[v5,04/10] xen/x86: Add supporting code for uploading LAPIC contexts during domain create

Commit Message

Alejandro Vallejo Aug. 8, 2024, 1:42 p.m. UTC

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 <[e-mail]>
---
We could also let toolstack synthesise architectural registers, but
that would be adding logic on how architectural state operates to
software that really shouldn't care. I could be persuaded to do it the
other way, but I think it's going to be messier.

v5:
  * No change
---
 xen/arch/x86/hvm/vlapic.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

Patch

diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 0e0699fc8279..3fa839087fe0 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -1620,7 +1620,27 @@  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);