[v2,3/8] x86/vlapic: Move lapic_load_hidden migration checks to the check hook

Commit Message

Alejandro Vallejo May 8, 2024, 12:39 p.m. UTC

While at it, add a check for the reserved field in the hidden save area.

Signed-off-by: Alejandro Vallejo <[e-mail]>
---
v2:
  * New patch. Addresses the missing check for rsvd_zero in v1.
---
 xen/arch/x86/hvm/vlapic.c | 41 ++++++++++++++++++++++++++++-----------
 1 file changed, 30 insertions(+), 11 deletions(-)

Patch

diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 8a244100009c..2f06bff1b2cc 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -1573,35 +1573,54 @@  static void lapic_load_fixup(struct vlapic *vlapic)
                v, vlapic->loaded.id, vlapic->loaded.ldr, good_ldr);
 }
 
-static int cf_check lapic_load_hidden(struct domain *d, hvm_domain_context_t *h)
+static int cf_check lapic_check_hidden(const struct domain *d,
+                                       hvm_domain_context_t *h)
 {
     unsigned int vcpuid = hvm_load_instance(h);
-    struct vcpu *v;
-    struct vlapic *s;
+    struct hvm_hw_lapic s;
 
     if ( !has_vlapic(d) )
         return -ENODEV;
 
     /* Which vlapic to load? */
-    if ( vcpuid >= d->max_vcpus || (v = d->vcpu[vcpuid]) == NULL )
+    if ( vcpuid >= d->max_vcpus || d->vcpu[vcpuid] == NULL )
     {
         dprintk(XENLOG_G_ERR, "HVM restore: dom%d has no apic%u\n",
                 d->domain_id, vcpuid);
         return -EINVAL;
     }
-    s = vcpu_vlapic(v);
 
-    if ( hvm_load_entry_zeroextend(LAPIC, h, &s->hw) != 0 )
+    if ( hvm_load_entry_zeroextend(LAPIC, h, &s) )
+        return -ENODATA;
+
+    /* EN=0 with EXTD=1 is illegal */
+    if ( (s.apic_base_msr & (APIC_BASE_ENABLE | APIC_BASE_EXTD)) ==
+         APIC_BASE_EXTD )
+        return -EINVAL;
+
+    /*
+     * Fail migrations from newer versions of Xen where
+     * rsvd_zero is interpreted as something else.
+     */
+    if ( s.rsvd_zero )
         return -EINVAL;
 
+    return 0;
+}
+
+static int cf_check lapic_load_hidden(struct domain *d, hvm_domain_context_t *h)
+{
+    unsigned int vcpuid = hvm_load_instance(h);
+    struct vcpu *v = d->vcpu[vcpuid];
+    struct vlapic *s = vcpu_vlapic(v);
+
+    if ( hvm_load_entry_zeroextend(LAPIC, h, &s->hw) != 0 )
+        BUG();
+
     s->loaded.hw = 1;
     if ( s->loaded.regs )
         lapic_load_fixup(s);
 
-    if ( !(s->hw.apic_base_msr & APIC_BASE_ENABLE) &&
-         unlikely(vlapic_x2apic_mode(s)) )
-        return -EINVAL;
-
     hvm_update_vlapic_mode(v);
 
     return 0;
@@ -1643,7 +1662,7 @@  static int cf_check lapic_load_regs(struct domain *d, hvm_domain_context_t *h)
     return 0;
 }
 
-HVM_REGISTER_SAVE_RESTORE(LAPIC, lapic_save_hidden, NULL,
+HVM_REGISTER_SAVE_RESTORE(LAPIC, lapic_save_hidden, lapic_check_hidden,
                           lapic_load_hidden, 1, HVMSR_PER_VCPU);
 HVM_REGISTER_SAVE_RESTORE(LAPIC_REGS, lapic_save_regs, NULL,
                           lapic_load_regs, 1, HVMSR_PER_VCPU);