[Xen-devel] [PATCH for-4.13 v3 1/2] x86/vmx: add ASSERT to prevent syncing PIR to IRR...

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

... if the vCPU is different than the one currently running or if it's
not paused. Note that syncing PIR to IRR when the vCPU is running is
not allowed, since the hardware is in control of VMCS IRR field.

Allow syncing PIR to IRR when the vCPU is paused, this is required in
order to save the local APIC state.

No functional change intended.

Suggested by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Juergen Gross <jgross@xxxxxxxx>
---
Changes since v2:
 - Only allow syncing if the vCPU is the current one or if it's
   paused.

Changes since v1:
 - Use vcpu_runnable instead of is_running.
---
 xen/arch/x86/hvm/vmx/vmx.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index a55ff37733..c817aec75d 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2054,6 +2054,19 @@ static void vmx_sync_pir_to_irr(struct vcpu *v)
     unsigned int group, i;
     DECLARE_BITMAP(pending_intr, NR_VECTORS);
 
+    if ( v != current && !atomic_read(&v->pause_count) )
+    {
+        /*
+         * Syncing PIR to IRR must not be done behind the back of the CPU,
+         * since the IRR is controlled by the hardware when the vCPU is
+         * executing. Only allow Xen to do such sync if the vCPU is the current
+         * one or if it's paused: that's required in order to sync the lapic
+         * state before saving it.
+         */
+        ASSERT_UNREACHABLE();
+        return;
+    }
+
     if ( !pi_test_and_clear_on(&v->arch.hvm.vmx.pi_desc) )
         return;
 
-- 
2.24.0


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