linux-kernel - Re: [PATCH v6 25/25] KVM: nVMX: Enable CET support for nested guest

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Date:   Wed, 1 Nov 2023 10:09:42 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dave.hansen@...el.com>,
        <peterz@...radead.org>, <rick.p.edgecombe@...el.com>,
        <john.allen@....com>
Subject: Re: [PATCH v6 25/25] KVM: nVMX: Enable CET support for nested guest

On Thu, Sep 14, 2023 at 02:33:25AM -0400, Yang Weijiang wrote:
>Set up CET MSRs, related VM_ENTRY/EXIT control bits and fixed CR4 setting
>to enable CET for nested VM.
>
>Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
>---
> arch/x86/kvm/vmx/nested.c | 27 +++++++++++++++++++++++++--
> arch/x86/kvm/vmx/vmcs12.c |  6 ++++++
> arch/x86/kvm/vmx/vmcs12.h | 14 +++++++++++++-
> arch/x86/kvm/vmx/vmx.c    |  2 ++
> 4 files changed, 46 insertions(+), 3 deletions(-)
>
>diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>index 78a3be394d00..2c4ff13fddb0 100644
>--- a/arch/x86/kvm/vmx/nested.c
>+++ b/arch/x86/kvm/vmx/nested.c
>@@ -660,6 +660,28 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
> 	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
> 					 MSR_IA32_FLUSH_CMD, MSR_TYPE_W);
> 
>+	/* Pass CET MSRs to nested VM if L0 and L1 are set to pass-through. */
>+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
>+					 MSR_IA32_U_CET, MSR_TYPE_RW);
>+
>+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
>+					 MSR_IA32_S_CET, MSR_TYPE_RW);
>+
>+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
>+					 MSR_IA32_PL0_SSP, MSR_TYPE_RW);
>+
>+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
>+					 MSR_IA32_PL1_SSP, MSR_TYPE_RW);
>+
>+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
>+					 MSR_IA32_PL2_SSP, MSR_TYPE_RW);
>+
>+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
>+					 MSR_IA32_PL3_SSP, MSR_TYPE_RW);
>+
>+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
>+					 MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW);
>+
> 	kvm_vcpu_unmap(vcpu, &vmx->nested.msr_bitmap_map, false);
> 
> 	vmx->nested.force_msr_bitmap_recalc = false;
>@@ -6794,7 +6816,7 @@ static void nested_vmx_setup_exit_ctls(struct vmcs_config *vmcs_conf,
> 		VM_EXIT_HOST_ADDR_SPACE_SIZE |
> #endif
> 		VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT |
>-		VM_EXIT_CLEAR_BNDCFGS;
>+		VM_EXIT_CLEAR_BNDCFGS | VM_EXIT_LOAD_CET_STATE;
> 	msrs->exit_ctls_high |=
> 		VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
> 		VM_EXIT_LOAD_IA32_EFER | VM_EXIT_SAVE_IA32_EFER |
>@@ -6816,7 +6838,8 @@ static void nested_vmx_setup_entry_ctls(struct vmcs_config *vmcs_conf,
> #ifdef CONFIG_X86_64
> 		VM_ENTRY_IA32E_MODE |
> #endif
>-		VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_BNDCFGS;
>+		VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_BNDCFGS |
>+		VM_ENTRY_LOAD_CET_STATE;
> 	msrs->entry_ctls_high |=
> 		(VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR | VM_ENTRY_LOAD_IA32_EFER |
> 		 VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL);
>diff --git a/arch/x86/kvm/vmx/vmcs12.c b/arch/x86/kvm/vmx/vmcs12.c
>index 106a72c923ca..4233b5ca9461 100644
>--- a/arch/x86/kvm/vmx/vmcs12.c
>+++ b/arch/x86/kvm/vmx/vmcs12.c
>@@ -139,6 +139,9 @@ const unsigned short vmcs12_field_offsets[] = {
> 	FIELD(GUEST_PENDING_DBG_EXCEPTIONS, guest_pending_dbg_exceptions),
> 	FIELD(GUEST_SYSENTER_ESP, guest_sysenter_esp),
> 	FIELD(GUEST_SYSENTER_EIP, guest_sysenter_eip),
>+	FIELD(GUEST_S_CET, guest_s_cet),
>+	FIELD(GUEST_SSP, guest_ssp),
>+	FIELD(GUEST_INTR_SSP_TABLE, guest_ssp_tbl),

I think we need to sync guest states, e.g., guest_s_cet/guest_ssp/guest_ssp_tbl,
between vmcs02 and vmcs12 on nested VM entry/exit, probably in
sync_vmcs02_to_vmcs12() and prepare_vmcs12() or "_rare" variants of them.