[Xen-devel] [PATCH v13 for-xen-4.5 02/21] x86/VPMU: Manage VPMU_CONTEXT_SAVE flag in vpmu_save_force()

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

There is a possibility that we set VPMU_CONTEXT_SAVE on VPMU context in
vpmu_load() and never clear it (because vpmu_save_force() will see
VPMU_CONTEXT_LOADED bit clear, which is possible on AMD processors)

The problem is that amd_vpmu_save() assumes that if VPMU_CONTEXT_SAVE is set
then (1) we need to save counters and (2) we don't need to "stop" control
registers since they must have been stopped earlier. The latter may cause all
sorts of problem (like counters still running in a wrong guest and hypervisor
sending to that guest unexpected PMU interrupts).

Since setting this flag is currently always done prior to calling
vpmu_save_force() let's both set and clear it there.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Reviewed-by: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vpmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/vpmu.c b/xen/arch/x86/hvm/vpmu.c
index 15d5b6f..451b346 100644
--- a/xen/arch/x86/hvm/vpmu.c
+++ b/xen/arch/x86/hvm/vpmu.c
@@ -130,6 +130,8 @@ static void vpmu_save_force(void *arg)
     if ( !vpmu_is_set(vpmu, VPMU_CONTEXT_LOADED) )
         return;
 
+    vpmu_set(vpmu, VPMU_CONTEXT_SAVE);
+
     if ( vpmu->arch_vpmu_ops )
         (void)vpmu->arch_vpmu_ops->arch_vpmu_save(v);
 
@@ -178,7 +180,6 @@ void vpmu_load(struct vcpu *v)
          */
         if ( vpmu_is_set(vpmu, VPMU_CONTEXT_LOADED) )
         {
-            vpmu_set(vpmu, VPMU_CONTEXT_SAVE);
             on_selected_cpus(cpumask_of(vpmu->last_pcpu),
                              vpmu_save_force, (void *)v, 1);
             vpmu_reset(vpmu, VPMU_CONTEXT_LOADED);
@@ -195,7 +196,6 @@ void vpmu_load(struct vcpu *v)
         vpmu = vcpu_vpmu(prev);
 
         /* Someone ran here before us */
-        vpmu_set(vpmu, VPMU_CONTEXT_SAVE);
         vpmu_save_force(prev);
         vpmu_reset(vpmu, VPMU_CONTEXT_LOADED);
 
-- 
1.8.1.4


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