[Xen-changelog] [xen master] x86: disable emulate.c REP optimization if introspection is active

[patchbot@xxxxxxx]

commit 413e9215ace59eb9d0dcbd00376e1029ec23c6ab
Author:     Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
AuthorDate: Tue Nov 4 13:13:55 2014 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Nov 4 13:13:55 2014 +0100

    x86: disable emulate.c REP optimization if introspection is active
    
    Emulation for REP instructions is optimized to perform a single
    write for all repeats in the current page if possible. However,
    this interferes with a memory introspection application's ability
    to detect suspect behaviour, since it will cause only one
    mem_event to be sent per page touched.
    This patch disables the optimization, gated on introspection
    being active for the domain.
    
    Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/emulate.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index c0f47d2..14c1847 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -406,8 +406,13 @@ static int hvmemul_virtual_to_linear(
      * Clip repetitions to avoid overflow when multiplying by @bytes_per_rep.
      * The chosen maximum is very conservative but it's what we use in
      * hvmemul_linear_to_phys() so there is no point in using a larger value.
+     * If introspection has been enabled for this domain, *reps should be
+     * at most 1, since optimization might otherwise cause a single mem_event
+     * being triggered for repeated writes to a whole page.
      */
-    *reps = min_t(unsigned long, *reps, 4096);
+    *reps = min_t(unsigned long, *reps,
+                  
unlikely(current->domain->arch.hvm_domain.introspection_enabled)
+                           ? 1 : 4096);
 
     reg = hvmemul_get_seg_reg(seg, hvmemul_ctxt);
 
--
generated by git-patchbot for /home/xen/git/xen.git#master

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