linux-kernel - Re: [RFC PATCH v2 04/11] KVM: VMX: Add IA32_SPEC

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Message-ID: <ZD37c+/9l/nbvPnr@chao-env>
Date:   Tue, 18 Apr 2023 10:07:47 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
CC:     <kvm@...r.kernel.org>, Jiaan Lu <jiaan.lu@...el.com>,
        Zhang Chen <chen.zhang@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 04/11] KVM: VMX: Add IA32_SPEC_CTRL virtualization
 support

On Mon, Apr 17, 2023 at 11:17:36AM +0800, Binbin Wu wrote:
>
>On 4/14/2023 2:25 PM, Chao Gao wrote:
>> From: Zhang Chen <chen.zhang@...el.com>
>> 
>> Currently KVM disables interception of IA32_SPEC_CTRL after a non-0 is
>> written to IA32_SPEC_CTRL by guest. Then, guest is allowed to write any
>> value to hardware.
>> 
>> "virtualize IA32_SPEC_CTRL" is a new tertiary vm-exec control. This
>> feature allows KVM to specify that certain bits of the IA32_SPEC_CTRL
>> MSR cannot be modified by guest software.
>> 
>> Two VMCS fields are added:
>> 
>>    IA32_SPEC_CTRL_MASK:   bits that guest software cannot modify
>>    IA32_SPEC_CTRL_SHADOW: value that guest software expects to be in the
>> 			 IA32_SPEC_CTRL MSR
>> 
>> On rdmsr, the shadow value is returned. on wrmsr, EDX:EAX is written
>> to the IA32_SPEC_CTRL_SHADOW and (cur_val & mask) | (EDX:EAX & ~mask)
>> is written to the IA32_SPEC_CTRL MSR, where
>>    * cur_val is the original value of IA32_SPEC_CTRL MSR
>>    * mask is the value of IA32_SPEC_CTRL_MASK
>> 
>> Add a mask e.g.,
>
>e.g. or i.e. ?

Yes, here should be "i.e.".

>> +static inline void vmx_set_guest_spec_ctrl(struct vcpu_vmx *vmx, u64 val)
>> +{
>> +	vmx->guest_spec_ctrl = val;
>> +
>> +	/*
>> +	 * For simplicity, always keep IA32_SPEC_CTRL_SHADOW up-to-date,
>> +	 * regardless of the MSR intercept state.
>
>It is better to use "IA32_SPEC_CTRL"  explicitly instead of "the MSR" to
>avoid misunderstand.

Agreed. Will do.