[Qemu-devel] [PATCH 2/3] softmmu: support up to 12 MMU modes

[Paolo Bonzini <pbonzini@redhat.com>]

At 8k per TLB (for 64-bit host or target), 8 or more modes
make the TLBs bigger than 64k, and some RISC TCG backends do
not like that.  On the affected hosts, cut the TLB size in
half---there is still a measurable speedup on PPC with the
next patch.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 include/exec/cpu-defs.h |  34 +++++++++++++++-
 include/exec/cpu_ldst.h | 104 +++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 130 insertions(+), 8 deletions(-)

diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h
index 0ca6f0b..2662de5 100644
--- a/include/exec/cpu-defs.h
+++ b/include/exec/cpu-defs.h
@@ -27,6 +27,7 @@
 #include <inttypes.h>
 #include "qemu/osdep.h"
 #include "qemu/queue.h"
+#include "tcg-target.h"
 #ifndef CONFIG_USER_ONLY
 #include "exec/hwaddr.h"
 #endif
@@ -69,8 +70,6 @@ typedef uint64_t target_ulong;
 #define TB_JMP_PAGE_MASK (TB_JMP_CACHE_SIZE - TB_JMP_PAGE_SIZE)
 
 #if !defined(CONFIG_USER_ONLY)
-#define CPU_TLB_BITS 8
-#define CPU_TLB_SIZE (1 << CPU_TLB_BITS)
 /* use a fully associative victim tlb of 8 entries */
 #define CPU_VTLB_SIZE 8
 
@@ -80,6 +79,37 @@ typedef uint64_t target_ulong;
 #define CPU_TLB_ENTRY_BITS 5
 #endif
 
+/* TCG_TARGET_TLB_DISPLACEMENT_BITS is used in CPU_TLB_BITS to ensure that
+ * the TLB is not unnecessarily small, but still small enough for the
+ * TLB lookup instruction sequence used by the TCG target.
+ *
+ * TCG will have to generate an operand as large as the distance between
+ * tlb_table[0][0] and the tlb_table[NB_MMU_MODES - 1][0].addend.  For
+ * simplicity, the TCG targets just round everything up to the next
+ * power of two, and count bits.  This works because: 1) the size of each
+ * TLB is a largish power of two, 2) and because the limit of the
+ * displacement is really close to a power of two.
+ *
+ * For example, the maximum displacement 0xFFF0 on PPC and MIPS, but TCG
+ * just says "the displacement is 16 bits".  TCG_TARGET_TLB_DISPLACEMENT_BITS
+ * then ensures that tlb_table at least 0x8000 bytes large ("not unnecessarily
+ * small": 2^15).  The operand then will come up smaller than 0xFFF0 without
+ * any particular care, because the TLB for a single MMU mode is larger than
+ * 0x10000-0xFFF0=16 bytes.  In the end, the maximum value of the operand
+ * will be something like 0xC018; here, 0xC000 is the offset of the last TLB
+ * table (tlb_table[NB_MMU_MODES - 1][0]), and 0x18 is the offset of the
+ * addend field in each TLB entry.
+ */
+#define CPU_TLB_BITS                                             \
+    MIN(8,                                                       \
+        TCG_TARGET_TLB_DISPLACEMENT_BITS - CPU_TLB_ENTRY_BITS -  \
+        (NB_MMU_MODES <= 1 ? 0 :                                 \
+         NB_MMU_MODES <= 2 ? 1 :                                 \
+         NB_MMU_MODES <= 4 ? 2 :                                 \
+         NB_MMU_MODES <= 8 ? 3 : 4))
+
+#define CPU_TLB_SIZE (1 << CPU_TLB_BITS)
+
 typedef struct CPUTLBEntry {
     /* bit TARGET_LONG_BITS to TARGET_PAGE_BITS : virtual address
        bit TARGET_PAGE_BITS-1..4  : Nonzero for accesses that should not
diff --git a/include/exec/cpu_ldst.h b/include/exec/cpu_ldst.h
index 1673287..0ec398c 100644
--- a/include/exec/cpu_ldst.h
+++ b/include/exec/cpu_ldst.h
@@ -263,12 +263,104 @@ uint64_t helper_ldq_cmmu(CPUArchState *env, target_ulong addr, int mmu_idx);
 #undef MEMSUFFIX
 #endif /* (NB_MMU_MODES >= 7) */
 
-#if (NB_MMU_MODES > 7)
-/* Note that supporting NB_MMU_MODES == 9 would require
- * changes to at least the ARM TCG backend.
- */
-#error "NB_MMU_MODES > 7 is not supported for now"
-#endif /* (NB_MMU_MODES > 7) */
+#if (NB_MMU_MODES >= 8) && defined(MMU_MODE7_SUFFIX)
+
+#define CPU_MMU_INDEX 7
+#define MEMSUFFIX MMU_MODE7_SUFFIX
+#define DATA_SIZE 1
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 2
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 4
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 8
+#include "exec/cpu_ldst_template.h"
+#undef CPU_MMU_INDEX
+#undef MEMSUFFIX
+#endif /* (NB_MMU_MODES >= 8) */
+
+#if (NB_MMU_MODES >= 9) && defined(MMU_MODE8_SUFFIX)
+
+#define CPU_MMU_INDEX 8
+#define MEMSUFFIX MMU_MODE8_SUFFIX
+#define DATA_SIZE 1
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 2
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 4
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 8
+#include "exec/cpu_ldst_template.h"
+#undef CPU_MMU_INDEX
+#undef MEMSUFFIX
+#endif /* (NB_MMU_MODES >= 9) */
+
+#if (NB_MMU_MODES >= 10) && defined(MMU_MODE9_SUFFIX)
+
+#define CPU_MMU_INDEX 9
+#define MEMSUFFIX MMU_MODE9_SUFFIX
+#define DATA_SIZE 1
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 2
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 4
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 8
+#include "exec/cpu_ldst_template.h"
+#undef CPU_MMU_INDEX
+#undef MEMSUFFIX
+#endif /* (NB_MMU_MODES >= 10) */
+
+#if (NB_MMU_MODES >= 11) && defined(MMU_MODE10_SUFFIX)
+
+#define CPU_MMU_INDEX 10
+#define MEMSUFFIX MMU_MODE10_SUFFIX
+#define DATA_SIZE 1
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 2
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 4
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 8
+#include "exec/cpu_ldst_template.h"
+#undef CPU_MMU_INDEX
+#undef MEMSUFFIX
+#endif /* (NB_MMU_MODES >= 11) */
+
+#if (NB_MMU_MODES >= 12) && defined(MMU_MODE11_SUFFIX)
+
+#define CPU_MMU_INDEX 11
+#define MEMSUFFIX MMU_MODE11_SUFFIX
+#define DATA_SIZE 1
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 2
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 4
+#include "exec/cpu_ldst_template.h"
+
+#define DATA_SIZE 8
+#include "exec/cpu_ldst_template.h"
+#undef CPU_MMU_INDEX
+#undef MEMSUFFIX
+#endif /* (NB_MMU_MODES >= 12) */
+
+#if (NB_MMU_MODES > 12)
+#error "NB_MMU_MODES > 12 is not supported for now"
+#endif /* (NB_MMU_MODES > 12) */
 
 /* these access are slower, they must be as rare as possible */
 #define CPU_MMU_INDEX (cpu_mmu_index(env))
-- 
2.3.0