[PATCH v6 04/11] xen/x86: Add supporting code for uploading LAPIC contexts during domain create

[Alejandro Vallejo <alejandro.vallejo@cloud.com>]

If toolstack were to upload LAPIC contexts as part of domain creation it
would encounter a problem were the architectural state does not reflect
the APIC ID in the hidden state. This patch ensures updates to the
hidden state trigger an update in the architectural registers so the
APIC ID in both is consistent.

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
---
 xen/arch/x86/hvm/vlapic.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 02570f9dd63a..a8183c3023da 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -1640,7 +1640,27 @@ static int cf_check lapic_load_hidden(struct domain *d, hvm_domain_context_t *h)
 
     s->loaded.hw = 1;
     if ( s->loaded.regs )
+    {
+        /*
+         * We already processed architectural regs in lapic_load_regs(), so
+         * this must be a migration. Fix up inconsistencies from any older Xen.
+         */
         lapic_load_fixup(s);
+    }
+    else
+    {
+        /*
+         * We haven't seen architectural regs so this could be a migration or a
+         * plain domain create. In the domain create case it's fine to modify
+         * the architectural state to align it to the APIC ID that was just
+         * uploaded and in the migrate case it doesn't matter because the
+         * architectural state will be replaced by the LAPIC_REGS ctx later on.
+         */
+        if ( vlapic_x2apic_mode(s) )
+            set_x2apic_id(s);
+        else
+            vlapic_set_reg(s, APIC_ID, SET_xAPIC_ID(s->hw.x2apic_id));
+    }
 
     hvm_update_vlapic_mode(v);
 
-- 
2.46.0