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[Xen-devel] [PATCH] [RFC] iommu/crash: Interrupt remapping is also disabled on crash

On the crash path in nmi_shootdown_cpus(), we shut down the IOMMU, then
disable the IOAPIC.

On systems which support interrupt remapping, the variable iommu_intremap
remains set, meaning that disable_IO_APIC() issues interrupt remapping
invalidate requests.

Pre Sandy-Bridge Intel systems and AMD systems appear to cope with this (in so
far as "they seem to work fine"), but Sandy-Bridge systems certainly do not,
resulting in a panic() when the Queued Invalidation wait descriptor is not
executed, and subsequent deadlock because of reentering the kexec_crash()

This behaviour can be fixed by also indicating that interrupt remapping is not
enabled after shutting down the IOMMU.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

This patch is RFC because of several concerns.

* Do we want to turn off more of the IOMMU feature variables as well?  I
  suspect so.

* It looks to me as if this will also cause problems on the S3 path, as
  iommu_disable_x2apic_IR() is called after iommu_shutdown(), yet the
  variables cant change or iommu_resume() will leave things disabled.

diff -r 98f80bf9e286 -r 4247933ebeaa xen/drivers/passthrough/iommu.c
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -601,7 +601,7 @@ void iommu_crash_shutdown(void)
     const struct iommu_ops *ops = iommu_get_ops();
     if ( iommu_enabled )
-    iommu_enabled = 0;
+    iommu_enabled = iommu_intremap = 0;
 int iommu_do_domctl(

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