[xen master] x86/viridian: EOI MSR should always happen in affected vCPU context

[patchbot@xxxxxxx]

commit b8428a858aba2200abe83afa1eb7c8115979c509
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Jan 11 11:42:49 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jan 11 11:42:49 2022 +0100

    x86/viridian: EOI MSR should always happen in affected vCPU context
    
    The HV_X64_MSR_EOI wrmsr should always happen with the target vCPU
    as current, as there's no support for EOI'ing interrupts on a remote
    vCPU.
    
    While there also turn the unconditional assert at the top of the
    function into an error on non-debug builds.
    
    No functional change intended.
    
    Requested-by: Jan Beulich <jbeulich@xxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/hvm/viridian/synic.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/viridian/synic.c 
b/xen/arch/x86/hvm/viridian/synic.c
index 22e2df27e5..e18538c60a 100644
--- a/xen/arch/x86/hvm/viridian/synic.c
+++ b/xen/arch/x86/hvm/viridian/synic.c
@@ -79,11 +79,20 @@ int viridian_synic_wrmsr(struct vcpu *v, uint32_t idx, 
uint64_t val)
     struct viridian_vcpu *vv = v->arch.hvm.viridian;
     struct domain *d = v->domain;
 
-    ASSERT(v == current || !v->is_running);
+    if ( v != current && v->is_running )
+    {
+        ASSERT_UNREACHABLE();
+        return X86EMUL_EXCEPTION;
+    }
 
     switch ( idx )
     {
     case HV_X64_MSR_EOI:
+        if ( v != current )
+        {
+            ASSERT_UNREACHABLE();
+            return X86EMUL_EXCEPTION;
+        }
         vlapic_EOI_set(vcpu_vlapic(v));
         break;
 
--
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