accel/tcg: Relax va restrictions on 64-bit guests

We cannot at present limit a 64-bit guest to a virtual address
space smaller than the host.  It will mostly work to ignore this
limitation, except if the guest uses high bits of the address
space for tags.  But it will certainly work better, as presently
we can wind up failing to allocate the guest stack.

Widen our user-only page tree to the host or abi pointer width.
Remove the workaround for this problem from target/alpha.
Always validate guest addresses vs reserved_va, as there we
control allocation ourselves.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

Message-Id: <20200513175134.19619-7-alex.bennee@linaro.org>

include/exec/cpu-all.h

@@ -162,12 +162,27 @@ extern unsigned long guest_base;
 extern bool have_guest_base;
 extern unsigned long reserved_va;
 
-#if HOST_LONG_BITS <= TARGET_VIRT_ADDR_SPACE_BITS
-#define GUEST_ADDR_MAX (~0ul)
+/*
+ * Limit the guest addresses as best we can.
+ *
+ * When not using -R reserved_va, we cannot really limit the guest
+ * to less address space than the host.  For 32-bit guests, this
+ * acts as a sanity check that we're not giving the guest an address
+ * that it cannot even represent.  For 64-bit guests... the address
+ * might not be what the real kernel would give, but it is at least
+ * representable in the guest.
+ *
+ * TODO: Improve address allocation to avoid this problem, and to
+ * avoid setting bits at the top of guest addresses that might need
+ * to be used for tags.
+ */
+#if MIN(TARGET_VIRT_ADDR_SPACE_BITS, TARGET_ABI_BITS) <= 32
+# define GUEST_ADDR_MAX_  UINT32_MAX
 #else
-#define GUEST_ADDR_MAX (reserved_va ? reserved_va - 1 : \
-                                    (1ul << TARGET_VIRT_ADDR_SPACE_BITS) - 1)
+# define GUEST_ADDR_MAX_  (~0ul)
 #endif
+#define GUEST_ADDR_MAX    (reserved_va ? reserved_va - 1 : GUEST_ADDR_MAX_)
+
 #else
 
 #include "exec/hwaddr.h"