Re: [PATCH v3 8/8] x86: vmx: virtualize split lock detection

From: Arvind Sankar
Date: Fri Feb 07 2020 - 13:27:13 EST

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In reply to: Xiaoyao Li: "[PATCH v3 8/8] x86: vmx: virtualize split lock detection"
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On Thu, Feb 06, 2020 at 03:04:12PM +0800, Xiaoyao Li wrote:
> Due to the fact that MSR_TEST_CTRL is per-core scope, i.e., the sibling
> threads in the same physical CPU core share the same MSR, only
> advertising feature split lock detection to guest when SMT is disabled
> or unsupported for simplicitly.
>
> Below summarizing how guest behaves of different host configuration:
>
> sld_fatal - MSR_TEST_CTL.SDL is forced on and is sticky from the guest's
^^^ typo
> perspective (so the guest can detect a forced fatal mode).

Is the part in parentheses actually true currently, before adding [1] Sean's
suggested SPLIT_LOCK_DETECT_STICKY bit? How would the guest detect the
forced fatal mode without that?

[1] https://lore.kernel.org/kvm/20200204060353.GB31665@xxxxxxxxxxxxxxx/

>
> sld_warn - SLD is exposed to the guest. MSR_TEST_CTRL.SLD is left on
> until an #AC is intercepted with MSR_TEST_CTRL.SLD=0 in the
> guest, at which point normal sld_warn rules apply. If a vCPU
> associated with the task does VM-Enter with
> MSR_TEST_CTRL.SLD=1, TIF_SLD is reset and the cycle begins
> anew.
>
> sld_off - When set by the guest, MSR_TEST_CTL.SLD is set on VM-Entry
> and cleared on VM-Exit if guest enables SLD.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> ---
> arch/x86/include/asm/cpu.h | 2 ++
> arch/x86/kernel/cpu/intel.c | 7 +++++
> arch/x86/kvm/vmx/vmx.c | 59 +++++++++++++++++++++++++++++++++++--
> arch/x86/kvm/vmx/vmx.h | 1 +
> arch/x86/kvm/x86.c | 14 +++++++--
> 5 files changed, 79 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index f5172dbd3f01..2920de10e72c 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -46,6 +46,7 @@ unsigned int x86_stepping(unsigned int sig);
> extern void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c);
> extern void switch_to_sld(unsigned long tifn);
> extern bool handle_user_split_lock(unsigned long ip);
> +extern void sld_turn_back_on(void);
> extern bool split_lock_detect_enabled(void);
> extern bool split_lock_detect_fatal(void);
> #else
> @@ -55,6 +56,7 @@ static inline bool handle_user_split_lock(unsigned long ip)
> {
> return false;
> }
> +static inline void sld_turn_back_on(void) {}
> static inline bool split_lock_detect_enabled(void) { return false; }
> static inline bool split_lock_detect_fatal(void) { return false; }
> #endif
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index b67b46ea66df..28dc1141152b 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -1087,6 +1087,13 @@ bool handle_user_split_lock(unsigned long ip)
> }
> EXPORT_SYMBOL_GPL(handle_user_split_lock);
>
> +void sld_turn_back_on(void)
> +{
> + __sld_msr_set(true);
> + clear_tsk_thread_flag(current, TIF_SLD);
> +}
> +EXPORT_SYMBOL_GPL(sld_turn_back_on);
> +
> /*
> * This function is called only when switching between tasks with
> * different split-lock detection modes. It sets the MSR for the
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 822211975e6c..8735bf0f3dfd 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1781,6 +1781,25 @@ static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
> }
> }
>
> +/*
> + * Note: for guest, feature split lock detection can only be enumerated through
> + * MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT bit. The FMS enumeration is invalid.
> + */
> +static inline bool guest_has_feature_split_lock_detect(struct kvm_vcpu *vcpu)
> +{
> + return vcpu->arch.core_capabilities & MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT;
> +}
> +
> +static inline u64 vmx_msr_test_ctrl_valid_bits(struct kvm_vcpu *vcpu)
> +{
> + u64 valid_bits = 0;
> +
> + if (guest_has_feature_split_lock_detect(vcpu))
> + valid_bits |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
> +
> + return valid_bits;
> +}
> +
> /*
> * Reads an msr value (of 'msr_index') into 'pdata'.
> * Returns 0 on success, non-0 otherwise.
> @@ -1793,6 +1812,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> u32 index;
>
> switch (msr_info->index) {
> + case MSR_TEST_CTRL:
> + if (!msr_info->host_initiated &&
> + !guest_has_feature_split_lock_detect(vcpu))
> + return 1;
> + msr_info->data = vmx->msr_test_ctrl;
> + break;
> #ifdef CONFIG_X86_64
> case MSR_FS_BASE:
> msr_info->data = vmcs_readl(GUEST_FS_BASE);
> @@ -1934,6 +1959,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> u32 index;
>
> switch (msr_index) {
> + case MSR_TEST_CTRL:
> + if (!msr_info->host_initiated &&
> + (!guest_has_feature_split_lock_detect(vcpu) ||
> + data & ~vmx_msr_test_ctrl_valid_bits(vcpu)))
> + return 1;
> + vmx->msr_test_ctrl = data;
> + break;
> case MSR_EFER:
> ret = kvm_set_msr_common(vcpu, msr_info);
> break;
> @@ -4230,6 +4262,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>
> vmx->rmode.vm86_active = 0;
> vmx->spec_ctrl = 0;
> + vmx->msr_test_ctrl = 0;
>
> vmx->msr_ia32_umwait_control = 0;
>
> @@ -4563,6 +4596,11 @@ static inline bool guest_cpu_alignment_check_enabled(struct kvm_vcpu *vcpu)
> (kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
> }
>
> +static inline bool guest_cpu_split_lock_detect_enabled(struct vcpu_vmx *vmx)
> +{
> + return vmx->msr_test_ctrl & MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
> +}
> +
> static int handle_exception_nmi(struct kvm_vcpu *vcpu)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -4658,8 +4696,9 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
> break;
> case AC_VECTOR:
> /*
> - * Inject #AC back to guest only when guest enables legacy
> - * alignment check.
> + * Inject #AC back to guest only when guest is expecting it,
> + * i.e., guest enables legacy alignment check or split lock
> + * detection.
> * Otherwise, it must be an unexpected split lock #AC of guest
> * since hardware SPLIT_LOCK_DETECT bit keeps unchanged set
> * when vcpu is running. In this case, treat guest the same as
> @@ -4670,6 +4709,7 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
> * similar as sending SIGBUS.
> */
> if (!split_lock_detect_enabled() ||
> + guest_cpu_split_lock_detect_enabled(vmx) ||
> guest_cpu_alignment_check_enabled(vcpu)) {
> kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
> return 1;
> @@ -6555,6 +6595,16 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
> */
> x86_spec_ctrl_set_guest(vmx->spec_ctrl, 0);
>
> + if (static_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) &&
> + guest_cpu_split_lock_detect_enabled(vmx)) {
> + if (test_thread_flag(TIF_SLD))
> + sld_turn_back_on();
> + else if (!split_lock_detect_enabled())
> + wrmsrl(MSR_TEST_CTRL,
> + this_cpu_read(msr_test_ctrl_cache) |
> + MSR_TEST_CTRL_SPLIT_LOCK_DETECT);
> + }
> +
> /* L1D Flush includes CPU buffer clear to mitigate MDS */
> if (static_branch_unlikely(&vmx_l1d_should_flush))
> vmx_l1d_flush(vcpu);
> @@ -6589,6 +6639,11 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>
> x86_spec_ctrl_restore_host(vmx->spec_ctrl, 0);
>
> + if (static_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) &&
> + guest_cpu_split_lock_detect_enabled(vmx) &&
> + !split_lock_detect_enabled())
> + wrmsrl(MSR_TEST_CTRL, this_cpu_read(msr_test_ctrl_cache));
> +
> /* All fields are clean at this point */
> if (static_branch_unlikely(&enable_evmcs))
> current_evmcs->hv_clean_fields |=
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 7f42cf3dcd70..4cb8075e0b2a 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -222,6 +222,7 @@ struct vcpu_vmx {
> #endif
>
> u64 spec_ctrl;
> + u64 msr_test_ctrl;
> u32 msr_ia32_umwait_control;
>
> u32 secondary_exec_control;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ed16644289a3..a3bb09319526 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1163,7 +1163,7 @@ static const u32 msrs_to_save_all[] = {
> #endif
> MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
> MSR_IA32_FEAT_CTL, MSR_IA32_BNDCFGS, MSR_TSC_AUX,
> - MSR_IA32_SPEC_CTRL,
> + MSR_IA32_SPEC_CTRL, MSR_TEST_CTRL,
> MSR_IA32_RTIT_CTL, MSR_IA32_RTIT_STATUS, MSR_IA32_RTIT_CR3_MATCH,
> MSR_IA32_RTIT_OUTPUT_BASE, MSR_IA32_RTIT_OUTPUT_MASK,
> MSR_IA32_RTIT_ADDR0_A, MSR_IA32_RTIT_ADDR0_B,
> @@ -1345,7 +1345,12 @@ static u64 kvm_get_arch_capabilities(void)
>
> static u64 kvm_get_core_capabilities(void)
> {
> - return 0;
> + u64 data = 0;
> +
> + if (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) && !cpu_smt_possible())
> + data |= MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT;
> +
> + return data;
> }
>
> static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
> @@ -5259,6 +5264,11 @@ static void kvm_init_msr_list(void)
> * to the guests in some cases.
> */
> switch (msrs_to_save_all[i]) {
> + case MSR_TEST_CTRL:
> + if (!(kvm_get_core_capabilities() &
> + MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT))
> + continue;
> + break;
> case MSR_IA32_BNDCFGS:
> if (!kvm_mpx_supported())
> continue;
> --
> 2.23.0
>

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In reply to: Xiaoyao Li: "[PATCH v3 8/8] x86: vmx: virtualize split lock detection"
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