[Xen-devel] [PATCH for-4.13] x86/tsc: update vcpu time info on guest TSC adjustments

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

If a HVM/PVH guest writes to MSR_IA32_TSC{_ADJUST} and thus changes
the value of the time stamp counter the vcpu time info must also be
updated, or the time calculated by the guest using the Xen PV clock
interface will be skewed.

Update the vcpu time info when the guest writes to either MSR_IA32_TSC
or MSR_IA32_TSC_ADJUST. This fixes lockups seen when running the
pv-shim on AMD hardware, since the shim will aggressively try to keep
TSCs in sync by periodically writing to MSR_IA32_TSC if the TSC is not
reliable.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Jürgen Groß <jgross@xxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 9acd359c99..e4c0425330 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -442,6 +442,8 @@ static void hvm_set_guest_tsc_msr(struct vcpu *v, u64 
guest_tsc)
 
     hvm_set_guest_tsc(v, guest_tsc);
     v->arch.hvm.msr_tsc_adjust += v->arch.hvm.cache_tsc_offset - tsc_offset;
+    if ( v == current )
+        update_vcpu_system_time(v);
 }
 
 static void hvm_set_guest_tsc_adjust(struct vcpu *v, u64 tsc_adjust)
@@ -449,6 +451,8 @@ static void hvm_set_guest_tsc_adjust(struct vcpu *v, u64 
tsc_adjust)
     v->arch.hvm.cache_tsc_offset += tsc_adjust - v->arch.hvm.msr_tsc_adjust;
     hvm_set_tsc_offset(v, v->arch.hvm.cache_tsc_offset, 0);
     v->arch.hvm.msr_tsc_adjust = tsc_adjust;
+    if ( v == current )
+        update_vcpu_system_time(v);
 }
 
 u64 hvm_get_guest_tsc_fixed(struct vcpu *v, uint64_t at_tsc)
-- 
2.23.0


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