linux-user: resolve reserved_va vma downwards

After consulting with Paul Brook, we concluded that it's best to search
the VMA space downwards, so that we don't even get the chance to conflict
with the brk range.

This patch resolves a bunch of allocation conflicts when using -R.
Signed-off-by: NAlexander Graf <agraf@suse.de>
[minor changes to get it to apply -- PMM]
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>

linux-user/main.c

@@ -3420,6 +3420,7 @@ int main(int argc, char **argv, char **envp)
             guest_base = HOST_PAGE_ALIGN((unsigned long)p);
         }
         qemu_log("Reserved 0x%lx bytes of guest address space\n", reserved_va);
+        mmap_next_start = reserved_va;
     }
 
     if (reserved_va || have_guest_base) {

linux-user/mmap.c

@@ -212,7 +212,7 @@ static int mmap_frag(abi_ulong real_start,
 #else
 # define TASK_UNMAPPED_BASE  0x40000000
 #endif
-static abi_ulong mmap_next_start = TASK_UNMAPPED_BASE;
+abi_ulong mmap_next_start = TASK_UNMAPPED_BASE;
 
 unsigned long last_brk;
 
@@ -222,7 +222,7 @@ unsigned long last_brk;
 static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size)
 {
     abi_ulong addr;
-    abi_ulong last_addr;
+    abi_ulong end_addr;
     int prot;
     int looped = 0;
 
@@ -230,25 +230,38 @@ static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size)
         return (abi_ulong)-1;
     }
 
-    last_addr = start;
-    for (addr = start; last_addr + size != addr; addr += qemu_host_page_size) {
-        if (last_addr + size >= RESERVED_VA
-            || (abi_ulong)(last_addr + size) < last_addr) {
+    size = HOST_PAGE_ALIGN(size);
+    end_addr = start + size;
+    if (end_addr > RESERVED_VA) {
+        end_addr = RESERVED_VA;
+    }
+    addr = end_addr - qemu_host_page_size;
+
+    while (1) {
+        if (addr > end_addr) {
             if (looped) {
                 return (abi_ulong)-1;
             }
-            last_addr = qemu_host_page_size;
-            addr = 0;
+            end_addr = RESERVED_VA;
+            addr = end_addr - qemu_host_page_size;
             looped = 1;
             continue;
         }
         prot = page_get_flags(addr);
         if (prot) {
-            last_addr = addr + qemu_host_page_size;
+            end_addr = addr;
+        }
+        if (addr + size == end_addr) {
+            break;
         }
+        addr -= qemu_host_page_size;
+    }
+
+    if (start == mmap_next_start) {
+        mmap_next_start = addr;
     }
-    mmap_next_start = addr;
-    return last_addr;
+
+    return addr;
 }
 #endif
 

linux-user/qemu.h

@@ -251,6 +251,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
                        abi_ulong new_addr);
 int target_msync(abi_ulong start, abi_ulong len, int flags);
 extern unsigned long last_brk;
+extern abi_ulong mmap_next_start;
 void mmap_lock(void);
 void mmap_unlock(void);
 abi_ulong mmap_find_vma(abi_ulong, abi_ulong);