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From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Paolo Bonzini <pbonzini@redhat.com>,
        David Matlack <dmatlack@google.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Suleiman Souhlal <suleiman@google.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: [PATCHV2 3/3] KVM: x86: add KVM_SET_MMU_PREFETCH ioctl
Date:   Wed, 20 Oct 2021 00:32:14 +0900
Message-Id: <20211019153214.109519-4-senozhatsky@chromium.org>
In-Reply-To: <20211019153214.109519-1-senozhatsky@chromium.org>
References: <20211019153214.109519-1-senozhatsky@chromium.org>
MIME-Version: 1.0
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This ioctl lets user-space set the number of PTEs KVM will
prefetch:

-  pte_prefetch 8

             VM-EXIT    Samples  Samples%     Time%    Min Time    Max Time         Avg time

       EPT_VIOLATION     760998    54.85%     7.23%      0.92us  31765.89us      7.78us ( +-   1.46% )
           MSR_WRITE     170599    12.30%     0.53%      0.60us   3334.13us      2.52us ( +-   0.86% )
  EXTERNAL_INTERRUPT     159510    11.50%     1.65%      0.49us  43705.81us      8.45us ( +-   7.54% )
[..]

Total Samples:1387305, Total events handled time:81900258.99us.

- pte_prefetch 16

             VM-EXIT    Samples  Samples%     Time%    Min Time    Max Time         Avg time

       EPT_VIOLATION     658064    52.58%     7.04%      0.91us  17022.84us      8.34us ( +-   1.52% )
           MSR_WRITE     163776    13.09%     0.54%      0.56us   5192.10us      2.57us ( +-   1.25% )
  EXTERNAL_INTERRUPT     144588    11.55%     1.62%      0.48us  97410.16us      8.75us ( +-  11.44% )
[..]

Total Samples:1251546, Total events handled time:77956187.56us.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 Documentation/virt/kvm/api.rst | 21 +++++++++++++++++++++
 arch/x86/kvm/x86.c             | 29 +++++++++++++++++++++++++++++
 include/uapi/linux/kvm.h       |  4 ++++
 3 files changed, 54 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 0c0bf26426b3..b06b7c11a430 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5473,6 +5473,17 @@ the trailing ``'\0'``, is indicated by ``name_size`` in the header.
 The Stats Data block contains an array of 64-bit values in the same order
 as the descriptors in Descriptors block.
 
+4.134 KVM SET MMU PREFETCH
+----------------------
+
+:Capability: KVM_CAP_MMU PREFETCH
+:Architectures: x86
+:Type: vm ioctl
+:Parameters: int value (in)
+:Returns: 0 on success, error code otherwise
+
+Sets the maximum number of PTEs KVM will try to prefetch.
+
 5. The kvm_run structure
 ========================
 
@@ -7440,3 +7451,13 @@ The argument to KVM_ENABLE_CAP is also a bitmask, and must be a subset
 of the result of KVM_CHECK_EXTENSION.  KVM will forward to userspace
 the hypercalls whose corresponding bit is in the argument, and return
 ENOSYS for the others.
+
+8.35 KVM_CAP_MMU_PTE_PREFETCH
+---------------------------
+
+:Capability: KVM_CAP_MMU_PTE_PREFETCH
+:Architectures: x86
+:Parameters: args[0] - the number of PTEs to prefetch
+
+Sets the maximum number of PTEs KVM will prefetch. The value must be power
+of two and within (0, 128] range.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4805960a89e6..e1b2224c4176 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4030,6 +4030,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_VM_COPY_ENC_CONTEXT_FROM:
 	case KVM_CAP_SREGS2:
 	case KVM_CAP_EXIT_ON_EMULATION_FAILURE:
+	case KVM_CAP_MMU_PTE_PREFETCH:
 		r = 1;
 		break;
 	case KVM_CAP_EXIT_HYPERCALL:
@@ -5831,6 +5832,25 @@ int kvm_arch_pm_notifier(struct kvm *kvm, unsigned long state)
 }
 #endif /* CONFIG_HAVE_KVM_PM_NOTIFIER */
 
+static int kvm_arch_mmu_pte_prefetch(struct kvm *kvm, unsigned int num_pages)
+{
+	struct kvm_vcpu *vcpu;
+	int i, ret;
+
+	mutex_lock(&kvm->lock);
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		ret = kvm_set_pte_prefetch(vcpu, num_pages);
+		if (ret) {
+			kvm_err("Failed to set PTE prefetch on VCPU%d: %d\n",
+				vcpu->vcpu_id, ret);
+			break;
+		}
+	}
+	mutex_unlock(&kvm->lock);
+
+	return ret;
+}
+
 static int kvm_vm_ioctl_get_clock(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_clock_data data;
@@ -6169,6 +6189,15 @@ long kvm_arch_vm_ioctl(struct file *filp,
 	case KVM_X86_SET_MSR_FILTER:
 		r = kvm_vm_ioctl_set_msr_filter(kvm, argp);
 		break;
+	case KVM_SET_MMU_PREFETCH: {
+		u64 val;
+
+		r = -EFAULT;
+		if (copy_from_user(&val, argp, sizeof(val)))
+			goto out;
+		r = kvm_arch_mmu_pte_prefetch(kvm, val);
+		break;
+	}
 	default:
 		r = -ENOTTY;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 322b4b588d75..0782eb4c424d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1120,6 +1120,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_BINARY_STATS_FD 203
 #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
 #define KVM_CAP_ARM_MTE 205
+#define KVM_CAP_MMU_PTE_PREFETCH 206
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -2015,4 +2016,7 @@ struct kvm_stats_desc {
 
 #define KVM_GET_STATS_FD  _IO(KVMIO,  0xce)
 
+/* Set number of PTEs to prefetch */
+#define KVM_SET_MMU_PREFETCH      _IOW(KVMIO, 0xcf, __u64)
+
 #endif /* __LINUX_KVM_H */
-- 
2.33.0.1079.g6e70778dc9-goog