[Xen-devel] [PATCH v2 3/9] x86/AMD: Load context when attempting to read VPMU MSRs

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Load context (and mark it as LOADED) on any MSR access. This will allow
us to always read the most up-to-date value of an MSR: guest may write
into an MSR without enabling it (thus not marking the context as RUNNING)
and then be migrated. Without first loading the context reading this MSR
from HW will not match the pervious write since registers will not be
loaded into HW in amd_vpmu_load().

In addition, we should be saving the context when it is LOADED, not
RUNNING --- otherwise we need to save it any time it becomes non-RUNNING,
which may be a frequent occurrence.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Reviewed-by: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/svm/vpmu.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/svm/vpmu.c b/xen/arch/x86/hvm/svm/vpmu.c
index 1e54497..4be5652 100644
--- a/xen/arch/x86/hvm/svm/vpmu.c
+++ b/xen/arch/x86/hvm/svm/vpmu.c
@@ -225,6 +225,8 @@ static void amd_vpmu_restore(struct vcpu *v)
 
     context_restore(v);
     apic_write(APIC_LVTPC, ctxt->hw_lapic_lvtpc);
+
+    vpmu_set(vpmu, VPMU_CONTEXT_LOADED);
 }
 
 static inline void context_save(struct vcpu *v)
@@ -246,7 +248,7 @@ static void amd_vpmu_save(struct vcpu *v)
     struct amd_vpmu_context *ctx = vpmu->context;
 
     if ( !(vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) &&
-           vpmu_is_set(vpmu, VPMU_RUNNING)) )
+           vpmu_is_set(vpmu, VPMU_CONTEXT_LOADED)) )
         return;
 
     context_save(v);
@@ -256,6 +258,7 @@ static void amd_vpmu_save(struct vcpu *v)
 
     ctx->hw_lapic_lvtpc = apic_read(APIC_LVTPC);
     apic_write(APIC_LVTPC,  ctx->hw_lapic_lvtpc | APIC_LVT_MASKED);
+    vpmu_reset(vpmu, VPMU_CONTEXT_LOADED);
 }
 
 static void context_update(unsigned int msr, u64 msr_content)
@@ -318,6 +321,12 @@ static int amd_vpmu_do_wrmsr(unsigned int msr, uint64_t 
msr_content)
         release_pmu_ownship(PMU_OWNER_HVM);
     }
 
+    if ( !vpmu_is_set(vpmu, VPMU_CONTEXT_LOADED) )
+    {
+        context_restore(v);
+        vpmu_set(vpmu, VPMU_CONTEXT_LOADED);
+    }
+
     /* Update vpmu context immediately */
     context_update(msr, msr_content);
 
@@ -328,7 +337,17 @@ static int amd_vpmu_do_wrmsr(unsigned int msr, uint64_t 
msr_content)
 
 static int amd_vpmu_do_rdmsr(unsigned int msr, uint64_t *msr_content)
 {
+    struct vcpu *v = current;
+    struct vpmu_struct *vpmu = vcpu_vpmu(v);
+
+    if ( !vpmu_is_set(vpmu, VPMU_CONTEXT_LOADED) )
+    {
+        context_restore(v);
+        vpmu_set(vpmu, VPMU_CONTEXT_LOADED);
+    }
+
     rdmsrl(msr, *msr_content);
+
     return 1;
 }
 
-- 
1.8.1.2


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