Re: [PATCH v11 8/9] KVM: VMX: Enable CET support for nested VM

From: Sean Christopherson
Date: Thu Apr 23 2020 - 14:29:09 EST

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On Thu, Mar 26, 2020 at 04:18:45PM +0800, Yang Weijiang wrote:
> CET MSRs pass through guests for performance consideration.
> Configure the MSRs to match L0/L1 settings so that nested VM
> is able to run with CET.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
> arch/x86/kvm/vmx/nested.c | 41 +++++++++++++++++++++++++++++++++++++--
> arch/x86/kvm/vmx/vmcs12.c | 6 ++++++
> arch/x86/kvm/vmx/vmcs12.h | 14 ++++++++++++-
> arch/x86/kvm/vmx/vmx.c | 1 +
> 4 files changed, 59 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index e47eb7c0fbae..a71ef33de55f 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -627,6 +627,41 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
> nested_vmx_disable_intercept_for_msr(msr_bitmap_l1, msr_bitmap_l0,
> MSR_KERNEL_GS_BASE, MSR_TYPE_RW);
>
> + /* Pass CET MSRs to nested VM if L0 and L1 are set to pass-through. */
> + if (!msr_write_intercepted_l01(vcpu, MSR_IA32_U_CET))
> + nested_vmx_disable_intercept_for_msr(
> + msr_bitmap_l1, msr_bitmap_l0,
> + MSR_IA32_U_CET, MSR_TYPE_RW);
> +
> + if (!msr_write_intercepted_l01(vcpu, MSR_IA32_PL3_SSP))
> + nested_vmx_disable_intercept_for_msr(
> + msr_bitmap_l1, msr_bitmap_l0,
> + MSR_IA32_PL3_SSP, MSR_TYPE_RW);
> +
> + if (!msr_write_intercepted_l01(vcpu, MSR_IA32_S_CET))
> + nested_vmx_disable_intercept_for_msr(
> + msr_bitmap_l1, msr_bitmap_l0,
> + MSR_IA32_S_CET, MSR_TYPE_RW);
> +
> + if (!msr_write_intercepted_l01(vcpu, MSR_IA32_PL0_SSP))
> + nested_vmx_disable_intercept_for_msr(
> + msr_bitmap_l1, msr_bitmap_l0,
> + MSR_IA32_PL0_SSP, MSR_TYPE_RW);
> +
> + if (!msr_write_intercepted_l01(vcpu, MSR_IA32_PL1_SSP))
> + nested_vmx_disable_intercept_for_msr(
> + msr_bitmap_l1, msr_bitmap_l0,
> + MSR_IA32_PL1_SSP, MSR_TYPE_RW);
> +
> + if (!msr_write_intercepted_l01(vcpu, MSR_IA32_PL2_SSP))
> + nested_vmx_disable_intercept_for_msr(
> + msr_bitmap_l1, msr_bitmap_l0,
> + MSR_IA32_PL2_SSP, MSR_TYPE_RW);
> +
> + if (!msr_write_intercepted_l01(vcpu, MSR_IA32_INT_SSP_TAB))
> + nested_vmx_disable_intercept_for_msr(
> + msr_bitmap_l1, msr_bitmap_l0,
> + MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW);

That's a lot of copy-paste. Maybe add a helper to do the conditional l01
check and subsequent call to nested_vmx_disable_intercept_for_msr()? It's
still a lot of boilerplate, but it's at least a little better. Not sure
what a good name would be.

nested_vmx_update_intercept_for_msr(vcpu, MSR_IA32_U_CET,
msr_bitmap_l1, msr_bitmap_l0,
MSR_TYPE_RW);

> /*
> * Checking the L0->L1 bitmap is trying to verify two things:
> *
> @@ -6040,7 +6075,8 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
> msrs->exit_ctls_high |=
> VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
> VM_EXIT_LOAD_IA32_EFER | VM_EXIT_SAVE_IA32_EFER |
> - VM_EXIT_SAVE_VMX_PREEMPTION_TIMER | VM_EXIT_ACK_INTR_ON_EXIT;
> + VM_EXIT_SAVE_VMX_PREEMPTION_TIMER | VM_EXIT_ACK_INTR_ON_EXIT |
> + VM_EXIT_LOAD_HOST_CET_STATE;
>
> /* We support free control of debug control saving. */
> msrs->exit_ctls_low &= ~VM_EXIT_SAVE_DEBUG_CONTROLS;
> @@ -6057,7 +6093,8 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
> #endif
> VM_ENTRY_LOAD_IA32_PAT;
> msrs->entry_ctls_high |=
> - (VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR | VM_ENTRY_LOAD_IA32_EFER);
> + (VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR | VM_ENTRY_LOAD_IA32_EFER |
> + VM_ENTRY_LOAD_GUEST_CET_STATE);

This is wrong, the OR path is only for emulated stuff, I'm guessing you're
not planning on emulating CET :-)

And I think this needs to be conditional based on supported_xss?

> /* We support free control of debug control loading. */
> msrs->entry_ctls_low &= ~VM_ENTRY_LOAD_DEBUG_CONTROLS;
> diff --git a/arch/x86/kvm/vmx/vmcs12.c b/arch/x86/kvm/vmx/vmcs12.c
> index 53dfb401316d..82b82bebeee0 100644
> --- a/arch/x86/kvm/vmx/vmcs12.c
> +++ b/arch/x86/kvm/vmx/vmcs12.c
> @@ -141,6 +141,9 @@ const unsigned short vmcs_field_to_offset_table[] = {
> 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),
> FIELD(HOST_CR0, host_cr0),
> FIELD(HOST_CR3, host_cr3),
> FIELD(HOST_CR4, host_cr4),
> @@ -153,5 +156,8 @@ const unsigned short vmcs_field_to_offset_table[] = {
> FIELD(HOST_IA32_SYSENTER_EIP, host_ia32_sysenter_eip),
> FIELD(HOST_RSP, host_rsp),
> FIELD(HOST_RIP, host_rip),
> + FIELD(HOST_S_CET, host_s_cet),
> + FIELD(HOST_SSP, host_ssp),
> + FIELD(HOST_INTR_SSP_TABLE, host_ssp_tbl),
> };
> const unsigned int nr_vmcs12_fields = ARRAY_SIZE(vmcs_field_to_offset_table);
> diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h
> index d0c6df373f67..62b7be68f05c 100644
> --- a/arch/x86/kvm/vmx/vmcs12.h
> +++ b/arch/x86/kvm/vmx/vmcs12.h
> @@ -118,7 +118,13 @@ struct __packed vmcs12 {
> natural_width host_ia32_sysenter_eip;
> natural_width host_rsp;
> natural_width host_rip;
> - natural_width paddingl[8]; /* room for future expansion */
> + natural_width host_s_cet;
> + natural_width host_ssp;
> + natural_width host_ssp_tbl;
> + natural_width guest_s_cet;
> + natural_width guest_ssp;
> + natural_width guest_ssp_tbl;
> + natural_width paddingl[2]; /* room for future expansion */

Tangetial topic, it'd be helpful if FIELD and FIELD64 had compile-time
assertions similar to vmcs_read*() to verify the size of the vmcs12 field
is correct. In other words, I don't feel like reviewing all of these :-).

> u32 pin_based_vm_exec_control;
> u32 cpu_based_vm_exec_control;
> u32 exception_bitmap;
> @@ -301,6 +307,12 @@ static inline void vmx_check_vmcs12_offsets(void)
> CHECK_OFFSET(host_ia32_sysenter_eip, 656);
> CHECK_OFFSET(host_rsp, 664);
> CHECK_OFFSET(host_rip, 672);
> + CHECK_OFFSET(host_s_cet, 680);
> + CHECK_OFFSET(host_ssp, 688);
> + CHECK_OFFSET(host_ssp_tbl, 696);
> + CHECK_OFFSET(guest_s_cet, 704);
> + CHECK_OFFSET(guest_ssp, 712);
> + CHECK_OFFSET(guest_ssp_tbl, 720);
> CHECK_OFFSET(pin_based_vm_exec_control, 744);
> CHECK_OFFSET(cpu_based_vm_exec_control, 748);
> CHECK_OFFSET(exception_bitmap, 752);
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index a3d01014b9e7..c2e950d378bd 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7153,6 +7153,7 @@ static void nested_vmx_cr_fixed1_bits_update(struct kvm_vcpu *vcpu)
> cr4_fixed1_update(X86_CR4_PKE, ecx, feature_bit(PKU));
> cr4_fixed1_update(X86_CR4_UMIP, ecx, feature_bit(UMIP));
> cr4_fixed1_update(X86_CR4_LA57, ecx, feature_bit(LA57));
> + cr4_fixed1_update(X86_CR4_CET, ecx, feature_bit(SHSTK));
>
> #undef cr4_fixed1_update
> }
> --
> 2.17.2
>

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