linux-kernel - Re: [PATCH v3 03/27] KVM: VMX: Add support for the secondary VM exit controls

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Message-ID: <10aa42de-a448-40d4-a874-514c9deb56a3@zytor.com>
Date: Mon, 21 Oct 2024 10:03:45 -0700
From: Xin Li <xin@...or.com>
To: Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, seanjc@...gle.com, pbonzini@...hat.com,
        corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        luto@...nel.org, peterz@...radead.org, andrew.cooper3@...rix.com
Subject: Re: [PATCH v3 03/27] KVM: VMX: Add support for the secondary VM exit
 controls

On 10/21/2024 1:28 AM, Chao Gao wrote:
>> +	for (i = 0; i < ARRAY_SIZE(vmcs_entry_exit_triplets); i++) {
>> +		u32 n_ctrl = vmcs_entry_exit_triplets[i].entry_control;
>> +		u32 x_ctrl = vmcs_entry_exit_triplets[i].exit_control;
>> +		u64 x_ctrl_2 = vmcs_entry_exit_triplets[i].exit_2nd_control;
>> +		bool has_n = n_ctrl && ((_vmentry_control & n_ctrl) == n_ctrl);
>> +		bool has_x = x_ctrl && ((_vmexit_control & x_ctrl) == x_ctrl);
>> +		bool has_x_2 = x_ctrl_2 && ((_secondary_vmexit_control & x_ctrl_2) == x_ctrl_2);
>> +
>> +		if (x_ctrl_2) {
>> +			/* Only activate secondary VM exit control bit should be set */
>> +			if ((_vmexit_control & x_ctrl) == VM_EXIT_ACTIVATE_SECONDARY_CONTROLS) {
>> +				if (has_n == has_x_2)
>> +					continue;
>> +			} else {
>> +				/* The feature should not be supported in any control */
>> +				if (!has_n && !has_x && !has_x_2)
>> +					continue;
>> +			}
>> +		} else if (has_n == has_x) {
>> 			continue;
>> +		}
>>
>> -		pr_warn_once("Inconsistent VM-Entry/VM-Exit pair, entry = %x, exit = %x\n",
>> -			     _vmentry_control & n_ctrl, _vmexit_control & x_ctrl);
>> +		pr_warn_once("Inconsistent VM-Entry/VM-Exit triplet, entry = %x, exit = %x, secondary_exit = %llx\n",
>> +			     _vmentry_control & n_ctrl, _vmexit_control & x_ctrl,
>> +			     _secondary_vmexit_control & x_ctrl_2);
>>
>> 		if (error_on_inconsistent_vmcs_config)
>> 			return -EIO;
>>
>> 		_vmentry_control &= ~n_ctrl;
>> 		_vmexit_control &= ~x_ctrl;
> 
> w/ patch 4, VM_EXIT_ACTIVATE_SECONDARY_CONTROLS is cleared if FRED fails in the
> consistent check. this means, all features in the secondary vm-exit controls
> are removed. it is overkill.

Good catch!

> 
> I prefer to maintain a separate table for the secondary VM-exit controls:
> 
>   	struct {
>   		u32 entry_control;
>   		u64 exit2_control;
> 	} const vmcs_entry_exit2_pairs[] = {
> 		{ VM_ENTRY_LOAD_IA32_FRED, SECONDARY_VM_EXIT_SAVE_IA32_FRED |
> 					   SECONDARY_VM_EXIT_LOAD_IA32_FRED},
> 	};
> 
> 	for (i = 0; i < ARRAY_SIZE(vmcs_entry_exit2_pairs); i++) {
> 	...
> 	}

Hmm, I prefer one table, as it's more straight forward.

> 
>> +		_secondary_vmexit_control &= ~x_ctrl_2;
>> 	}
>>
>> 	rdmsrl(MSR_IA32_VMX_BASIC, basic_msr);