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From e688bfbda0f6893b08d1e51f4fb26d4b38e922d4 Mon Sep 17 00:00:00 2001
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From: Christian Borntraeger <borntraeger@de.ibm.com>
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Date: Fri, 10 Aug 2012 15:11:45 +0200
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Subject: [PATCH] qemu: Use valgrind annotations to mark kvm guest memory as
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defined
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valgrind with kvm produces a big amount of false positives regarding
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"Conditional jump or move depends on uninitialised value(s)". This
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happens because the guest memory is allocated with qemu_vmalloc which
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boils down posix_memalign etc. This function is (correctly) considered
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by valgrind as returning undefined memory.
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Since valgrind is based on jitting code, it will not be able to see
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changes made by the guest to guest memory if this is done by KVM_RUN,
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thus keeping most of the guest memory undefined.
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Now lots of places in qemu will then use guest memory to change behaviour.
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To avoid the flood of these messages, lets declare the whole guest
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memory as defined. This will reduce the noise and allows us to see real
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problems.
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In the future we might want to make this conditional, since there
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is actually something that we can use those false positives for:
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These messages will point to code that depends on guest memory, so
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we can use these backtraces to actually make an audit that is focussed
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only at those code places. For normal development we dont want to
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see those messages, though.
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Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
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Signed-off-by: Avi Kivity <avi@redhat.com>
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(cherry picked from commit 62fe83318d2fc5b31f473d66326910d94c1c4907)
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Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
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---
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configure | 3 ++-
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kvm-all.c | 7 +++++++
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2 files changed, 9 insertions(+), 1 deletion(-)
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diff --git a/configure b/configure
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index d7a948f..8874eff 100755
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--- a/configure
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+++ b/configure
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@@ -2937,11 +2937,12 @@ if compile_prog "-Werror" "" ; then
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fi
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########################################
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-# check if we have valgrind/valgrind.h
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+# check if we have valgrind/valgrind.h and valgrind/memcheck.h
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valgrind_h=no
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cat > $TMPC << EOF
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#include <valgrind/valgrind.h>
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+#include <valgrind/memcheck.h>
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int main(void) {
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return 0;
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}
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diff --git a/kvm-all.c b/kvm-all.c
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index badf1d8..90c71f9 100644
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--- a/kvm-all.c
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+++ b/kvm-all.c
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@@ -39,6 +39,10 @@
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#include <sys/eventfd.h>
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#endif
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+#ifdef CONFIG_VALGRIND_H
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+#include <valgrind/memcheck.h>
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+#endif
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+
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/* KVM uses PAGE_SIZE in its definition of COALESCED_MMIO_MAX */
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#define PAGE_SIZE TARGET_PAGE_SIZE
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@@ -1769,6 +1773,9 @@ void *kvm_vmalloc(ram_addr_t size)
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void kvm_setup_guest_memory(void *start, size_t size)
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{
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+#ifdef CONFIG_VALGRIND_H
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+ VALGRIND_MAKE_MEM_DEFINED(start, size);
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+#endif
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if (!kvm_has_sync_mmu()) {
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int ret = qemu_madvise(start, size, QEMU_MADV_DONTFORK);
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--
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1.7.12.1
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