exec: Fix qemu_ram_block_from_host for Xen

Since f615f39 (exec: remove ram_addr argument from
qemu_ram_block_from_host), migration under Xen is likely to fail, with a
SEGV of QEMU. But the commit only reveal a bug with the calculation of
the offset value in qemu_ram_block_from_host().

This patch calculates the offset from the ram_addr as
qemu_ram_addr_from_host() will later calculate the ram_addr from the
offset.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/exec.c b/exec.c
index a9d465b289..4f3818c561 100644
--- a/exec.c
+++ b/exec.c
@@ -1935,7 +1935,7 @@ RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
         ram_addr = xen_ram_addr_from_mapcache(ptr);
         block = qemu_get_ram_block(ram_addr);
         if (block) {
-            *offset = (host - block->host);
+            *offset = ram_addr - block->offset;
         }
         rcu_read_unlock();
         return block;