[PATCH] target/mips: Fix PageMask with variable page size

[Jiaxun Yang]

Our current code assumed the target page size is always 4k
when handling PageMask and VPN2, however, variable page size
was just added to mips target and that's nolonger true.

So we refined this piece of code to handle any target page size.
Also added Big Page support defined by MIPS64 Release2.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 target/mips/cp0_helper.c | 48 ++++++++++++++++++++++++++++++----------
 target/mips/cpu.h        |  3 ++-
 2 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/target/mips/cp0_helper.c b/target/mips/cp0_helper.c
index bbf12e4a97..7a134085f7 100644
--- a/target/mips/cp0_helper.c
+++ b/target/mips/cp0_helper.c
@@ -872,20 +872,44 @@ void helper_mtc0_memorymapid(CPUMIPSState *env, 
target_ulong arg1)
     }
 }
 
-void update_pagemask(CPUMIPSState *env, target_ulong arg1, int32_t *pagemask)
+void helper_mtc0_pagemask(CPUMIPSState *env, target_ulong arg1)
 {
-    uint64_t mask = arg1 >> (TARGET_PAGE_BITS + 1);
-    if (!(env->insn_flags & ISA_MIPS32R6) || (arg1 == ~0) ||
-        (mask == 0x0000 || mask == 0x0003 || mask == 0x000F ||
-         mask == 0x003F || mask == 0x00FF || mask == 0x03FF ||
-         mask == 0x0FFF || mask == 0x3FFF || mask == 0xFFFF)) {
-        env->CP0_PageMask = arg1 & (0x1FFFFFFF & (TARGET_PAGE_MASK << 1));
+    uint64_t mask;
+    int maxmaskbits, maskbits;
+
+    if (env->insn_flags & ISA_MIPS32R6) {
+        return;
     }
-}
 
-void helper_mtc0_pagemask(CPUMIPSState *env, target_ulong arg1)
-{
-    update_pagemask(env, arg1, &env->CP0_PageMask);
+    /* Don't care MASKX as we don't support 1KB page */
+#ifdef TARGET_MIPS64
+    if (env->CP0_Config3 & CP0C3_BPG) {
+        maxmaskbits = 47;
+    } else {
+        maxmaskbits = 16;
+    }
+#else
+    maxmaskbits = 16;
+#endif
+    mask = extract64((uint64_t)arg1, CP0PM_MASK, maxmaskbits);
+
+    maskbits = find_first_zero_bit(&mask, 64);
+
+    /* Ensure no more set bit after first zero */
+    if (mask >> maskbits) {
+        goto invalid;
+    }
+    /* We don't support VTLB entry smaller than target page */
+    if ((maskbits + 12) < TARGET_PAGE_BITS) {
+        goto invalid;
+    }
+    env->CP0_PageMask = mask << CP0PM_MASK;
+
+    return;
+
+invalid:
+    maskbits = MIN(maxmaskbits, MAX(maskbits, TARGET_PAGE_BITS - 12));
+    env->CP0_PageMask = ((1 << (maskbits + 1)) - 1) << CP0PM_MASK;
 }
 
 void helper_mtc0_pagegrain(CPUMIPSState *env, target_ulong arg1)
@@ -1111,7 +1135,7 @@ void helper_mthc0_saar(CPUMIPSState *env, target_ulong 
arg1)
 void helper_mtc0_entryhi(CPUMIPSState *env, target_ulong arg1)
 {
     target_ulong old, val, mask;
-    mask = (TARGET_PAGE_MASK << 1) | env->CP0_EntryHi_ASID_mask;
+    mask = ~((1 << 14) - 1) | env->CP0_EntryHi_ASID_mask;
     if (((env->CP0_Config4 >> CP0C4_IE) & 0x3) >= 2) {
         mask |= 1 << CP0EnHi_EHINV;
     }
diff --git a/target/mips/cpu.h b/target/mips/cpu.h
index 0b3c987bb3..b69806792d 100644
--- a/target/mips/cpu.h
+++ b/target/mips/cpu.h
@@ -617,7 +617,8 @@ struct CPUMIPSState {
 /*
  * CP0 Register 5
  */
-    int32_t CP0_PageMask;
+    target_ulong CP0_PageMask;
+#define CP0PM_MASK 13
     int32_t CP0_PageGrain_rw_bitmask;
     int32_t CP0_PageGrain;
 #define CP0PG_RIE 31
-- 
2.27.0.rc2