Re: [patch 2/3] kvm: x86: add host poll control msrs

[Paolo Bonzini <pbonzini@redhat.com>]

> Add an MSRs which allows the guest to disable 
> host polling (specifically the cpuidle-haltpoll, 
> when performing polling in the guest, disables
> host side polling).
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Queued this patch while waiting for Rafal's review.

Paolo

> ---
>  Documentation/virtual/kvm/msr.txt    |    9 +++++++++
>  arch/x86/include/asm/kvm_host.h      |    2 ++
>  arch/x86/include/uapi/asm/kvm_para.h |    2 ++
>  arch/x86/kvm/Kconfig                 |    1 +
>  arch/x86/kvm/cpuid.c                 |    3 ++-
>  arch/x86/kvm/x86.c                   |   23 +++++++++++++++++++++++
>  6 files changed, 39 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.git/Documentation/virtual/kvm/msr.txt
> ===================================================================
> --- linux-2.6.git.orig/Documentation/virtual/kvm/msr.txt	2018-05-18 15:40:19.697438928 -0300
> +++ linux-2.6.git/Documentation/virtual/kvm/msr.txt	2019-06-03 19:37:49.618543527 -0300
> @@ -273,3 +273,12 @@
>  	guest must both read the least significant bit in the memory area and
>  	clear it using a single CPU instruction, such as test and clear, or
>  	compare and exchange.
> +
> +MSR_KVM_POLL_CONTROL: 0x4b564d05
> +	Control host side polling.
> +
> +	data: Bit 0 enables (1) or disables (0) host halt poll
> +	logic.
> +	KVM guests can disable host halt polling when performing
> +	polling themselves.
> +
> Index: linux-2.6.git/arch/x86/include/asm/kvm_host.h
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/include/asm/kvm_host.h	2019-05-29 14:46:14.516005546 -0300
> +++ linux-2.6.git/arch/x86/include/asm/kvm_host.h	2019-06-03 19:37:49.619543530 -0300
> @@ -755,6 +755,8 @@
>  		struct gfn_to_hva_cache data;
>  	} pv_eoi;
>  
> +	u64 msr_kvm_poll_control;
> +
>  	/*
>  	 * Indicate whether the access faults on its page table in guest
>  	 * which is set when fix page fault and used to detect unhandeable
> Index: linux-2.6.git/arch/x86/include/uapi/asm/kvm_para.h
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/include/uapi/asm/kvm_para.h	2019-01-04 12:07:15.936947406 -0200
> +++ linux-2.6.git/arch/x86/include/uapi/asm/kvm_para.h	2019-06-03 19:37:49.620543534 -0300
> @@ -29,6 +29,7 @@
>  #define KVM_FEATURE_PV_TLB_FLUSH	9
>  #define KVM_FEATURE_ASYNC_PF_VMEXIT	10
>  #define KVM_FEATURE_PV_SEND_IPI	11
> +#define KVM_FEATURE_POLL_CONTROL	12
>  
>  #define KVM_HINTS_REALTIME      0
>  
> @@ -47,6 +48,7 @@
>  #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
>  #define MSR_KVM_STEAL_TIME  0x4b564d03
>  #define MSR_KVM_PV_EOI_EN      0x4b564d04
> +#define MSR_KVM_POLL_CONTROL	0x4b564d05
>  
>  struct kvm_steal_time {
>  	__u64 steal;
> Index: linux-2.6.git/arch/x86/kvm/Kconfig
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/kvm/Kconfig	2019-05-29 14:46:14.530005593 -0300
> +++ linux-2.6.git/arch/x86/kvm/Kconfig	2019-06-03 19:37:49.620543534 -0300
> @@ -41,6 +41,7 @@
>  	select PERF_EVENTS
>  	select HAVE_KVM_MSI
>  	select HAVE_KVM_CPU_RELAX_INTERCEPT
> +	select HAVE_KVM_NO_POLL
>  	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
>  	select KVM_VFIO
>  	select SRCU
> Index: linux-2.6.git/arch/x86/kvm/cpuid.c
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/kvm/cpuid.c	2019-05-29 14:46:14.530005593 -0300
> +++ linux-2.6.git/arch/x86/kvm/cpuid.c	2019-06-03 19:37:49.621543537 -0300
> @@ -643,7 +643,8 @@
>  			     (1 << KVM_FEATURE_PV_UNHALT) |
>  			     (1 << KVM_FEATURE_PV_TLB_FLUSH) |
>  			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT) |
> -			     (1 << KVM_FEATURE_PV_SEND_IPI);
> +			     (1 << KVM_FEATURE_PV_SEND_IPI) |
> +			     (1 << KVM_FEATURE_POLL_CONTROL);
>  
>  		if (sched_info_on())
>  			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
> Index: linux-2.6.git/arch/x86/kvm/x86.c
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/kvm/x86.c	2019-05-29 14:46:14.537005616 -0300
> +++ linux-2.6.git/arch/x86/kvm/x86.c	2019-06-03 19:37:49.624543547 -0300
> @@ -1177,6 +1177,7 @@
>  	MSR_IA32_POWER_CTL,
>  
>  	MSR_K7_HWCR,
> +	MSR_KVM_POLL_CONTROL,
>  };
>  
>  static unsigned num_emulated_msrs;
> @@ -2628,6 +2629,14 @@
>  			return 1;
>  		break;
>  
> +	case MSR_KVM_POLL_CONTROL:
> +		/* only enable bit supported */
> +		if (data & (-1ULL << 1))
> +			return 1;
> +
> +		vcpu->arch.msr_kvm_poll_control = data;
> +		break;
> +
>  	case MSR_IA32_MCG_CTL:
>  	case MSR_IA32_MCG_STATUS:
>  	case MSR_IA32_MC0_CTL ... MSR_IA32_MCx_CTL(KVM_MAX_MCE_BANKS) - 1:
> @@ -2877,6 +2886,9 @@
>  	case MSR_KVM_PV_EOI_EN:
>  		msr_info->data = vcpu->arch.pv_eoi.msr_val;
>  		break;
> +	case MSR_KVM_POLL_CONTROL:
> +		msr_info->data = vcpu->arch.msr_kvm_poll_control;
> +		break;
>  	case MSR_IA32_P5_MC_ADDR:
>  	case MSR_IA32_P5_MC_TYPE:
>  	case MSR_IA32_MCG_CAP:
> @@ -8874,6 +8886,10 @@
>  	msr.host_initiated = true;
>  	kvm_write_tsc(vcpu, &msr);
>  	vcpu_put(vcpu);
> +
> +	/* poll control enabled by default */
> +	vcpu->arch.msr_kvm_poll_control = 1;
> +
>  	mutex_unlock(&vcpu->mutex);
>  
>  	if (!kvmclock_periodic_sync)
> @@ -9948,6 +9964,13 @@
>  }
>  EXPORT_SYMBOL_GPL(kvm_vector_hashing_enabled);
>  
> +bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
> +{
> +	return (vcpu->arch.msr_kvm_poll_control & 1) == 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_arch_no_poll);
> +
> +
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
> 
>