[kvm-unit-tests PATCH v2 1/4] lib/alloc_page: Zero allocated pages

nadav.amit
2019-05-03T17:54:38Z

One of the most important properties of tests is reproducibility. For
tests to be reproducible, the same environment should be set on each
test invocation.

When it comes to memory content, this is not exactly the case in
kvm-unit-tests. The tests might, mistakenly or intentionally, assume
that memory is zeroed (by the BIOS or KVM). However, failures might not
be reproducible if this assumption is broken.

As an example, consider x86 do_iret(), which mistakenly does not push
SS:RSP onto the stack on 64-bit mode, although they are popped
unconditionally on iret.

Do not assume that memory is zeroed. Clear it once it is allocated to
allow tests to easily be reproduced.

Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
---
lib/alloc_page.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/lib/alloc_page.c b/lib/alloc_page.c
index 730f2b5..97d1339 100644
--- a/lib/alloc_page.c
+++ b/lib/alloc_page.c
@@ -65,6 +65,8 @@ void *alloc_page()
freelist = *(void **)freelist;
spin_unlock(&lock);

+ if (p)
+ memset(p, 0, PAGE_SIZE);
return p;
}

@@ -126,6 +128,8 @@ void *alloc_pages(unsigned long order)
}
}
spin_unlock(&lock);
+ if (run_start)
+ memset(run_start, 0, n * PAGE_SIZE);
return run_start;
}

--
2.17.1