On Fri, Jan 06, 2023 at 12:38:24AM -0800, Lei Wang wrote:
> 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.w...@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) &&
With this checking bits are all 0 but covered by mf.mask's range are skippped,
even if they're different from the host_feat, please check whether it's desried
behavior.
> + ((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
>
>
