On Tue, 2024-07-02 at 05:17 +0000, Sandesh Patel wrote: > > The error is due to invalid MSIX routing entry passed to KVM. > > The VM boots fine if we attach a vIOMMU but adding a vIOMMU can > potentially result in IO performance loss in guest. > I was interested to know if someone could boot a large Windows VM by > some other means like kvm-msi-ext-dest-id.
I think I may (with Alex Graf's suggestion) have found the Windows bug
with Intel IOMMU.
It looks like when interrupt remapping is enabled with an AMD CPU,
Windows *assumes* it can generate AMD-style MSI messages even if the
IOMMU is an Intel one. If we put a little hack into the IOMMU interrupt
remapping to make it interpret an AMD-style message, Windows seems to
boot at least a little bit further than it did before...
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -3550,9 +3550,14 @@ static int vtd_interrupt_remap_msi(IntelIOMMUState
*iommu,
/* This is compatible mode. */
if (addr.addr.int_mode != VTD_IR_INT_FORMAT_REMAP) {
- memcpy(translated, origin, sizeof(*origin));
- goto out;
- }
+ if (0) {
+ memcpy(translated, origin, sizeof(*origin));
+ goto out;
+ }
+ /* Pretend it's an AMD-format remappable MSI (Yay Windows!) */
+ index = origin->data & 0x7ff;
+ printf("Compat mode index 0x%x\n", index);
+ } else
index = addr.addr.index_h << 15 | addr.addr.index_l;
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