[PATCH v2 2/3] xen/x86: ensure copying to L1 guest in update_secondary_system_time()

[Haozhong Zhang <haozhong.zhang@intel.com>]

For a HVM domain, if a vcpu is in the nested guest mode,
__copy_field_to_guest() and __copy_to_guest() used by
update_secondary_system_time() will copy data to L2 guest rather than
L1 guest.

This commit temporally clears the nested guest flag before all
__copy_field_to_guest() and __copy_to_guest() in
update_secondary_system_time(), and restores the flag after those
guest copy operations.

Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Suggested-by: Jan Beulich <jbeulich@suse.com>
---
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
---
 xen/arch/x86/time.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 3ad2ab0..cb69dd5 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -24,6 +24,7 @@
 #include <xen/symbols.h>
 #include <xen/keyhandler.h>
 #include <xen/guest_access.h>
+#include <asm/hvm/nestedhvm.h>
 #include <asm/io.h>
 #include <asm/msr.h>
 #include <asm/mpspec.h>
@@ -992,10 +993,30 @@ bool_t update_secondary_system_time(struct vcpu *v,
 {
     XEN_GUEST_HANDLE(vcpu_time_info_t) user_u = v->arch.time_info_guest;
     smap_check_policy_t saved_policy;
+    bool nested_guest_mode = false;
 
     if ( guest_handle_is_null(user_u) )
         return 1;
 
+    /*
+     * Must be before all following __copy_field_to_guest() and
+     * __copy_to_guest().
+     *
+     * Otherwise, if 'v' is in the nested guest mode, paging_gva_to_gfn() called
+     * from __copy_field_to_guest() and __copy_to_guest() will treat the target
+     * address as L2 gva, and __copy_field_to_guest() and __copy_to_guest() will
+     * consequently copy runstate to L2 guest rather than L1 guest.
+     *
+     * Therefore, we clear the nested guest flag before __copy_field_to_guest()
+     * and __copy_to_guest(), and restore the flag after all guest copy.
+     */
+    if ( nestedhvm_enabled(v->domain) )
+    {
+        nested_guest_mode = nestedhvm_is_n2(v);
+        if ( nested_guest_mode )
+            nestedhvm_vcpu_exit_guestmode(v);
+    }
+
     saved_policy = smap_policy_change(v, SMAP_CHECK_ENABLED);
 
     /* 1. Update userspace version. */
@@ -1014,6 +1035,9 @@ bool_t update_secondary_system_time(struct vcpu *v,
 
     smap_policy_change(v, saved_policy);
 
+    if ( unlikely(nested_guest_mode) )
+        nestedhvm_vcpu_enter_guestmode(v);
+
     return 1;
 }
 
-- 
2.10.1


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