Re: [PATCH] target/i386: Add more features enumerated by CPUID.7.2.EDX

[Zhao Liu <zhao1.liu@intel.com>]

On Thu, Sep 19, 2024 at 01:10:11PM +0800, Chao Gao wrote:
> Date: Thu, 19 Sep 2024 13:10:11 +0800
> From: Chao Gao <chao.gao@intel.com>
> Subject: [PATCH] target/i386: Add more features enumerated by CPUID.7.2.EDX
> X-Mailer: git-send-email 2.46.1
> 
> Following 5 bits in CPUID.7.2.EDX are supported by KVM. Add their
> supports in QEMU. Each of them indicates certain bits of IA32_SPEC_CTRL
> are supported. Those bits can control CPU speculation behavior which can
> be used to defend against side-channel attacks.
> 
> bit0: intel-psfd
>   if 1, indicates bit 7 of the IA32_SPEC_CTRL MSR is supported. Bit 7 of
>   this MSR disables Fast Store Forwarding Predictor without disabling
>   Speculative Store Bypass
> 
> bit1: ipred-ctrl
>   If 1, indicates bits 3 and 4 of the IA32_SPEC_CTRL MSR are supported.
>   Bit 3 of this MSR enables IPRED_DIS control for CPL3. Bit 4 of this
>   MSR enables IPRED_DIS control for CPL0/1/2
> 
> bit2: rrsba-ctrl
>   If 1, indicates bits 5 and 6 of the IA32_SPEC_CTRL MSR are supported.
>   Bit 5 of this MSR disables RRSBA behavior for CPL3. Bit 6 of this MSR
>   disables RRSBA behavior for CPL0/1/2
> 
> bit3: ddpd-u
>   If 1, indicates bit 8 of the IA32_SPEC_CTRL MSR is supported. Bit 8 of
>   this MSR disables Data Dependent Prefetcher.
> 
> bit4: bhi-ctrl
>   if 1, indicates bit 10 of the IA32_SPEC_CTRL MSR is supported. Bit 10
>   of this MSR enables BHI_DIS_S behavior.
> 
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> ---
>  target/i386/cpu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 85ef7452c0..18ba958f46 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -1148,8 +1148,8 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>      [FEAT_7_2_EDX] = {
>          .type = CPUID_FEATURE_WORD,
>          .feat_names = {
> -            NULL, NULL, NULL, NULL,
> -            NULL, "mcdt-no", NULL, NULL,
> +            "intel-psfd", "ipred-ctrl", "rrsba-ctrl", "ddpd-u",
> +            "bhi-ctrl", "mcdt-no", NULL, NULL,

IIUC, these bits depend on "spec-ctrl", which indicates the presence of
IA32_SPEC_CTRL.

Then I think we'd better add dependencies in feature_dependencies[].

-Zhao

>              NULL, NULL, NULL, NULL,
>              NULL, NULL, NULL, NULL,
>              NULL, NULL, NULL, NULL,
> -- 
> 2.46.1
> 
>