Re: [PATCH v4 16/17] kvm: x86: Add support IA32_CORE_CAPABILITY MSR

[Paolo Bonzini]

On 02/03/19 03:45, Fenghua Yu wrote:
> From: Xiaoyao Li <xiaoyao.li@xxxxxxxxxxxxxxx>
> 
> MSR IA32_CORE_CAPABILITY is a feature-enumerating MSR, bit 5 of which
> reports the capability of enabling detection of split locks (will be
> supported on future processors based on Tremont microarchitecture and
> later).
> 
> Please check the latest Intel Architecture Instruction Set Extensions
> and Future Features Programming Reference for more detailed information
> on the MSR and the split lock bit.
> 
> 1. Expose it to user space as a feature-enumerating MSR, so that user
> space can query it.
> 
> 2. Emualte MSR_IA32_CORE_CAPABILITY with vmx->core_capability. And add the
> get and set handler of MSR_IA32_CORE_CAPABILITY.
>    For uesrspace, it can set this MSR when customizing features of guest,
> also it can read the value of this MSR of guest.
>    For guest, as it's a feature-enumerating MSR, guest only can read it.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxxxxxxxx>
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h |  1 +
>  arch/x86/kvm/vmx/vmx.c          | 23 +++++++++++++++++++++++
>  arch/x86/kvm/vmx/vmx.h          |  1 +
>  arch/x86/kvm/x86.c              | 17 ++++++++++++++++-
>  4 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 180373360e34..208f15570d17 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1527,6 +1527,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
>  		    unsigned long icr, int op_64_bit);
>  
>  u64 kvm_get_arch_capabilities(void);
> +u64 kvm_get_core_capability(void);
>  void kvm_define_shared_msr(unsigned index, u32 msr);
>  int kvm_set_shared_msr(unsigned index, u64 val, u64 mask);
>  
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 30a6bcd735ec..3e03c6e1e558 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1679,6 +1679,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  
>  		msr_info->data = to_vmx(vcpu)->spec_ctrl;
>  		break;
> +	case MSR_IA32_CORE_CAPABILITY:
> +		if (!msr_info->host_initiated &&
> +		    !guest_cpuid_has(vcpu, X86_FEATURE_CORE_CAPABILITY))
> +			return 1;
> +		msr_info->data = vmx->core_capability;
> +		break;
>  	case MSR_IA32_ARCH_CAPABILITIES:
>  		if (!msr_info->host_initiated &&
>  		    !guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES))
> @@ -1891,6 +1897,21 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		vmx_disable_intercept_for_msr(vmx->vmcs01.msr_bitmap, MSR_IA32_PRED_CMD,
>  					      MSR_TYPE_W);
>  		break;
> +	case MSR_IA32_CORE_CAPABILITY:
> +		if (!msr_info->host_initiated)
> +			return 1;
> +		if (data & ~CORE_CAP_SPLIT_LOCK_DETECT)
> +			return 1;
> +
> +		/*
> +		 * Since AC split lock is a hardware feature, and there is no
> +		 * software emulation yet, we cannot enable it for guest if
> +		 * host hardware doesn't support it.
> +		 */
> +		if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
> +			data &= ~CORE_CAP_SPLIT_LOCK_DETECT;
> +		vmx->core_capability = data;
> +		break;
>  	case MSR_IA32_ARCH_CAPABILITIES:
>  		if (!msr_info->host_initiated)
>  			return 1;
> @@ -4083,6 +4104,8 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
>  		++vmx->nmsrs;
>  	}
>  
> +	vmx->core_capability = kvm_get_core_capability();
> +
>  	vmx->arch_capabilities = kvm_get_arch_capabilities();
>  
>  	vm_exit_controls_init(vmx, vmx_vmexit_ctrl());
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 0ac0a64c7790..cc22379991f3 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -191,6 +191,7 @@ struct vcpu_vmx {
>  	u64		      msr_guest_kernel_gs_base;
>  #endif
>  
> +	u64		      core_capability;
>  	u64		      arch_capabilities;
>  	u64		      spec_ctrl;
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 941f932373d0..c3c9e3f2d08a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1125,7 +1125,8 @@ static u32 msrs_to_save[] = {
>  #endif
>  	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
>  	MSR_IA32_FEATURE_CONTROL, MSR_IA32_BNDCFGS, MSR_TSC_AUX,
> -	MSR_IA32_SPEC_CTRL, MSR_IA32_ARCH_CAPABILITIES,
> +	MSR_IA32_SPEC_CTRL, MSR_IA32_CORE_CAPABILITY,
> +	MSR_IA32_ARCH_CAPABILITIES,
>  	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,
> @@ -1197,11 +1198,22 @@ static u32 msr_based_features[] = {
>  
>  	MSR_F10H_DECFG,
>  	MSR_IA32_UCODE_REV,
> +	MSR_IA32_CORE_CAPABILITY,
>  	MSR_IA32_ARCH_CAPABILITIES,
>  };
>  
>  static unsigned int num_msr_based_features;
>  
> +u64 kvm_get_core_capability(void)
> +{
> +	u64 data;
> +
> +	rdmsrl_safe(MSR_IA32_CORE_CAPABILITY, &data);

This patch should be merged with the previous patch.  Also here you
should add:

	data &= CORE_CAP_SPLIT_LOCK_DETECT;

so that non-virtualizable features are hidden and

	if (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
		data |= CORE_CAP_SPLIT_LOCK_DETECT;

so that userspace gets "for free" the FMS list that will be added
later to the kernel.

Thanks,

Paolo

> +
> +	return data;
> +}
> +EXPORT_SYMBOL_GPL(kvm_get_core_capability);
> +
>  u64 kvm_get_arch_capabilities(void)
>  {
>  	u64 data;
> @@ -1227,6 +1239,9 @@ EXPORT_SYMBOL_GPL(kvm_get_arch_capabilities);
>  static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
>  {
>  	switch (msr->index) {
> +	case MSR_IA32_CORE_CAPABILITY:
> +		msr->data = kvm_get_core_capability();
> +		break;
>  	case MSR_IA32_ARCH_CAPABILITIES:
>  		msr->data = kvm_get_arch_capabilities();
>  		break;
>