diff --git a/linux-user/aarch64/target_mman.h b/linux-user/aarch64/target_mman.h
index f721295fe1..4d3eecfb26 100644
--- a/linux-user/aarch64/target_mman.h
+++ b/linux-user/aarch64/target_mman.h
@@ -4,6 +4,16 @@
 #define TARGET_PROT_BTI         0x10
 #define TARGET_PROT_MTE         0x20
 
+/*
+ * arch/arm64/include/asm/processor.h:
+ *
+ * TASK_UNMAPPED_BASE     DEFAULT_MAP_WINDOW / 4
+ * DEFAULT_MAP_WINDOW     DEFAULT_MAP_WINDOW_64
+ * DEFAULT_MAP_WINDOW_64  UL(1) << VA_BITS_MIN
+ * VA_BITS_MIN            48 (unless explicitly configured smaller)
+ */
+#define TASK_UNMAPPED_BASE      (1ull << (48 - 2))
+
 #include "../generic/target_mman.h"
 
 #endif
diff --git a/linux-user/alpha/target_mman.h b/linux-user/alpha/target_mman.h
index 6bb03e7336..c90b493711 100644
--- a/linux-user/alpha/target_mman.h
+++ b/linux-user/alpha/target_mman.h
@@ -20,6 +20,14 @@
 #define TARGET_MS_SYNC 2
 #define TARGET_MS_INVALIDATE 4
 
+/*
+ * arch/alpha/include/asm/processor.h:
+ *
+ * TASK_UNMAPPED_BASE           TASK_SIZE / 2
+ * TASK_SIZE                    0x40000000000UL
+ */
+#define TASK_UNMAPPED_BASE      0x20000000000ull
+
 #include "../generic/target_mman.h"
 
 #endif
diff --git a/linux-user/arm/target_mman.h b/linux-user/arm/target_mman.h
index e7ba6070fe..76275b2c7e 100644
--- a/linux-user/arm/target_mman.h
+++ b/linux-user/arm/target_mman.h
@@ -1 +1,9 @@
+/*
+ * arch/arm/include/asm/memory.h
+ * TASK_UNMAPPED_BASE        ALIGN(TASK_SIZE / 3, SZ_16M)
+ * TASK_SIZE                 CONFIG_PAGE_OFFSET
+ * CONFIG_PAGE_OFFSET        0xC0000000 (default in Kconfig)
+ */
+#define TASK_UNMAPPED_BASE   0x40000000
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/cris/target_mman.h b/linux-user/cris/target_mman.h
index e7ba6070fe..9df7b1eda5 100644
--- a/linux-user/cris/target_mman.h
+++ b/linux-user/cris/target_mman.h
@@ -1 +1,10 @@
+/*
+ * arch/cris/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE      (PAGE_ALIGN(TASK_SIZE / 3))
+ *
+ * arch/cris/include/arch-v32/arch/processor.h
+ * TASK_SIZE               0xb0000000
+ */
+#define TASK_UNMAPPED_BASE TARGET_PAGE_ALIGN(0xb0000000 / 3)
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/hexagon/target_mman.h b/linux-user/hexagon/target_mman.h
index e7ba6070fe..c5ae336e07 100644
--- a/linux-user/hexagon/target_mman.h
+++ b/linux-user/hexagon/target_mman.h
@@ -1 +1,11 @@
+/*
+ * arch/hexgon/include/asm/processor.h
+ * TASK_UNMAPPED_BASE        PAGE_ALIGN(TASK_SIZE / 3)
+ *
+ * arch/hexagon/include/asm/mem-layout.h
+ * TASK_SIZE                 PAGE_OFFSET
+ * PAGE_OFFSET               0xc0000000
+ */
+#define TASK_UNMAPPED_BASE   0x40000000
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/hppa/target_mman.h b/linux-user/hppa/target_mman.h
index 97f87d042a..6459e7dbdd 100644
--- a/linux-user/hppa/target_mman.h
+++ b/linux-user/hppa/target_mman.h
@@ -24,6 +24,9 @@
 #define TARGET_MS_ASYNC 2
 #define TARGET_MS_INVALIDATE 4
 
+/* arch/parisc/include/asm/processor.h: DEFAULT_MAP_BASE32 */
+#define TASK_UNMAPPED_BASE      0x40000000
+
 #include "../generic/target_mman.h"
 
 #endif
diff --git a/linux-user/i386/target_mman.h b/linux-user/i386/target_mman.h
index e7ba6070fe..cc3382007f 100644
--- a/linux-user/i386/target_mman.h
+++ b/linux-user/i386/target_mman.h
@@ -1 +1,14 @@
+/*
+ * arch/x86/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE         __TASK_UNMAPPED_BASE(TASK_SIZE_LOW)
+ * __TASK_UNMAPPED_BASE(S)    PAGE_ALIGN(S / 3)
+ *
+ * arch/x86/include/asm/page_32_types.h:
+ * TASK_SIZE_LOW              TASK_SIZE
+ * TASK_SIZE                  __PAGE_OFFSET
+ * __PAGE_OFFSET              CONFIG_PAGE_OFFSET
+ * CONFIG_PAGE_OFFSET         0xc0000000 (default in Kconfig)
+ */
+#define TASK_UNMAPPED_BASE    0x40000000
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/loongarch64/target_mman.h b/linux-user/loongarch64/target_mman.h
index e7ba6070fe..d70e44d44c 100644
--- a/linux-user/loongarch64/target_mman.h
+++ b/linux-user/loongarch64/target_mman.h
@@ -1 +1,9 @@
+/*
+ * arch/loongarch/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE         PAGE_ALIGN(TASK_SIZE / 3)
+ * TASK_SIZE64                0x1UL << (... ? VA_BITS : ...)
+ */
+#define TASK_UNMAPPED_BASE \
+    TARGET_PAGE_ALIGN((1ull << TARGET_VIRT_ADDR_SPACE_BITS) / 3)
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/m68k/target_mman.h b/linux-user/m68k/target_mman.h
index e7ba6070fe..d3eceb663b 100644
--- a/linux-user/m68k/target_mman.h
+++ b/linux-user/m68k/target_mman.h
@@ -1 +1,4 @@
+/* arch/m68k/include/asm/processor.h */
+#define TASK_UNMAPPED_BASE      0xC0000000
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/microblaze/target_mman.h b/linux-user/microblaze/target_mman.h
index e7ba6070fe..ffee869db4 100644
--- a/linux-user/microblaze/target_mman.h
+++ b/linux-user/microblaze/target_mman.h
@@ -1 +1,9 @@
+/*
+ * arch/microblaze/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE           (TASK_SIZE / 8 * 3)
+ * TASK_SIZE                    CONFIG_KERNEL_START
+ * CONFIG_KERNEL_START          0xc0000000 (default in Kconfig)
+ */
+#define TASK_UNMAPPED_BASE      0x48000000
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/mips/target_mman.h b/linux-user/mips/target_mman.h
index e97694aa4e..fe1eec2d0b 100644
--- a/linux-user/mips/target_mman.h
+++ b/linux-user/mips/target_mman.h
@@ -14,6 +14,13 @@
 #define TARGET_MAP_STACK                0x40000
 #define TARGET_MAP_HUGETLB              0x80000
 
+/*
+ * arch/mips/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE         PAGE_ALIGN(TASK_SIZE / 3)
+ */
+#define TASK_UNMAPPED_BASE \
+    TARGET_PAGE_ALIGN((1ull << TARGET_VIRT_ADDR_SPACE_BITS) / 3)
+
 #include "../generic/target_mman.h"
 
 #endif
diff --git a/linux-user/nios2/target_mman.h b/linux-user/nios2/target_mman.h
index e7ba6070fe..ce18f4f871 100644
--- a/linux-user/nios2/target_mman.h
+++ b/linux-user/nios2/target_mman.h
@@ -1 +1,8 @@
+/*
+ * arch/nios2/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE         PAGE_ALIGN(TASK_SIZE / 3)
+ * TASK_SIZE                  0x7FFF0000UL
+ */
+#define TASK_UNMAPPED_BASE    TARGET_PAGE_ALIGN(0x7FFF0000 / 3)
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/openrisc/target_mman.h b/linux-user/openrisc/target_mman.h
index e7ba6070fe..f1aaad809d 100644
--- a/linux-user/openrisc/target_mman.h
+++ b/linux-user/openrisc/target_mman.h
@@ -1 +1,8 @@
+/*
+ * arch/openrisc/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE      (TASK_SIZE / 8 * 3)
+ * TASK_SIZE               (0x80000000UL)
+ */
+#define TASK_UNMAPPED_BASE      0x30000000
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/ppc/target_mman.h b/linux-user/ppc/target_mman.h
index 67cc218f2e..04f99c6077 100644
--- a/linux-user/ppc/target_mman.h
+++ b/linux-user/ppc/target_mman.h
@@ -4,6 +4,19 @@
 #define TARGET_MAP_NORESERVE            0x40
 #define TARGET_MAP_LOCKED               0x80
 
+/*
+ * arch/powerpc/include/asm/task_size_64.h
+ * TASK_UNMAPPED_BASE_USER32    (PAGE_ALIGN(TASK_SIZE_USER32 / 4))
+ * TASK_UNMAPPED_BASE_USER64    (PAGE_ALIGN(DEFAULT_MAP_WINDOW_USER64 / 4))
+ * TASK_SIZE_USER32             (0x0000000100000000UL - (1 * PAGE_SIZE))
+ * DEFAULT_MAP_WINDOW_USER64    TASK_SIZE_64TB (with 4k pages)
+ */
+#ifdef TARGET_PPC64
+#define TASK_UNMAPPED_BASE      0x0000100000000000ull
+#else
+#define TASK_UNMAPPED_BASE      0x40000000
+#endif
+
 #include "../generic/target_mman.h"
 
 #endif
diff --git a/linux-user/riscv/target_mman.h b/linux-user/riscv/target_mman.h
index e7ba6070fe..0f06dadbd4 100644
--- a/linux-user/riscv/target_mman.h
+++ b/linux-user/riscv/target_mman.h
@@ -1 +1,8 @@
+/*
+ * arch/loongarch/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE         PAGE_ALIGN(TASK_SIZE / 3)
+ */
+#define TASK_UNMAPPED_BASE \
+    TARGET_PAGE_ALIGN((1ull << (TARGET_VIRT_ADDR_SPACE_BITS - 1)) / 3)
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/s390x/target_mman.h b/linux-user/s390x/target_mman.h
index e7ba6070fe..40d149b329 100644
--- a/linux-user/s390x/target_mman.h
+++ b/linux-user/s390x/target_mman.h
@@ -1 +1,11 @@
+/*
+ * arch/s390/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE           (... : (_REGION2_SIZE >> 1))
+ *
+ * arch/s390/include/asm/pgtable.h:
+ * _REGION2_SIZE                (1UL << _REGION2_SHIFT)
+ * _REGION2_SHIFT               42
+ */
+#define TASK_UNMAPPED_BASE      (1ull << 41)
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/sh4/target_mman.h b/linux-user/sh4/target_mman.h
index e7ba6070fe..bbbc223398 100644
--- a/linux-user/sh4/target_mman.h
+++ b/linux-user/sh4/target_mman.h
@@ -1 +1,5 @@
+/* arch/sh/include/asm/processor_32.h */
+#define TASK_UNMAPPED_BASE \
+    TARGET_PAGE_ALIGN((1u << TARGET_VIRT_ADDR_SPACE_BITS) / 3)
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/sparc/target_mman.h b/linux-user/sparc/target_mman.h
index 9bad99c852..692ebf9dd7 100644
--- a/linux-user/sparc/target_mman.h
+++ b/linux-user/sparc/target_mman.h
@@ -5,6 +5,20 @@
 #define TARGET_MAP_LOCKED              0x100
 #define TARGET_MAP_GROWSDOWN           0x0200
 
+/*
+ * arch/sparc/include/asm/page_64.h:
+ * TASK_UNMAPPED_BASE      (test_thread_flag(TIF_32BIT) ? \
+ *                          _AC(0x0000000070000000,UL) : \
+ *                          VA_EXCLUDE_END)
+ * But VA_EXCLUDE_END is > 0xffff800000000000UL which doesn't work
+ * in userland emulation.
+ */
+#ifdef TARGET_ABI32
+#define TASK_UNMAPPED_BASE      0x70000000
+#else
+#define TASK_UNMAPPED_BASE      (1ull << (TARGET_VIRT_ADDR_SPACE_BITS - 2))
+#endif
+
 #include "../generic/target_mman.h"
 
 #endif
diff --git a/linux-user/user-mmap.h b/linux-user/user-mmap.h
index 2c9d99ed6c..f844ba4e61 100644
--- a/linux-user/user-mmap.h
+++ b/linux-user/user-mmap.h
@@ -18,20 +18,6 @@
 #ifndef LINUX_USER_USER_MMAP_H
 #define LINUX_USER_USER_MMAP_H
 
-#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
-#ifdef TARGET_AARCH64
-# define TASK_UNMAPPED_BASE  0x5500000000
-#else
-# define TASK_UNMAPPED_BASE  (1ul << 38)
-#endif
-#else
-#ifdef TARGET_HPPA
-# define TASK_UNMAPPED_BASE  0xfa000000
-#else
-# define TASK_UNMAPPED_BASE  0x40000000
-#endif
-#endif
-
 /*
  * Guest parameters for the ADDR_COMPAT_LAYOUT personality
  * (at present this is the only layout supported by QEMU).
diff --git a/linux-user/x86_64/target_mman.h b/linux-user/x86_64/target_mman.h
index e7ba6070fe..f9ff652b37 100644
--- a/linux-user/x86_64/target_mman.h
+++ b/linux-user/x86_64/target_mman.h
@@ -1 +1,13 @@
+/*
+ * arch/x86/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE         __TASK_UNMAPPED_BASE(TASK_SIZE_LOW)
+ * __TASK_UNMAPPED_BASE(S)    PAGE_ALIGN(S / 3)
+ *
+ * arch/x86/include/asm/page_64_types.h:
+ * TASK_SIZE_LOW              DEFAULT_MAP_WINDOW
+ * DEFAULT_MAP_WINDOW         ((1UL << 47) - PAGE_SIZE)
+ */
+#define TASK_UNMAPPED_BASE \
+    TARGET_PAGE_ALIGN((1ull << TARGET_VIRT_ADDR_SPACE_BITS) / 3)
+
 #include "../generic/target_mman.h"
diff --git a/linux-user/xtensa/target_mman.h b/linux-user/xtensa/target_mman.h
index 3933771b5b..c4f671adb7 100644
--- a/linux-user/xtensa/target_mman.h
+++ b/linux-user/xtensa/target_mman.h
@@ -14,6 +14,12 @@
 #define TARGET_MAP_STACK                0x40000
 #define TARGET_MAP_HUGETLB              0x80000
 
+/*
+ * arch/xtensa/include/asm/processor.h:
+ * TASK_UNMAPPED_BASE           (TASK_SIZE / 2)
+ */
+#define TASK_UNMAPPED_BASE      (1u << (TARGET_VIRT_ADDR_SPACE_BITS - 1))
+
 #include "../generic/target_mman.h"
 
 #endif
