[Qemu-devel] [PATCH 2/5] linux-user: Introduce qemu_vmalloc_guest_safe

[Jan Kiszka]

Add qemu_vmalloc_guest_safe to allocate memory from a region that are
reachable by user-space guests. Addresses returned by this function can
safely be provided to h2g.

Signed-off-by: Jan Kiszka <address@hidden>
---
 linux-user/mmap.c |   39 +++++++++++++++++++++++++++++++++++++++
 linux-user/qemu.h |    1 +
 2 files changed, 40 insertions(+)

Index: b/linux-user/mmap.c
===================================================================
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -94,6 +94,45 @@ void *qemu_vmalloc(size_t size)
     return p;
 }
 
+static abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size);
+
+void *qemu_vmalloc_guest_safe(size_t size)
+{
+#if TARGET_LONG_BIT < HOST_LONG_BITS
+    void *p;
+    unsigned long addr;
+    abi_ulong guest_start;
+
+    mmap_lock();
+
+    /* Ensure we allocate from the guest-reachable rage */
+    size = HOST_PAGE_ALIGN(size);
+    guest_start = mmap_find_vma(0, size);
+    if (guest_start == (abi_ulong)-1) {
+        p = NULL;
+        goto unlock_exit;
+    }
+
+    /* Use map and mark the pages as used.  */
+    p = mmap(g2h(guest_start), size, PROT_READ | PROT_WRITE,
+             MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (p == MAP_FAILED) {
+        p = NULL;
+        goto unlock_exit;
+    }
+
+    addr = (unsigned long)p;
+    page_set_flags(addr & TARGET_PAGE_MASK, TARGET_PAGE_ALIGN(addr + size),
+                   PAGE_RESERVED);
+
+unlock_exit:
+    mmap_unlock();
+    return p;
+#else
+    return qemu_vmalloc(size);
+#endif
+}
+
 void *qemu_malloc(size_t size)
 {
     char * p;
Index: b/linux-user/qemu.h
===================================================================
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -247,6 +247,7 @@ void mmap_unlock(void);
 void mmap_fork_start(void);
 void mmap_fork_end(int child);
 #endif
+void *qemu_vmalloc_guest_safe(size_t size);
 
 /* user access */