page-vary: Restrict scope of TARGET_PAGE_BITS_MIN

The only place we really need to know the minimum is within
page-vary-target.c.  Rename the target/arm TARGET_PAGE_BITS_MIN
to TARGET_PAGE_BITS_LEGACY to emphasize what it really means.
Move the assertions related to minimum page size as well.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/cputlb.c

@@ -49,7 +49,6 @@
 #endif
 #include "tcg/tcg-ldst.h"
 
-QEMU_BUILD_BUG_ON(TLB_FLAGS_MASK & ((1u < TARGET_PAGE_BITS_MIN) - 1));
 
 /* DEBUG defines, enable DEBUG_TLB_LOG to log to the CPU_LOG_MMU target */
 /* #define DEBUG_TLB */

include/exec/cpu-defs.h

@@ -34,14 +34,8 @@
 #ifndef TARGET_VIRT_ADDR_SPACE_BITS
 # error TARGET_VIRT_ADDR_SPACE_BITS must be defined in cpu-param.h
 #endif
-#ifndef TARGET_PAGE_BITS
-# ifdef TARGET_PAGE_BITS_VARY
-#  ifndef TARGET_PAGE_BITS_MIN
-#   error TARGET_PAGE_BITS_MIN must be defined in cpu-param.h
-#  endif
-# else
-#  error TARGET_PAGE_BITS must be defined in cpu-param.h
-# endif
+#if !defined(TARGET_PAGE_BITS) && !defined(TARGET_PAGE_BITS_VARY)
+# error TARGET_PAGE_BITS must be defined in cpu-param.h
 #endif
 
 #include "exec/target_long.h"

include/exec/target_page.h

@@ -41,7 +41,6 @@ extern const TargetPageBits target_page;
 # endif
 # define TARGET_PAGE_SIZE    (-(int)TARGET_PAGE_MASK)
 #else
-# define TARGET_PAGE_BITS_MIN TARGET_PAGE_BITS
 # define TARGET_PAGE_SIZE    (1 << TARGET_PAGE_BITS)
 # define TARGET_PAGE_MASK    ((TARGET_PAGE_TYPE)-1 << TARGET_PAGE_BITS)
 #endif

page-vary-target.c

@@ -23,19 +23,45 @@
 #include "exec/page-vary.h"
 #include "exec/target_page.h"
 
+
+/*
+ * For system mode, the minimum comes from the number of bits
+ * required for maximum alignment (6) and the number of bits
+ * required for TLB_FLAGS_MASK (3).
+ *
+ * For user mode, TARGET_PAGE_BITS_VARY is a hack to allow the target
+ * page size to match the host page size.  Mostly, this reduces the
+ * ordinary target page size to run on a host with 4KiB pages (i.e. x86).
+ * There is no true minimum required by the implementation, but keep the
+ * same minimum as for system mode for sanity.
+ * See linux-user/mmap.c, mmap_h_lt_g and mmap_h_gt_g.
+ */
+#define TARGET_PAGE_BITS_MIN 9
+
+#ifndef TARGET_PAGE_BITS_VARY
+QEMU_BUILD_BUG_ON(TARGET_PAGE_BITS < TARGET_PAGE_BITS_MIN);
+#endif
+
+#ifndef CONFIG_USER_ONLY
+#include "exec/tlb-flags.h"
+
+QEMU_BUILD_BUG_ON(TLB_FLAGS_MASK & ((1u < TARGET_PAGE_BITS_MIN) - 1));
+
 int migration_legacy_page_bits(void)
 {
 #ifdef TARGET_PAGE_BITS_VARY
-    return TARGET_PAGE_BITS_MIN;
+    QEMU_BUILD_BUG_ON(TARGET_PAGE_BITS_LEGACY < TARGET_PAGE_BITS_MIN);
+    return TARGET_PAGE_BITS_LEGACY;
 #else
     return TARGET_PAGE_BITS;
 #endif
 }
+#endif
 
 bool set_preferred_target_page_bits(int bits)
 {
-#ifdef TARGET_PAGE_BITS_VARY
     assert(bits >= TARGET_PAGE_BITS_MIN);
+#ifdef TARGET_PAGE_BITS_VARY
     return set_preferred_target_page_bits_common(bits);
 #else
     return true;
@@ -44,5 +70,12 @@ bool set_preferred_target_page_bits(int bits)
 
 void finalize_target_page_bits(void)
 {
-    finalize_target_page_bits_common(TARGET_PAGE_BITS_MIN);
+#ifndef TARGET_PAGE_BITS_VARY
+    finalize_target_page_bits_common(TARGET_PAGE_BITS);
+#elif defined(CONFIG_USER_ONLY)
+    assert(target_page.bits != 0);
+    finalize_target_page_bits_common(target_page.bits);
+#else
+    finalize_target_page_bits_common(TARGET_PAGE_BITS_LEGACY);
+#endif
 }

target/alpha/cpu-param.h

@@ -18,7 +18,6 @@
  * a 4k minimum to match x86 host, which can minimize emulation issues.
  */
 # define TARGET_PAGE_BITS_VARY
-# define TARGET_PAGE_BITS_MIN 12
 # define TARGET_VIRT_ADDR_SPACE_BITS  63
 #else
 # define TARGET_PAGE_BITS 13

target/arm/cpu-param.h

@@ -24,7 +24,6 @@
 # else
 /* Allow user-only to vary page size from 4k */
 #  define TARGET_PAGE_BITS_VARY
-#  define TARGET_PAGE_BITS_MIN  12
 # endif
 # else
 #  define TARGET_PAGE_BITS 12
@@ -35,7 +34,7 @@
  * have to support 1K tiny pages.
  */
 # define TARGET_PAGE_BITS_VARY
-# define TARGET_PAGE_BITS_MIN  10
+# define TARGET_PAGE_BITS_LEGACY 10
 #endif /* !CONFIG_USER_ONLY */
 
 /* ARM processors have a weak memory model */

target/ppc/cpu-param.h

@@ -33,7 +33,6 @@
 #ifdef CONFIG_USER_ONLY
 /* Allow user-only to vary page size from 4k */
 # define TARGET_PAGE_BITS_VARY
-# define TARGET_PAGE_BITS_MIN 12
 #else
 # define TARGET_PAGE_BITS 12
 #endif