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[Xen-changelog] [xen master] x86: handle resumed instruction based on previous mem_event reply



commit 1e71f2d7418dfdcf6356e4be8e9311ea607a1877
Author:     Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
AuthorDate: Thu Sep 18 14:57:45 2014 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Sep 18 14:57:45 2014 +0200

    x86: handle resumed instruction based on previous mem_event reply
    
    In a scenario where a page fault that triggered a mem_event occured,
    p2m_mem_access_check() will now be able to either 1) emulate the
    current instruction, or 2) emulate it, but don't allow it to perform
    any writes.
    
    Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
    Acked-by: Tim Deegan <tim@xxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/domain.c          |    3 ++
 xen/arch/x86/mm/p2m.c          |   75 ++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-x86/domain.h   |   11 ++++++
 xen/include/public/mem_event.h |   21 ++++++++---
 4 files changed, 105 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index f7e0e78..7b1dfe6 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -415,6 +415,9 @@ int vcpu_initialise(struct vcpu *v)
 
     v->arch.flags = TF_kernel_mode;
 
+    /* By default, do not emulate */
+    v->arch.mem_event.emulate_flags = 0;
+
     rc = mapcache_vcpu_init(v);
     if ( rc )
         return rc;
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 7587797..54859c8 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1395,6 +1395,7 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned long 
gla,
     p2m_access_t p2ma;
     mem_event_request_t *req;
     int rc;
+    unsigned long eip = guest_cpu_user_regs()->eip;
 
     /* First, handle rx2rw conversion automatically.
      * These calls to p2m->set_entry() must succeed: we have the gfn
@@ -1448,6 +1449,30 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned long 
gla,
         }
     }
 
+    /* The previous mem_event reply does not match the current state. */
+    if ( v->arch.mem_event.gpa != gpa || v->arch.mem_event.eip != eip )
+    {
+        /* Don't emulate the current instruction, send a new mem_event. */
+        v->arch.mem_event.emulate_flags = 0;
+
+        /*
+         * Make sure to mark the current state to match it again against
+         * the new mem_event about to be sent.
+         */
+        v->arch.mem_event.gpa = gpa;
+        v->arch.mem_event.eip = eip;
+    }
+
+    if ( v->arch.mem_event.emulate_flags )
+    {
+        hvm_mem_event_emulate_one((v->arch.mem_event.emulate_flags &
+                                   MEM_EVENT_FLAG_EMULATE_NOWRITE) != 0,
+                                  TRAP_invalid_op, HVM_DELIVER_NO_ERROR_CODE);
+
+        v->arch.mem_event.emulate_flags = 0;
+        return 1;
+    }
+
     *req_ptr = NULL;
     req = xzalloc(mem_event_request_t);
     if ( req )
@@ -1502,6 +1527,56 @@ void p2m_mem_access_resume(struct domain *d)
 
         v = d->vcpu[rsp.vcpu_id];
 
+        /* Mark vcpu for skipping one instruction upon rescheduling. */
+        if ( rsp.flags & MEM_EVENT_FLAG_EMULATE )
+        {
+            xenmem_access_t access;
+            bool_t violation = 1;
+
+            if ( p2m_get_mem_access(d, rsp.gfn, &access) == 0 )
+            {
+                switch ( access )
+                {
+                case XENMEM_access_n:
+                case XENMEM_access_n2rwx:
+                default:
+                    violation = rsp.access_r || rsp.access_w || rsp.access_x;
+                    break;
+
+                case XENMEM_access_r:
+                    violation = rsp.access_w || rsp.access_x;
+                    break;
+
+                case XENMEM_access_w:
+                    violation = rsp.access_r || rsp.access_x;
+                    break;
+
+                case XENMEM_access_x:
+                    violation = rsp.access_r || rsp.access_w;
+                    break;
+
+                case XENMEM_access_rx:
+                case XENMEM_access_rx2rw:
+                    violation = rsp.access_w;
+                    break;
+
+                case XENMEM_access_wx:
+                    violation = rsp.access_r;
+                    break;
+
+                case XENMEM_access_rw:
+                    violation = rsp.access_x;
+                    break;
+
+                case XENMEM_access_rwx:
+                    violation = 0;
+                    break;
+                }
+            }
+
+            v->arch.mem_event.emulate_flags = violation ? rsp.flags : 0;
+        }
+
         /* Unpause domain */
         if ( rsp.flags & MEM_EVENT_FLAG_VCPU_PAUSED )
             mem_event_vcpu_unpause(v);
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 8fc5a45..7abe1b3 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -459,6 +459,17 @@ struct arch_vcpu
 
     /* A secondary copy of the vcpu time info. */
     XEN_GUEST_HANDLE(vcpu_time_info_t) time_info_guest;
+
+    /*
+     * Should we emulate the next matching instruction on VCPU resume
+     * after a mem_event?
+     */
+    struct {
+        uint32_t emulate_flags;
+        unsigned long gpa;
+        unsigned long eip;
+    } mem_event;
+
 } __cacheline_aligned;
 
 smap_check_policy_t smap_policy_change(struct vcpu *v,
diff --git a/xen/include/public/mem_event.h b/xen/include/public/mem_event.h
index d3dd9c6..599f9e8 100644
--- a/xen/include/public/mem_event.h
+++ b/xen/include/public/mem_event.h
@@ -31,11 +31,22 @@
 #include "io/ring.h"
 
 /* Memory event flags */
-#define MEM_EVENT_FLAG_VCPU_PAUSED  (1 << 0)
-#define MEM_EVENT_FLAG_DROP_PAGE    (1 << 1)
-#define MEM_EVENT_FLAG_EVICT_FAIL   (1 << 2)
-#define MEM_EVENT_FLAG_FOREIGN      (1 << 3)
-#define MEM_EVENT_FLAG_DUMMY        (1 << 4)
+#define MEM_EVENT_FLAG_VCPU_PAUSED     (1 << 0)
+#define MEM_EVENT_FLAG_DROP_PAGE       (1 << 1)
+#define MEM_EVENT_FLAG_EVICT_FAIL      (1 << 2)
+#define MEM_EVENT_FLAG_FOREIGN         (1 << 3)
+#define MEM_EVENT_FLAG_DUMMY           (1 << 4)
+/*
+ * Emulate the fault-causing instruction (if set in the event response flags).
+ * This will allow the guest to continue execution without lifting the page
+ * access restrictions.
+ */
+#define MEM_EVENT_FLAG_EMULATE         (1 << 5)
+/*
+ * Same as MEM_EVENT_FLAG_EMULATE, but with write operations or operations
+ * potentially having side effects (like memory mapped or port I/O) disabled.
+ */
+#define MEM_EVENT_FLAG_EMULATE_NOWRITE (1 << 6)
 
 /* Reasons for the memory event request */
 #define MEM_EVENT_REASON_UNKNOWN     0    /* typical reason */
--
generated by git-patchbot for /home/xen/git/xen.git#master

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