On Fri, Dec 27, 2019 at 10:11:29AM +0800, Yang Weijiang wrote:
> CET MSRs pass through Guest directly to enhance performance.
> CET runtime control settings are stored in MSR_IA32_{U,S}_CET,
> Shadow Stack Pointer(SSP) are stored in MSR_IA32_PL{0,1,2,3}_SSP,
> SSP table base address is stored in MSR_IA32_INT_SSP_TAB,
> these MSRs are defined in kernel and re-used here.
>
> MSR_IA32_U_CET and MSR_IA32_PL3_SSP are used for user mode protection,
> the contents could differ from process to process, therefore,
> kernel needs to save/restore them during context switch, it makes
> sense to pass through them so that the guest kernel can
> use xsaves/xrstors to operate them efficiently. Other MSRs are used
> for non-user mode protection. See CET spec for detailed info.
>
> The difference between CET VMCS state fields and xsave components is that,
> the former used for CET state storage during VMEnter/VMExit,
> whereas the latter used for state retention between Guest task/process
> switch.
>
> Co-developed-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
> arch/x86/kvm/cpuid.h | 2 ++
> arch/x86/kvm/vmx/vmx.c | 48 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 50 insertions(+)
>
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index d78a61408243..1d77b880084d 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -27,6 +27,8 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
>
> int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu);
>
> +u64 kvm_supported_xss(void);
> +
> static inline int cpuid_maxphyaddr(struct kvm_vcpu *vcpu)
> {
> return vcpu->arch.maxphyaddr;
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 477173e4a85d..61fc846c7ef3 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7091,6 +7091,52 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
> vmx->pt_desc.ctl_bitmask &= ~(0xfULL << (32 + i * 4));
> }
>
> +static void vmx_update_intercept_for_cet_msr(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> + unsigned long *msr_bitmap = vmx->vmcs01.msr_bitmap;
> +
> + /*
> + * U_CET is required for USER CET, per CET spec., meanwhile U_CET and
> + * PL3_SPP are a bundle for USER CET xsaves.
> + */
> + if ((kvm_supported_xss() & XFEATURE_MASK_CET_USER) &&
> + (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
> + guest_cpuid_has(vcpu, X86_FEATURE_IBT))) {
> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW);
> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW);
> + } else {
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW, true);
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW, true);
> + }
I prefer the style of pt_update_intercept_for_msr(), e.g.
flag = (kvm_supported_xss() & XFEATURE_MASK_CET_USER) &&
(guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
guest_cpuid_has(vcpu, X86_FEATURE_IBT));
vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW, flag);
vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW, flag);
flag = (kvm_supported_xss() & XFEATURE_MASK_CET_KERNEL) &&
(guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
guest_cpuid_has(vcpu, X86_FEATURE_IBT));
vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW, flag);
vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW, flag);
vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL1_SSP, MSR_TYPE_RW, flag);
vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_SSP, MSR_TYPE_RW, flag);
/* SSP_TAB only available for KERNEL SHSTK.*/
flag &= guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);
vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW, flag);
> + /*
> + * S_CET is required for KERNEL CET, meanwhile PL0_SSP ... PL2_SSP are a bundle
> + * for CET KERNEL xsaves.
> + */
> + if ((kvm_supported_xss() & XFEATURE_MASK_CET_KERNEL) &&
> + (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
> + guest_cpuid_has(vcpu, X86_FEATURE_IBT))) {
> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW);
> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW);
> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL1_SSP, MSR_TYPE_RW);
> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_SSP, MSR_TYPE_RW);
> +
> + /* SSP_TAB only available for KERNEL SHSTK.*/
> + if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB,
> + MSR_TYPE_RW);
> + else
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB,
> + MSR_TYPE_RW, true);
> + } else {
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW, true);
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW, true);
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL1_SSP, MSR_TYPE_RW, true);
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_SSP, MSR_TYPE_RW, true);
> + vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW, true);
> + }
> +}
> +
> static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -7115,6 +7161,8 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
> guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT))
> update_intel_pt_cfg(vcpu);
> +
> + vmx_update_intercept_for_cet_msr(vcpu);
> }
>
> static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
> --
> 2.17.2
>
