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Date: Fri, 24 Apr 2020 23:24:19 +0800
From: Yang Weijiang <weijiang.yang@...el.com>
To: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: Yang Weijiang <weijiang.yang@...el.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, pbonzini@...hat.com,
jmattson@...gle.com, yu.c.zhang@...ux.intel.com
Subject: Re: [PATCH v11 8/9] KVM: VMX: Enable CET support for nested VM
On Thu, Apr 23, 2020 at 11:29:06AM -0700, Sean Christopherson wrote:
> 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@...el.com>
> > ---
> > 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);
>
OK, I'll figure out how to make it nicer :-)
>
> > /*
> > * 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 :-)
When I tested nested VM, if it's not "ORed" here, nested VM entry will
fail, so what's your suggestion on this?
>
> And I think this needs to be conditional based on supported_xss?
Yes, a check is necessary.
>
> > /* 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 :-).
>
OK, let me figure out how to polish them...
> > 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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