[PATCH] Revert "intel_iommu: Fix irqchip / X2APIC configuration checks"

[Peter Xu <peterx@redhat.com>]

It's true that when vcpus<=255 we don't require the length of 32bit APIC
IDs.  However here since we already have EIM=ON it means the hypervisor
will declare the VM as x2apic supported (e.g. VT-d ECAP register will have
EIM bit 4 set), so the guest should assume the APIC IDs are 32bits width
even if vcpus<=255.  In short, commit 77250171bdc breaks any simple cmdline
that wants to boot a VM with >=9 but <=255 vcpus with:

  -device intel-iommu,intremap=on

For anyone who does not want to enable x2apic, we can use eim=off in the
intel-iommu parameters to skip enabling KVM x2apic.

This partly reverts commit 77250171bdc02aee106083fd2a068147befa1a38, while
keeping the valid bit on checking split irqchip, but revert the other change.

Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Claudio Fontana <cfontana@suse.de>
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/i386/intel_iommu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 05d53a1aa9..6524c2ee32 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -3818,6 +3818,11 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error **errp)
             error_setg(errp, "eim=on requires accel=kvm,kernel-irqchip=split");
             return false;
         }
+        if (!kvm_enable_x2apic()) {
+            error_setg(errp, "eim=on requires support on the KVM side"
+                             "(X2APIC_API, first shipped in v4.7)");
+            return false;
+        }
     }
 
     /* Currently only address widths supported are 39 and 48 bits */
-- 
2.32.0