         * pteg read failed, even though we have allocated htab via
-         * kvmppc_reset_htab.
+         * HTAB is controlled by QEMU. Just point to the internally
+         * accessible PTEG.
          */
-        return 0;
-    }
-    /*
-     * HTAB is controlled by QEMU. Just point to the internally
-     * accessible PTEG.
-     */
-    if (cpu->env.external_htab) {
         token = (uint64_t)(uintptr_t) cpu->env.external_htab + pte_offset;
     } else if (cpu->env.htab_base) {
         token = cpu->env.htab_base + pte_offset;
@@ -422,9 +418,9 @@ uint64_t ppc_hash64_start_access(PowerPCCPU *cpu, target_ulong pte_index)
     return token;
 }
 
-void ppc_hash64_stop_access(uint64_t token)
+void ppc_hash64_stop_access(PowerPCCPU *cpu, uint64_t token)
 {
-    if (kvmppc_kern_htab) {
+    if (cpu->env.external_htab == MMU_HASH64_KVM_MANAGED_HPT) {
         kvmppc_hash64_free_pteg(token);
     }
 }
@@ -453,11 +449,11 @@ static hwaddr ppc_hash64_pteg_search(PowerPCCPU *cpu, hwaddr hash,
             && HPTE64_V_COMPARE(pte0, ptem)) {
             pte->pte0 = pte0;
             pte->pte1 = pte1;
-            ppc_hash64_stop_access(token);
+            ppc_hash64_stop_access(cpu, token);
             return (pte_index + i) * HASH_PTE_SIZE_64;
         }
     }
-    ppc_hash64_stop_access(token);
+    ppc_hash64_stop_access(cpu, token);
     /*
      * We didn't find a valid entry.
      */
@@ -772,7 +768,7 @@ void ppc_hash64_store_hpte(PowerPCCPU *cpu,
 {
     CPUPPCState *env = &cpu->env;
 
-    if (kvmppc_kern_htab) {
+    if (env->external_htab == MMU_HASH64_KVM_MANAGED_HPT) {
         kvmppc_hash64_write_pte(env, pte_index, pte0, pte1);
         return;
     }
diff --git a/target-ppc/mmu-hash64.h b/target-ppc/mmu-hash64.h
index 138cd7e3ad..9bf8b9b267 100644
--- a/target-ppc/mmu-hash64.h
+++ b/target-ppc/mmu-hash64.h
@@ -90,16 +90,13 @@ unsigned ppc_hash64_hpte_page_shift_noslb(PowerPCCPU *cpu,
 #define HPTE64_V_1TB_SEG        0x4000000000000000ULL
 #define HPTE64_V_VRMA_MASK      0x4001ffffff000000ULL
 
-
-extern bool kvmppc_kern_htab;
-
 void ppc_hash64_set_sdr1(PowerPCCPU *cpu, target_ulong value,
                          Error **errp);
 void ppc_hash64_set_external_hpt(PowerPCCPU *cpu, void *hpt, int shift,
                                  Error **errp);
 
 uint64_t ppc_hash64_start_access(PowerPCCPU *cpu, target_ulong pte_index);
-void ppc_hash64_stop_access(uint64_t token);
+void ppc_hash64_stop_access(PowerPCCPU *cpu, uint64_t token);
 
 static inline target_ulong ppc_hash64_load_hpte0(PowerPCCPU *cpu,
                                                  uint64_t token, int index)
@@ -108,7 +105,7 @@ static inline target_ulong ppc_hash64_load_hpte0(PowerPCCPU *cpu,
     uint64_t addr;
 
     addr = token + (index * HASH_PTE_SIZE_64);
-    if (kvmppc_kern_htab || env->external_htab) {
+    if (env->external_htab) {
         return  ldq_p((const void *)(uintptr_t)addr);
     } else {
         return ldq_phys(CPU(cpu)->as, addr);
@@ -122,7 +119,7 @@ static inline target_ulong ppc_hash64_load_hpte1(PowerPCCPU *cpu,
     uint64_t addr;
 
     addr = token + (index * HASH_PTE_SIZE_64) + HASH_PTE_SIZE_64/2;
-    if (kvmppc_kern_htab || env->external_htab) {
+    if (env->external_htab) {
         return  ldq_p((const void *)(uintptr_t)addr);
     } else {
         return ldq_phys(CPU(cpu)->as, addr);