[PATCH] x86/cpu-policy: Extend the guest max policy max leaf/subleaves

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

We already have one migration case opencoded (feat.max_subleaf).  A more
recent discovery is that we advertise x2APIC to guests without ensuring that
we provide max_leaf >= 0xb.

In general, any leaf known to Xen can be safely configured by the toolstack if
it doesn't violate other constraints.

Therefore, introduce guest_common_{max,default}_leaves() to generalise the
special case we currently have for feat.max_subleaf, in preparation to be able
to provide x2APIC topology in leaf 0xb even on older hardware.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>

On a KabyLake I have to hand, here's the delta in what xen-cpuid -p reports:

  git diff --no-index xen-cpuid-p-{before,after}.log
  diff --git a/xen-cpuid-p-before.log b/xen-cpuid-p-after.log
  index 5a76d05..24e22be 100644
  --- a/xen-cpuid-p-before.log
  +++ b/xen-cpuid-p-after.log
  @@ -61,7 +61,7 @@ Host policy: 33 leaves, 2 MSRs
     index    -> value
     000000ce -> 0000000080000000
     0000010a -> 000000000e000c04
  -PV Max policy: 33 leaves, 2 MSRs
  +PV Max policy: 58 leaves, 2 MSRs
    CPUID:
     leaf     subleaf  -> eax      ebx      ecx      edx
     00000000:ffffffff -> 0000000d:756e6547:6c65746e:49656e69
  @@ -75,7 +75,7 @@ PV Max policy: 33 leaves, 2 MSRs
     0000000d:00000000 -> 00000007:00000000:00000340:00000000
     0000000d:00000001 -> 00000007:00000000:00000000:00000000
     0000000d:00000002 -> 00000100:00000240:00000000:00000000
  -  80000000:ffffffff -> 80000008:00000000:00000000:00000000
  +  80000000:ffffffff -> 80000021:00000000:00000000:00000000
     80000001:ffffffff -> 00000000:00000000:00000123:28100800
     80000002:ffffffff -> 65746e49:2952286c:6f655820:2952286e
     80000003:ffffffff -> 55504320:2d334520:30333231:20367620
  @@ -87,7 +87,7 @@ PV Max policy: 33 leaves, 2 MSRs
     index    -> value
     000000ce -> 0000000080000000
     0000010a -> 000000001c020004
  -HVM Max policy: 35 leaves, 2 MSRs
  +HVM Max policy: 60 leaves, 2 MSRs
    CPUID:
     leaf     subleaf  -> eax      ebx      ecx      edx
     00000000:ffffffff -> 0000000d:756e6547:6c65746e:49656e69
  @@ -103,7 +103,7 @@ HVM Max policy: 35 leaves, 2 MSRs
     0000000d:00000002 -> 00000100:00000240:00000000:00000000
     0000000d:00000003 -> 00000040:000003c0:00000000:00000000
     0000000d:00000004 -> 00000040:00000400:00000000:00000000
  -  80000000:ffffffff -> 80000008:00000000:00000000:00000000
  +  80000000:ffffffff -> 80000021:00000000:00000000:00000000
     80000001:ffffffff -> 00000000:00000000:00000123:2c100800
     80000002:ffffffff -> 65746e49:2952286c:6f655820:2952286e
     80000003:ffffffff -> 55504320:2d334520:30333231:20367620
---
 xen/arch/x86/cpu-policy.c | 39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c
index b6d9fad56773..78bc9872b09a 100644
--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -391,6 +391,27 @@ static void __init calculate_host_policy(void)
     p->platform_info.cpuid_faulting = cpu_has_cpuid_faulting;
 }
 
+/*
+ * Guest max policies can have any max leaf/subleaf within bounds.
+ *
+ * - Some incoming VMs have a larger-than-necessary feat max_subleaf.
+ * - Some VMs we'd like to synthesise leaves not present on the host.
+ */
+static void __init guest_common_max_leaves(struct cpu_policy *p)
+{
+    p->basic.max_leaf       = ARRAY_SIZE(p->basic.raw) - 1;
+    p->feat.max_subleaf     = ARRAY_SIZE(p->feat.raw) - 1;
+    p->extd.max_leaf        = 0x80000000U + ARRAY_SIZE(p->extd.raw) - 1;
+}
+
+/* Guest default policies inherit the host max leaf/subleaf settings. */
+static void __init guest_common_default_leaves(struct cpu_policy *p)
+{
+    p->basic.max_leaf       = host_cpu_policy.basic.max_leaf;
+    p->feat.max_subleaf     = host_cpu_policy.feat.max_subleaf;
+    p->extd.max_leaf        = host_cpu_policy.extd.max_leaf;
+}
+
 static void __init guest_common_max_feature_adjustments(uint32_t *fs)
 {
     if ( boot_cpu_data.x86_vendor == X86_VENDOR_INTEL )
@@ -579,11 +600,7 @@ static void __init calculate_pv_max_policy(void)
 
     *p = host_cpu_policy;
 
-    /*
-     * Some VMs may have a larger-than-necessary feat max_subleaf.  Allow them
-     * to migrate in.
-     */
-    p->feat.max_subleaf = ARRAY_SIZE(p->feat.raw) - 1;
+    guest_common_max_leaves(p);
 
     x86_cpu_policy_to_featureset(p, fs);
 
@@ -626,8 +643,7 @@ static void __init calculate_pv_def_policy(void)
 
     *p = pv_max_cpu_policy;
 
-    /* Default to the same max_subleaf as the host. */
-    p->feat.max_subleaf = host_cpu_policy.feat.max_subleaf;
+    guest_common_default_leaves(p);
 
     x86_cpu_policy_to_featureset(p, fs);
 
@@ -666,11 +682,7 @@ static void __init calculate_hvm_max_policy(void)
 
     *p = host_cpu_policy;
 
-    /*
-     * Some VMs may have a larger-than-necessary feat max_subleaf.  Allow them
-     * to migrate in.
-     */
-    p->feat.max_subleaf = ARRAY_SIZE(p->feat.raw) - 1;
+    guest_common_max_leaves(p);
 
     x86_cpu_policy_to_featureset(p, fs);
 
@@ -790,8 +802,7 @@ static void __init calculate_hvm_def_policy(void)
 
     *p = hvm_max_cpu_policy;
 
-    /* Default to the same max_subleaf as the host. */
-    p->feat.max_subleaf = host_cpu_policy.feat.max_subleaf;
+    guest_common_default_leaves(p);
 
     x86_cpu_policy_to_featureset(p, fs);
 

base-commit: 56bd76925ec35085528d778e46123b9d10a66018
-- 
2.39.5