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

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Message-ID: <ZxYQvmc9Ke+PYGkQ@intel.com>
Date: Mon, 21 Oct 2024 16:28:46 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Xin Li (Intel)" <xin@...or.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

>@@ -2713,21 +2715,43 @@ static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
> 				&_vmentry_control))
> 		return -EIO;
> 
>-	for (i = 0; i < ARRAY_SIZE(vmcs_entry_exit_pairs); i++) {
>-		u32 n_ctrl = vmcs_entry_exit_pairs[i].entry_control;
>-		u32 x_ctrl = vmcs_entry_exit_pairs[i].exit_control;
>-
>-		if (!(_vmentry_control & n_ctrl) == !(_vmexit_control & x_ctrl))
>+	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);
>+
>+	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.

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++) {
	...
	}

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