[Xen-devel] [PATCH v5 2/4] x86/HVM: fix ID handling of x2APIC emulation

["Jan Beulich" <JBeulich@xxxxxxxx>]

- properly change ID when switching into x2APIC mode (instead of
  mimicking necessary behavior in hvm_x2apic_msr_read())
- correctly (meaningfully) set LDR (so far it ended up being 1 on all
  vCPU-s)
- even if we don't support more than 128 vCPU-s in a HVM guest for now,
  we should properly handle IDs as 32-bit values (i.e. not ignore the
  top 24 bits)
- with that, properly do cluster ID and bit mask check in
  vlapic_match_logical_addr()

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v5: Convert optional checks done in lapic_load_fixup() to trigger a
    printk() instead of preventing the fixup. Move unrelated type
    changes to 3rd patch.
v4: Replace unpause-based approach with one latching most recently
    loaded values.
v2: Some changes broken out to separate patch. Correct ID and
    LDR after domain restore (if necessary); as stated previously the
    only compatibility problem this creates is when migrating a VM _to_
    an unfixed (i.e. old) hypervisor, a scenario which supposedly isn't
    supported.

--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -173,18 +173,17 @@ uint32_t vlapic_set_ppr(struct vlapic *v
    return ppr;
 }
 
-static int vlapic_match_logical_addr(struct vlapic *vlapic, uint8_t mda)
+static int vlapic_match_logical_addr(struct vlapic *vlapic, uint32_t mda)
 {
     int result = 0;
-    uint32_t logical_id;
+    uint32_t logical_id = vlapic_get_reg(vlapic, APIC_LDR);
 
     if ( vlapic_x2apic_mode(vlapic) )
-    {
-        logical_id = vlapic_get_reg(vlapic, APIC_LDR);
-        return !!(logical_id & mda);
-    }
+        return ((logical_id >> 16) == (mda >> 16)) &&
+               (uint16_t)(logical_id & mda);
 
-    logical_id = GET_xAPIC_LOGICAL_ID(vlapic_get_reg(vlapic, APIC_LDR));
+    logical_id = GET_xAPIC_LOGICAL_ID(logical_id);
+    mda = (uint8_t)mda;
 
     switch ( vlapic_get_reg(vlapic, APIC_DFR) )
     {
@@ -208,7 +207,7 @@ static int vlapic_match_logical_addr(str
 
 bool_t vlapic_match_dest(
     struct vlapic *target, struct vlapic *source,
-    int short_hand, uint8_t dest, uint8_t dest_mode)
+    int short_hand, uint32_t dest, uint8_t dest_mode)
 {
     HVM_DBG_LOG(DBG_LEVEL_VLAPIC, "target %p, source %p, dest %#x, "
                 "dest_mode %#x, short_hand %#x",
@@ -219,7 +218,8 @@ bool_t vlapic_match_dest(
     case APIC_DEST_NOSHORT:
         if ( dest_mode )
             return vlapic_match_logical_addr(target, dest);
-        return ((dest == 0xFF) || (dest == VLAPIC_ID(target)));
+        return (dest == _VLAPIC_ID(target, 0xffffffff)) ||
+               (dest == VLAPIC_ID(target));
 
     case APIC_DEST_SELF:
         return (target == source);
@@ -353,7 +353,7 @@ static void vlapic_accept_irq(struct vcp
 
 struct vlapic *vlapic_lowest_prio(
     struct domain *d, struct vlapic *source,
-    int short_hand, uint8_t dest, uint8_t dest_mode)
+    int short_hand, uint32_t dest, uint8_t dest_mode)
 {
     int old = d->arch.hvm_domain.irq.round_robin_prev_vcpu;
     uint32_t ppr, target_ppr = UINT_MAX;
@@ -438,9 +438,7 @@ void vlapic_ipi(
 
     HVM_DBG_LOG(DBG_LEVEL_VLAPIC, "icr = 0x%08x:%08x", icr_high, icr_low);
 
-    dest = (vlapic_x2apic_mode(vlapic)
-            ? icr_high
-            : GET_xAPIC_DEST_FIELD(icr_high));
+    dest = _VLAPIC_ID(vlapic, icr_high);
 
     switch ( icr_low & APIC_MODE_MASK )
     {
@@ -619,10 +617,6 @@ int hvm_x2apic_msr_read(struct vcpu *v, 
     vlapic_read_aligned(vlapic, offset, &low);
     switch ( offset )
     {
-    case APIC_ID:
-        low = GET_xAPIC_ID(low);
-        break;
-
     case APIC_ICR:
         vlapic_read_aligned(vlapic, APIC_ICR2, &high);
         break;
@@ -656,6 +650,8 @@ static int vlapic_reg_write(struct vcpu 
     struct vlapic *vlapic = vcpu_vlapic(v);
     int rc = X86EMUL_OKAY;
 
+    memset(&vlapic->loaded, 0, sizeof(vlapic->loaded));
+
     switch ( offset )
     {
     case APIC_ID:
@@ -960,6 +956,15 @@ const struct hvm_mmio_handler vlapic_mmi
     .write_handler = vlapic_write
 };
 
+static void set_x2apic_id(struct vlapic *vlapic)
+{
+    u32 id = vlapic_vcpu(vlapic)->vcpu_id;
+    u32 ldr = ((id & ~0xf) << 12) | (1 << (id & 0xf));
+
+    vlapic_set_reg(vlapic, APIC_ID, id * 2);
+    vlapic_set_reg(vlapic, APIC_LDR, ldr);
+}
+
 bool_t vlapic_msr_set(struct vlapic *vlapic, uint64_t value)
 {
     if ( (vlapic->hw.apic_base_msr ^ value) & MSR_IA32_APICBASE_ENABLE )
@@ -985,13 +990,10 @@ bool_t vlapic_msr_set(struct vlapic *vla
         return 0;
 
     vlapic->hw.apic_base_msr = value;
+    memset(&vlapic->loaded, 0, sizeof(vlapic->loaded));
 
     if ( vlapic_x2apic_mode(vlapic) )
-    {
-        u32 id = vlapic_get_reg(vlapic, APIC_ID);
-        u32 ldr = ((id & ~0xf) << 16) | (1 << (id & 0xf));
-        vlapic_set_reg(vlapic, APIC_LDR, ldr);
-    }
+        set_x2apic_id(vlapic);
 
     vmx_vlapic_msr_changed(vlapic_vcpu(vlapic));
 
@@ -1263,6 +1265,35 @@ static int lapic_save_regs(struct domain
     return rc;
 }
 
+/*
+ * Following lapic_load_hidden()/lapic_load_regs() we may need to
+ * correct ID and LDR when they come from an old, broken hypervisor.
+ */
+static void lapic_load_fixup(struct vlapic *vlapic)
+{
+    uint32_t id = vlapic->loaded.id;
+
+    if ( vlapic_x2apic_mode(vlapic) && id && vlapic->loaded.ldr == 1 )
+    {
+        /*
+         * This is optional: ID != 0 contradicts LDR == 1. It's being added
+         * to aid in eventual debugging of issues arising from the fixup done
+         * here, but can be dropped as soon as it is found to conflict with
+         * other (future) changes.
+         */
+        if ( GET_xAPIC_ID(id) != vlapic_vcpu(vlapic)->vcpu_id * 2 ||
+             id != SET_xAPIC_ID(GET_xAPIC_ID(id)) )
+            printk(XENLOG_G_WARNING "%pv: bogus APIC ID %#x loaded\n",
+                   vlapic_vcpu(vlapic), id);
+        set_x2apic_id(vlapic);
+    }
+    else /* Undo an eventual earlier fixup. */
+    {
+        vlapic_set_reg(vlapic, APIC_ID, id);
+        vlapic_set_reg(vlapic, APIC_LDR, vlapic->loaded.ldr);
+    }
+}
+
 static int lapic_load_hidden(struct domain *d, hvm_domain_context_t *h)
 {
     uint16_t vcpuid;
@@ -1282,6 +1313,10 @@ static int lapic_load_hidden(struct doma
     if ( hvm_load_entry_zeroextend(LAPIC, h, &s->hw) != 0 ) 
         return -EINVAL;
 
+    s->loaded.hw = 1;
+    if ( s->loaded.regs )
+        lapic_load_fixup(s);
+
     if ( !(s->hw.apic_base_msr & MSR_IA32_APICBASE_ENABLE) &&
          unlikely(vlapic_x2apic_mode(s)) )
         return -EINVAL;
@@ -1310,6 +1345,12 @@ static int lapic_load_regs(struct domain
     if ( hvm_load_entry(LAPIC_REGS, h, s->regs) != 0 ) 
         return -EINVAL;
 
+    s->loaded.id = vlapic_get_reg(s, APIC_ID);
+    s->loaded.ldr = vlapic_get_reg(s, APIC_LDR);
+    s->loaded.regs = 1;
+    if ( s->loaded.hw )
+        lapic_load_fixup(s);
+
     if ( hvm_funcs.process_isr )
         hvm_funcs.process_isr(vlapic_find_highest_isr(s), v);
 
--- a/xen/include/asm-x86/hvm/vlapic.h
+++ b/xen/include/asm-x86/hvm/vlapic.h
@@ -30,8 +30,9 @@
 #define vlapic_vcpu(x)   (container_of((x), struct vcpu, arch.hvm_vcpu.vlapic))
 #define vlapic_domain(x) (vlapic_vcpu(x)->domain)
 
-#define VLAPIC_ID(vlapic)   \
-    (GET_xAPIC_ID(vlapic_get_reg((vlapic), APIC_ID)))
+#define _VLAPIC_ID(vlapic, id) (vlapic_x2apic_mode(vlapic) \
+                                ? (id) : GET_xAPIC_ID(id))
+#define VLAPIC_ID(vlapic) _VLAPIC_ID(vlapic, vlapic_get_reg(vlapic, APIC_ID))
 
 /*
  * APIC can be disabled in two ways:
@@ -70,6 +71,10 @@
 struct vlapic {
     struct hvm_hw_lapic      hw;
     struct hvm_hw_lapic_regs *regs;
+    struct {
+        bool_t               hw, regs;
+        uint32_t             id, ldr;
+    }                        loaded;
     struct periodic_time     pt;
     s_time_t                 timer_last_update;
     struct page_info         *regs_page;
@@ -124,10 +129,10 @@ int vlapic_apicv_write(struct vcpu *v, u
 
 struct vlapic *vlapic_lowest_prio(
     struct domain *d, struct vlapic *source,
-    int short_hand, uint8_t dest, uint8_t dest_mode);
+    int short_hand, uint32_t dest, uint8_t dest_mode);
 
 bool_t vlapic_match_dest(
     struct vlapic *target, struct vlapic *source,
-    int short_hand, uint8_t dest, uint8_t dest_mode);
+    int short_hand, uint32_t dest, uint8_t dest_mode);
 
 #endif /* __ASM_X86_HVM_VLAPIC_H__ */

Attachment: x86-HVM-x2APIC-id.patch
Description: Text document

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