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Date: Sat, 2 Dec 2023 00:15:19 +0800
From: "Yang, Weijiang" <weijiang.yang@...el.com>
To: Maxim Levitsky <mlevitsk@...hat.com>
CC: <seanjc@...gle.com>, <pbonzini@...hat.com>,
<dave.hansen@...el.com>, <linux-kernel@...r.kernel.org>,
<peterz@...radead.org>, <chao.gao@...el.com>,
<rick.p.edgecombe@...el.com>, <john.allen@....com>,
<kvm@...r.kernel.org>
Subject: Re: [PATCH v7 24/26] KVM: x86: Enable CET virtualization for VMX and
advertise to userspace
On 12/1/2023 1:46 AM, Maxim Levitsky wrote:
[...]
>>
>> +static inline bool cpu_has_vmx_basic_no_hw_errcode(void)
>> +{
>> + return ((u64)vmcs_config.basic_cap << 32) &
>> + VMX_BASIC_NO_HW_ERROR_CODE_CC;
>> +}
> I still think that we should add a comment explaining why this check is needed,
> as I said in the previous review.
OK, I'll add some comments above the function. Thanks!
>> +
>> static inline bool cpu_has_virtual_nmis(void)
>> {
>> return vmcs_config.pin_based_exec_ctrl & PIN_BASED_VIRTUAL_NMIS &&
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index c658f2f230df..a1aae8709939 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -2614,6 +2614,7 @@ static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>> { VM_ENTRY_LOAD_IA32_EFER, VM_EXIT_LOAD_IA32_EFER },
>> { VM_ENTRY_LOAD_BNDCFGS, VM_EXIT_CLEAR_BNDCFGS },
>> { VM_ENTRY_LOAD_IA32_RTIT_CTL, VM_EXIT_CLEAR_IA32_RTIT_CTL },
>> + { VM_ENTRY_LOAD_CET_STATE, VM_EXIT_LOAD_CET_STATE },
>> };
>>
>> memset(vmcs_conf, 0, sizeof(*vmcs_conf));
>> @@ -4935,6 +4936,15 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>
>> vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0); /* 22.2.1 */
>>
>> + if (kvm_cpu_cap_has(X86_FEATURE_SHSTK))
>> + vmcs_writel(GUEST_SSP, 0);
>> + if (kvm_cpu_cap_has(X86_FEATURE_SHSTK) ||
>> + kvm_cpu_cap_has(X86_FEATURE_IBT))
>> + vmcs_writel(GUEST_S_CET, 0);
>> + if (kvm_cpu_cap_has(X86_FEATURE_SHSTK) &&
>> + IS_ENABLED(CONFIG_X86_64))
>> + vmcs_writel(GUEST_INTR_SSP_TABLE, 0);
> Looks reasonable now.
>> +
>> kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
>>
>> vpid_sync_context(vmx->vpid);
>> @@ -6354,6 +6364,12 @@ void dump_vmcs(struct kvm_vcpu *vcpu)
>> if (vmcs_read32(VM_EXIT_MSR_STORE_COUNT) > 0)
>> vmx_dump_msrs("guest autostore", &vmx->msr_autostore.guest);
>>
>> + if (vmentry_ctl & VM_ENTRY_LOAD_CET_STATE) {
>> + pr_err("S_CET = 0x%016lx\n", vmcs_readl(GUEST_S_CET));
>> + pr_err("SSP = 0x%016lx\n", vmcs_readl(GUEST_SSP));
>> + pr_err("INTR SSP TABLE = 0x%016lx\n",
>> + vmcs_readl(GUEST_INTR_SSP_TABLE));
>> + }
>> pr_err("*** Host State ***\n");
>> pr_err("RIP = 0x%016lx RSP = 0x%016lx\n",
>> vmcs_readl(HOST_RIP), vmcs_readl(HOST_RSP));
>> @@ -6431,6 +6447,12 @@ void dump_vmcs(struct kvm_vcpu *vcpu)
>> if (secondary_exec_control & SECONDARY_EXEC_ENABLE_VPID)
>> pr_err("Virtual processor ID = 0x%04x\n",
>> vmcs_read16(VIRTUAL_PROCESSOR_ID));
>> + if (vmexit_ctl & VM_EXIT_LOAD_CET_STATE) {
>> + pr_err("S_CET = 0x%016lx\n", vmcs_readl(HOST_S_CET));
>> + pr_err("SSP = 0x%016lx\n", vmcs_readl(HOST_SSP));
>> + pr_err("INTR SSP TABLE = 0x%016lx\n",
>> + vmcs_readl(HOST_INTR_SSP_TABLE));
>> + }
>> }
>>
>> /*
>> @@ -7964,7 +7986,6 @@ static __init void vmx_set_cpu_caps(void)
>> kvm_cpu_cap_set(X86_FEATURE_UMIP);
>>
>> /* CPUID 0xD.1 */
>> - kvm_caps.supported_xss = 0;
>> if (!cpu_has_vmx_xsaves())
>> kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
>>
>> @@ -7976,6 +7997,12 @@ static __init void vmx_set_cpu_caps(void)
>>
>> if (cpu_has_vmx_waitpkg())
>> kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
>> +
>> + if (!cpu_has_load_cet_ctrl() || !enable_unrestricted_guest ||
>> + !cpu_has_vmx_basic_no_hw_errcode()) {
>> + kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
>> + kvm_cpu_cap_clear(X86_FEATURE_IBT);
>> + }
> My review feedback from previous version still applies here, I don't have an
> idea why this was not addressed....
>
> "I think that here we also need to clear kvm_caps.supported_xss,
> or even better, lets set the CET bits in kvm_caps.supported_xss only
> once CET is fully enabled (both this check and check in __kvm_x86_vendor_init pass)."
Ah, previously I had a helper to check whether CET bits were enabled in kvm_caps.supported_xss,
so need to set the bits earlier before vmx's hardware_setup. I still want to keep the code as-is
in case other features need to check the their related bits set before configure something in
vmx hardware_setup.
> In addition to that I just checked and unless I am mistaken:
>
> vmx_set_cpu_caps() is called from vmx's hardware_setup(), which is called
> from __kvm_x86_vendor_init.
>
> After this call, __kvm_x86_vendor_init does clear kvm_caps.supported_xss,
> but doesn't do this if the above code cleared X86_FEATURE_SHSTK/X86_FEATURE_IBT.
>
Yeah, I checked the history, the similar logic was there until v6, I can pick it up, thanks!
>> }
>>
>> static void vmx_request_immediate_exit(struct kvm_vcpu *vcpu)
>> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
>> index c2130d2c8e24..fb72819fbb41 100644
>> --- a/arch/x86/kvm/vmx/vmx.h
>> +++ b/arch/x86/kvm/vmx/vmx.h
>> @@ -480,7 +480,8 @@ static inline u8 vmx_get_rvi(void)
>> VM_ENTRY_LOAD_IA32_EFER | \
>> VM_ENTRY_LOAD_BNDCFGS | \
>> VM_ENTRY_PT_CONCEAL_PIP | \
>> - VM_ENTRY_LOAD_IA32_RTIT_CTL)
>> + VM_ENTRY_LOAD_IA32_RTIT_CTL | \
>> + VM_ENTRY_LOAD_CET_STATE)
>>
>> #define __KVM_REQUIRED_VMX_VM_EXIT_CONTROLS \
>> (VM_EXIT_SAVE_DEBUG_CONTROLS | \
>> @@ -502,7 +503,8 @@ static inline u8 vmx_get_rvi(void)
>> VM_EXIT_LOAD_IA32_EFER | \
>> VM_EXIT_CLEAR_BNDCFGS | \
>> VM_EXIT_PT_CONCEAL_PIP | \
>> - VM_EXIT_CLEAR_IA32_RTIT_CTL)
>> + VM_EXIT_CLEAR_IA32_RTIT_CTL | \
>> + VM_EXIT_LOAD_CET_STATE)
>>
>> #define KVM_REQUIRED_VMX_PIN_BASED_VM_EXEC_CONTROL \
>> (PIN_BASED_EXT_INTR_MASK | \
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index c6b57ede0f57..2bcf3c7923bf 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -231,7 +231,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
>> | XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>> | XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
>>
>> -#define KVM_SUPPORTED_XSS 0
>> +#define KVM_SUPPORTED_XSS (XFEATURE_MASK_CET_USER | \
>> + XFEATURE_MASK_CET_KERNEL)
>>
>> u64 __read_mostly host_efer;
>> EXPORT_SYMBOL_GPL(host_efer);
>> @@ -9854,6 +9855,15 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>> if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
>> kvm_caps.supported_xss = 0;
>>
>> + if ((kvm_caps.supported_xss & (XFEATURE_MASK_CET_USER |
>> + XFEATURE_MASK_CET_KERNEL)) !=
>> + (XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL)) {
>> + kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
>> + kvm_cpu_cap_clear(X86_FEATURE_IBT);
>> + kvm_caps.supported_xss &= ~XFEATURE_CET_USER;
>> + kvm_caps.supported_xss &= ~XFEATURE_CET_KERNEL;
>> + }
>> +
>> #define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f)
>> cr4_reserved_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_);
>> #undef __kvm_cpu_cap_has
>> @@ -12319,7 +12329,9 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>>
>> static inline bool is_xstate_reset_needed(void)
>> {
>> - return kvm_cpu_cap_has(X86_FEATURE_MPX);
>> + return kvm_cpu_cap_has(X86_FEATURE_MPX) ||
>> + kvm_cpu_cap_has(X86_FEATURE_SHSTK) ||
>> + kvm_cpu_cap_has(X86_FEATURE_IBT);
>> }
>>
>> void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>> @@ -12396,6 +12408,16 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>> XFEATURE_BNDCSR);
>> }
>>
>> + if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
>> + fpstate_clear_xstate_component(fpstate,
>> + XFEATURE_CET_USER);
>> + fpstate_clear_xstate_component(fpstate,
>> + XFEATURE_CET_KERNEL);
>> + } else if (kvm_cpu_cap_has(X86_FEATURE_IBT)) {
>> + fpstate_clear_xstate_component(fpstate,
>> + XFEATURE_CET_USER);
>> + }
>> +
>> if (init_event)
>> kvm_load_guest_fpu(vcpu);
>> }
>> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
>> index d9cc352cf421..dc79dcd733ac 100644
>> --- a/arch/x86/kvm/x86.h
>> +++ b/arch/x86/kvm/x86.h
>> @@ -531,6 +531,9 @@ bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
>> __reserved_bits |= X86_CR4_VMXE; \
>> if (!__cpu_has(__c, X86_FEATURE_PCID)) \
>> __reserved_bits |= X86_CR4_PCIDE; \
>> + if (!__cpu_has(__c, X86_FEATURE_SHSTK) && \
>> + !__cpu_has(__c, X86_FEATURE_IBT)) \
>> + __reserved_bits |= X86_CR4_CET; \
>> __reserved_bits; \
>> })
>>
>
> Best regards,
> Maxim Levitsky
>
>
>
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