[Xen-devel] [PATCH v6 2/4] x86/hvm: Treat non-instruction fetch nested page faults also as read violations

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

As pointed out by Jan Beulich in 
http://lists.xen.org/archives/html/xen-devel/2014-08/msg01269.html: 
"Read-modify-write instructions absolutely need to be treated as read accesses, 
yet hardware doesn't guarantee to tell us so (they may surface as just write 
accesses)." This patch addresses the issue in both the VMX and the SVM side.

VMX: Treat all non-instruction fetch violations as read violations (in addition 
to those that were already reported as read violations).
SVM: Refine the handling to distinguish between read/write and instruction 
fetch access violations.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
---
 xen/arch/x86/hvm/svm/svm.c | 2 +-
 xen/arch/x86/hvm/vmx/vmx.c | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 1f72e19..9531248 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1404,7 +1404,7 @@ static void svm_do_nested_pgfault(struct vcpu *v,
     struct p2m_domain *p2m = NULL;
 
     struct npfec npfec = {
-        .read_access = 1, /* All NPFs count as reads */
+        .read_access = !(pfec & PFEC_insn_fetch),
         .write_access = !!(pfec & PFEC_write_access),
         .insn_fetch = !!(pfec & PFEC_insn_fetch)
     };
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 656ce61..af0ad7c 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2354,7 +2354,8 @@ static void ept_handle_violation(unsigned long 
qualification, paddr_t gpa)
     int ret;
     struct domain *d = current->domain;
     struct npfec npfec = {
-        .read_access = !!(qualification & EPT_READ_VIOLATION),
+        .read_access = !!(qualification & EPT_READ_VIOLATION) ||
+                        !(qualification & EPT_EXEC_VIOLATION),
         .write_access = !!(qualification & EPT_WRITE_VIOLATION),
         .insn_fetch = !!(qualification & EPT_EXEC_VIOLATION)
     };
-- 
2.0.1


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