[PATCH v3 4/6] i386: Mask and report unavailable multi-bit feature values

[Lei Wang]

Some feature words, e.g., feature words in AMX-related CPUID leaf 0x1D and
0x1E are not bit-wise but multiple bits represents one value. Handle this
situation when the values specified are not the same as which are reported
by KVM. The handling includes:

 - The responsibility of masking bits and giving warnings are delegated to
   the feature enabler. A framework is also provided to enable this.
 - To simplify the initialization, a default function is provided if the
   the function is not specified.

The reason why delegating this responsibility rather than just marking
them as zeros when they are not same is because different multi-bit
features may have different logic, which is case by case, for example:

 1. CPUID.0x14_0x1:EBX[15:0]. Even though it's multi-bits field, it's a
    bitmap and each bit represents a separate capability.

 2. CPUID.0x14_0x1:EAX[2:0] represents the number of configurable Address
    Ranges. 3 bits as a whole to represent a integer value. It means the
    maximum capability of HW. If KVM reports M, then M to 0 is legal
    value to configure (because KVM can emulate each value correctly).

 3. CPUID.0x1D_0x1:EAX[31:16] represents palette 1 bytes_per_tile. 16 bits
    as a whole represent an integer value. It's not like case 2 and SW
    needs to configure the same value as reported. Because it's not
    possible for SW to configure to a different value and KVM cannot
    emulate it.

So marking them blindly as zeros is incorrect, and delegating this
responsibility can let each multi-bit feature have its own way to mask bits.

Signed-off-by: Lei Wang <lei4.wang@intel.com>
---
 target/i386/cpu-internal.h |  2 ++
 target/i386/cpu.c          | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/target/i386/cpu-internal.h b/target/i386/cpu-internal.h
index 66b3d66cb4..83c7b53926 100644
--- a/target/i386/cpu-internal.h
+++ b/target/i386/cpu-internal.h
@@ -30,6 +30,8 @@ typedef struct MultiBitFeatureInfo {
     uint64_t mask;
     unsigned high_bit_position;
     unsigned low_bit_position;
+    void (*mark_unavailable_multi_bit)(X86CPU *cpu, FeatureWord w, int index,
+                                       const char *verbose_prefix);
 } MultiBitFeatureInfo;
 
 typedef struct FeatureWordInfo {
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 88aa780566..e638a31d34 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -4377,6 +4377,28 @@ static bool x86_cpu_have_filtered_features(X86CPU *cpu)
     return false;
 }
 
+static void mark_unavailable_multi_bit_default(X86CPU *cpu, FeatureWord w,
+                                               int index,
+                                               const char *verbose_prefix)
+{
+    FeatureWordInfo *f = &feature_word_info[w];
+    g_autofree char *feat_word_str = feature_word_description(f);
+    uint64_t host_feat = x86_cpu_get_supported_feature_word(w, false);
+    MultiBitFeatureInfo mf = f->multi_bit_features[index];
+
+    if ((cpu->env.features[w] & mf.mask) &&
+        ((cpu->env.features[w] ^ host_feat) & mf.mask)) {
+        if (!cpu->force_features) {
+            cpu->env.features[w] &= ~mf.mask;
+        }
+        cpu->filtered_features[w] |= mf.mask;
+        if (verbose_prefix)
+            warn_report("%s: %s.%s [%u:%u]", verbose_prefix, feat_word_str,
+                        mf.feat_name, mf.high_bit_position,
+                        mf.low_bit_position);
+    }
+}
+
 static void mark_unavailable_features(X86CPU *cpu, FeatureWord w, uint64_t 
mask,
                                       const char *verbose_prefix)
 {
@@ -6442,6 +6464,20 @@ static void x86_cpu_filter_features(X86CPU *cpu, bool 
verbose)
             x86_cpu_get_supported_feature_word(w, false);
         uint64_t requested_features = env->features[w];
         uint64_t unavailable_features = requested_features & ~host_feat;
+        FeatureWordInfo f = feature_word_info[w];
+        int i;
+
+        for (i = 0; i < f.num_multi_bit_features; i++) {
+            MultiBitFeatureInfo mf = f.multi_bit_features[i];
+            if (mf.mark_unavailable_multi_bit) {
+                mf.mark_unavailable_multi_bit(cpu, w, i, prefix);
+            } else {
+                mark_unavailable_multi_bit_default(cpu, w, i, prefix);
+            }
+
+            unavailable_features &= ~mf.mask;
+        }
+
         mark_unavailable_features(cpu, w, unavailable_features, prefix);
     }
 
-- 
2.34.1