Re: [PATCH v1 3/3] target/i386: Raise the highest index value used for any VMCS encoding

[Zhao Liu]

On Fri, Aug 09, 2024 at 12:38:02AM -0700, Xin Li wrote:
> Date: Fri, 9 Aug 2024 00:38:02 -0700
> From: Xin Li <xin@zytor.com>
> Subject: Re: [PATCH v1 3/3] target/i386: Raise the highest index value used
>  for any VMCS encoding
> 
> On 8/8/2024 11:27 PM, Xin Li wrote:
> > > > +    if (f[FEAT_7_1_EAX] & CPUID_7_1_EAX_FRED) {
> > > > +        /* FRED injected-event data (0x2052).  */
> > > > +        kvm_msr_entry_add(cpu, MSR_IA32_VMX_VMCS_ENUM, 0x52);
> > > 
> > > HMM, I have the questions when I check the FRED spec.
> > > 
> > > Section 9.3.4 said, (for injected-event data) "This field has uses the
> > > encoding pair 2052H/2053H."
> > > 
> > > So why adjust the highest index to 0x52 other than 0x53?
> 
> Okay, found it in the Intel SDM:
> 
> Index. Bits 9:1 distinguish components with the same field width and type.
> 
> Bit 0 is not included in the index field.

Thanks for your education and explanation! I see, for
IA32_VMX_VMCS_ENUM, bit 0 is reserved and only index field is enough.

Regards,
Zhao