[v4,05/10] xen/x86: Add supporting code for uploading LAPIC contexts during domain create

Commit Message

Alejandro Vallejo June 26, 2024, 4:28 p.m. UTC

This patch is a precondition for a later patch in which toolstack uses HVM
contexts to upload LAPIC data to a newly constructed domain.

If toolstack were to upload LAPIC contexts as part of domain creation as-is 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]>
---
v4:
    * New patch
---
 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 b57e39d1c6dd..ebcf74711a13 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -1622,7 +1622,27 @@  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);