linux-kernel - Re: [PATCH v1 05/23] KVM: VMX: Initialize FRED VM entry/exit controls in vmcs

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Date:   Mon, 13 Nov 2023 19:18:47 +0200
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     Xin Li <xin3.li@...el.com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, corbet@....net,
        kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, vkuznets@...hat.com, peterz@...radead.org,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH v1 05/23] KVM: VMX: Initialize FRED VM entry/exit controls
 in vmcs_config



On 8.11.23 г. 20:29 ч., Xin Li wrote:
> Setup the global vmcs_config for FRED:
> 1) Add VM_ENTRY_LOAD_IA32_FRED to KVM_OPTIONAL_VMX_VM_ENTRY_CONTROLS to
>     have a FRED CPU load guest FRED MSRs from VMCS upon VM entry.
> 2) Add SECONDARY_VM_EXIT_SAVE_IA32_FRED to
>     KVM_OPTIONAL_VMX_SECONDARY_VM_EXIT_CONTROLS to have a FRED CPU save
>     guest FRED MSRs to VMCS during VM exit.
> 3) add SECONDARY_VM_EXIT_LOAD_IA32_FRED to
>     KVM_OPTIONAL_VMX_SECONDARY_VM_EXIT_CONTROLS to have a FRED CPU load
>     host FRED MSRs from VMCS during VM exit.
> 
> Also add sanity checks to make sure FRED VM entry/exit controls can be
> set on a FRED CPU.
> 
> Tested-by: Shan Kang <shan.kang@...el.com>
> Signed-off-by: Xin Li <xin3.li@...el.com>
> ---
>   arch/x86/include/asm/vmx.h |  3 +++
>   arch/x86/kvm/vmx/vmx.c     | 19 ++++++++++++++++++-
>   arch/x86/kvm/vmx/vmx.h     |  7 +++++--
>   3 files changed, 26 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index 4d4177ec802c..41796a733bc9 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -106,6 +106,8 @@
>   #define VM_EXIT_PT_CONCEAL_PIP			0x01000000
>   #define VM_EXIT_CLEAR_IA32_RTIT_CTL		0x02000000
>   #define VM_EXIT_ACTIVATE_SECONDARY_CONTROLS	0x80000000
> +#define SECONDARY_VM_EXIT_SAVE_IA32_FRED	0x00000001
> +#define SECONDARY_VM_EXIT_LOAD_IA32_FRED	0x00000002
>   
>   #define VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR	0x00036dff
>   
> @@ -119,6 +121,7 @@
>   #define VM_ENTRY_LOAD_BNDCFGS                   0x00010000
>   #define VM_ENTRY_PT_CONCEAL_PIP			0x00020000
>   #define VM_ENTRY_LOAD_IA32_RTIT_CTL		0x00040000
> +#define VM_ENTRY_LOAD_IA32_FRED			0x00800000
>   
>   #define VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR	0x000011ff
>   
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index df769207cbe0..9186f41974ab 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2694,10 +2694,27 @@ static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>   		_vmexit_control &= ~x_ctrl;
>   	}
>   
> -	if (_vmexit_control & VM_EXIT_ACTIVATE_SECONDARY_CONTROLS)
> +	if (_vmexit_control & VM_EXIT_ACTIVATE_SECONDARY_CONTROLS) {
>   		_secondary_vmexit_control =
>   			adjust_vmx_controls64(KVM_OPTIONAL_VMX_SECONDARY_VM_EXIT_CONTROLS,
>   					      MSR_IA32_VMX_EXIT_CTLS2);
> +		if (cpu_feature_enabled(X86_FEATURE_FRED) &&
> +		    !(_secondary_vmexit_control & SECONDARY_VM_EXIT_SAVE_IA32_FRED &&
> +		      _secondary_vmexit_control & SECONDARY_VM_EXIT_LOAD_IA32_FRED)) {

Can those checks actually trigger? I.e if FEATURE_FRED is set it means 
the CPU implements the FRED spec. According to the spec it's guaranteed 
that VMX_EXIT_CTLS2 will contain those bits set to 1. So aren't those 
checks superfluous?

> +			pr_warn_once("FRED enabled but no VMX VM-Exit {SAVE,LOAD}_IA32_FRED controls: %llx\n",
> +				     _secondary_vmexit_control);
> +			if (error_on_inconsistent_vmcs_config)
> +				return -EIO;
> +		}
> +	}
> +
> +	if (cpu_feature_enabled(X86_FEATURE_FRED) &&
> +	    !(_vmentry_control & VM_ENTRY_LOAD_IA32_FRED)) {
DITTO

<snip>