[Xen-changelog] [xen master] add update indicator to vcpu_runstate_info

[patchbot@xxxxxxx]

commit 2529c850ea48f036727ca2f148caed89391311b8
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue Jun 21 12:03:02 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 21 12:03:02 2016 +0200

    add update indicator to vcpu_runstate_info
    
    There has been a report about incorrect vruntime accounting in Linux
    guests under Xen. A Linux kernel with CONFIG_PARAVIRT_TIME_ACCOUNTING
    set is capable to do correct vruntime accounting, but this would
    require the kernel to be able to read the runstate data of other cpus.
    
    A guest mapping vcpu_runstate_info into its memory can't read this
    information from another cpu but the one the data is referring to.
    Reason is there is no reliable way for the guest to detect a concurrent
    data update by the hypervisor. In order to support reading another
    vcpu's mapped vcpu_runstate_info an indicator for an occurring update
    of the runstate information is needed.
    
    Add the possibility to activate setting this indicator in the highest
    bit of state_entry_time via a vm_assist hypercall. When activated the
    update indicator will be set before the runstate information is
    modified in guest memory and it will be reset after modification is
    done. As state_entry_time is guaranteed to be different after each
    update the guest can detect any update (either in progress or while
    reading the runstate data) by comparing state_entry_time before and
    after reading runstate data: in case the values differ or the update
    indicator was set the data might be inconsistent and should be reread.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/arm/domain.c        | 20 ++++++++++++++++++++
 xen/arch/x86/domain.c        | 21 +++++++++++++++++++++
 xen/include/asm-arm/config.h |  2 +-
 xen/include/asm-x86/config.h |  1 +
 xen/include/public/vcpu.h    |  6 ++++++
 xen/include/public/xen.h     |  7 +++++++
 6 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 1365b4a..d8a804c 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -239,10 +239,30 @@ static void ctxt_switch_to(struct vcpu *n)
 /* Update per-VCPU guest runstate shared memory area (if registered). */
 static void update_runstate_area(struct vcpu *v)
 {
+    void __user *guest_handle = NULL;
+
     if ( guest_handle_is_null(runstate_guest(v)) )
         return;
 
+    if ( VM_ASSIST(v->domain, runstate_update_flag) )
+    {
+        guest_handle = &v->runstate_guest.p->state_entry_time + 1;
+        guest_handle--;
+        v->runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
+        __raw_copy_to_guest(guest_handle,
+                            (void *)(&v->runstate.state_entry_time + 1) - 1, 
1);
+        smp_wmb();
+    }
+
     __copy_to_guest(runstate_guest(v), &v->runstate, 1);
+
+    if ( guest_handle )
+    {
+        v->runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
+        smp_wmb();
+        __raw_copy_to_guest(guest_handle,
+                            (void *)(&v->runstate.state_entry_time + 1) - 1, 
1);
+    }
 }
 
 static void schedule_tail(struct vcpu *prev)
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 989bc74..3ba7ed1 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1926,12 +1926,25 @@ bool_t update_runstate_area(struct vcpu *v)
 {
     bool_t rc;
     smap_check_policy_t smap_policy;
+    void __user *guest_handle = NULL;
 
     if ( guest_handle_is_null(runstate_guest(v)) )
         return 1;
 
     smap_policy = smap_policy_change(v, SMAP_CHECK_ENABLED);
 
+    if ( VM_ASSIST(v->domain, runstate_update_flag) )
+    {
+        guest_handle = has_32bit_shinfo(v->domain)
+            ? &v->runstate_guest.compat.p->state_entry_time + 1
+            : &v->runstate_guest.native.p->state_entry_time + 1;
+        guest_handle--;
+        v->runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
+        __raw_copy_to_guest(guest_handle,
+                            (void *)(&v->runstate.state_entry_time + 1) - 1, 
1);
+        smp_wmb();
+    }
+
     if ( has_32bit_shinfo(v->domain) )
     {
         struct compat_vcpu_runstate_info info;
@@ -1944,6 +1957,14 @@ bool_t update_runstate_area(struct vcpu *v)
         rc = __copy_to_guest(runstate_guest(v), &v->runstate, 1) !=
              sizeof(v->runstate);
 
+    if ( guest_handle )
+    {
+        v->runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
+        smp_wmb();
+        __raw_copy_to_guest(guest_handle,
+                            (void *)(&v->runstate.state_entry_time + 1) - 1, 
1);
+    }
+
     smap_policy_change(v, smap_policy);
 
     return rc;
diff --git a/xen/include/asm-arm/config.h b/xen/include/asm-arm/config.h
index 4e7d20e..9417be6 100644
--- a/xen/include/asm-arm/config.h
+++ b/xen/include/asm-arm/config.h
@@ -199,7 +199,7 @@ extern unsigned long frametable_virt_end;
 #define watchdog_disable() ((void)0)
 #define watchdog_enable()  ((void)0)
 
-#define VM_ASSIST_VALID          (0)
+#define VM_ASSIST_VALID          (1UL << VMASST_TYPE_runstate_update_flag)
 
 #endif /* __ARM_CONFIG_H__ */
 /*
diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
index c10129d..6fd84e7 100644
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -332,6 +332,7 @@ extern unsigned long xen_phys_start;
                                   (1UL << VMASST_TYPE_writable_pagetables) | \
                                   (1UL << VMASST_TYPE_pae_extended_cr3)    | \
                                   (1UL << VMASST_TYPE_architectural_iopl)  | \
+                                  (1UL << VMASST_TYPE_runstate_update_flag)| \
                                   (1UL << VMASST_TYPE_m2p_strict))
 #define VM_ASSIST_VALID          NATIVE_VM_ASSIST_VALID
 #define COMPAT_VM_ASSIST_VALID   (NATIVE_VM_ASSIST_VALID & \
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index 692b87a..2aa230d 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -84,6 +84,12 @@ struct vcpu_runstate_info {
     /* When was current state entered (system time, ns)? */
     uint64_t state_entry_time;
     /*
+     * Update indicator set in state_entry_time:
+     * When activated via VMASST_TYPE_runstate_update_flag, set during
+     * updates in guest memory mapped copy of vcpu_runstate_info.
+     */
+#define XEN_RUNSTATE_UPDATE          (1ULL << 63)
+    /*
      * Time spent in each RUNSTATE_* (ns). The sum of these times is
      * guaranteed not to drift from system time.
      */
diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index 37bbb22..b9e5e0f 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -510,6 +510,13 @@ DEFINE_XEN_GUEST_HANDLE(mmuext_op_t);
 #define VMASST_TYPE_architectural_iopl   4
 
 /*
+ * All guests: activate update indicator in vcpu_runstate_info
+ * Enable setting the XEN_RUNSTATE_UPDATE flag in guest memory mapped
+ * vcpu_runstate_info during updates of the runstate information.
+ */
+#define VMASST_TYPE_runstate_update_flag 5
+
+/*
  * x86/64 guests: strictly hide M2P from user mode.
  * This allows the guest to control respective hypervisor behavior:
  * - when not set, L4 tables get created with the respective slot blank,
--
generated by git-patchbot for /home/xen/git/xen.git#master

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