linux-kernel - Re: [PATCH v4 1/3] KVM: x86: add support for user wait instructions

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Message-ID: <7f6bc0fa-abcd-ce0a-19a0-a5767d094181@linux.intel.com>
Date:   Wed, 19 Jun 2019 14:23:36 +0800
From:   Xiaoyao Li <xiaoyao.li@...ux.intel.com>
To:     Tao Xu <tao3.xu@...el.com>, pbonzini@...hat.com,
        rkrcmar@...hat.com, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        sean.j.christopherson@...el.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        fenghua.yu@...el.com, jingqi.liu@...el.com
Subject: Re: [PATCH v4 1/3] KVM: x86: add support for user wait instructions



On 6/19/2019 2:09 PM, Tao Xu wrote:
> UMONITOR, UMWAIT and TPAUSE are a set of user wait instructions.
> This patch adds support for user wait instructions in KVM. Availability
> of the user wait instructions is indicated by the presence of the CPUID
> feature flag WAITPKG CPUID.0x07.0x0:ECX[5]. User wait instructions may
> be executed at any privilege level, and use IA32_UMWAIT_CONTROL MSR to
> set the maximum time.
> 
> The behavior of user wait instructions in VMX non-root operation is
> determined first by the setting of the "enable user wait and pause"
> secondary processor-based VM-execution control bit 26.
> 	If the VM-execution control is 0, UMONITOR/UMWAIT/TPAUSE cause
> an invalid-opcode exception (#UD).
> 	If the VM-execution control is 1, treatment is based on the
> setting of the “RDTSC exiting” VM-execution control. Because KVM never
> enables RDTSC exiting, if the instruction causes a delay, the amount of
> time delayed is called here the physical delay. The physical delay is
> first computed by determining the virtual delay. If
> IA32_UMWAIT_CONTROL[31:2] is zero, the virtual delay is the value in
> EDX:EAX minus the value that RDTSC would return; if
> IA32_UMWAIT_CONTROL[31:2] is not zero, the virtual delay is the minimum
> of that difference and AND(IA32_UMWAIT_CONTROL,FFFFFFFCH).
> 
> Because umwait and tpause can put a (psysical) CPU into a power saving
> state, by default we dont't expose it to kvm and enable it only when
> guest CPUID has it.
> 
> Detailed information about user wait instructions can be found in the
> latest Intel 64 and IA-32 Architectures Software Developer's Manual.
> 
> Co-developed-by: Jingqi Liu <jingqi.liu@...el.com>
> Signed-off-by: Jingqi Liu <jingqi.liu@...el.com>
> Signed-off-by: Tao Xu <tao3.xu@...el.com>
> ---
> 
> no changes in v4.
> ---
>   arch/x86/include/asm/vmx.h      | 1 +
>   arch/x86/kvm/cpuid.c            | 2 +-
>   arch/x86/kvm/vmx/capabilities.h | 6 ++++++
>   arch/x86/kvm/vmx/vmx.c          | 4 ++++
>   4 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index a39136b0d509..8f00882664d3 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -69,6 +69,7 @@
>   #define SECONDARY_EXEC_PT_USE_GPA		0x01000000
>   #define SECONDARY_EXEC_MODE_BASED_EPT_EXEC	0x00400000
>   #define SECONDARY_EXEC_TSC_SCALING              0x02000000
> +#define SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE	0x04000000
>   
>   #define PIN_BASED_EXT_INTR_MASK                 0x00000001
>   #define PIN_BASED_NMI_EXITING                   0x00000008
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index e18a9f9f65b5..48bd851a6ae5 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -405,7 +405,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>   		F(AVX512VBMI) | F(LA57) | F(PKU) | 0 /*OSPKE*/ |
>   		F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) |
>   		F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) |
> -		F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B);
> +		F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B) | 0 /*WAITPKG*/;
>   
>   	/* cpuid 7.0.edx*/
>   	const u32 kvm_cpuid_7_0_edx_x86_features =
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index d6664ee3d127..fd77e17651b4 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -253,6 +253,12 @@ static inline bool cpu_has_vmx_tsc_scaling(void)
>   		SECONDARY_EXEC_TSC_SCALING;
>   }
>   
> +static inline bool vmx_waitpkg_supported(void)
> +{
> +	return vmcs_config.cpu_based_2nd_exec_ctrl &
> +		SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE;

Shouldn't it be
	return vmx->secondary_exec_control &
                 SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE;   ?

> +}
> +
>   static inline bool cpu_has_vmx_apicv(void)
>   {
>   	return cpu_has_vmx_apic_register_virt() &&
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b93e36ddee5e..b35bfac30a34 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2250,6 +2250,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>   			SECONDARY_EXEC_RDRAND_EXITING |
>   			SECONDARY_EXEC_ENABLE_PML |
>   			SECONDARY_EXEC_TSC_SCALING |
> +			SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE |
>   			SECONDARY_EXEC_PT_USE_GPA |
>   			SECONDARY_EXEC_PT_CONCEAL_VMX |
>   			SECONDARY_EXEC_ENABLE_VMFUNC |
> @@ -3987,6 +3988,9 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
>   		}
>   	}
>   
> +	if (!guest_cpuid_has(vcpu, X86_FEATURE_WAITPKG))
> +		exec_control &= ~SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE;
> +
>   	vmx->secondary_exec_control = exec_control;
>   }
>   
>