linux-kernel - [PATCH v3 10/34] KVM: x86: hyper-v: Create a separate ring for L2 TLB flush

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Date:   Thu, 14 Apr 2022 15:19:49 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 10/34] KVM: x86: hyper-v: Create a separate ring for L2 TLB flush

To handle L2 TLB flush requests, KVM needs to use a separate ring from
regular (L1) Hyper-V TLB flush requests: e.g. when a request to flush
something in L2 is made, the target vCPU can transition from L2 to L1,
receive a request to flush a GVA for L1 and then try to enter L2 back.
The first request needs to be processed at this point. Similarly,
requests to flush GVAs in L1 must wait until L2 exits to L1.

No functional change as KVM doesn't handle L2 TLB flush requests from
L2 yet.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/include/asm/kvm_host.h |  8 +++++++-
 arch/x86/kvm/hyperv.c           |  8 +++++---
 arch/x86/kvm/hyperv.h           | 19 ++++++++++++++++---
 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b4dd2ff61658..058061621872 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -580,6 +580,12 @@ struct kvm_vcpu_hv_synic {
 
 #define KVM_HV_TLB_FLUSH_RING_SIZE (16)
 
+enum hv_tlb_flush_rings {
+	HV_L1_TLB_FLUSH_RING,
+	HV_L2_TLB_FLUSH_RING,
+	HV_NR_TLB_FLUSH_RINGS,
+};
+
 struct kvm_vcpu_hv_tlb_flush_entry {
 	u64 addr;
 	u64 flush_all:1;
@@ -612,7 +618,7 @@ struct kvm_vcpu_hv {
 		u32 syndbg_cap_eax; /* HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES.EAX */
 	} cpuid_cache;
 
-	struct kvm_vcpu_hv_tlb_flush_ring tlb_flush_ring;
+	struct kvm_vcpu_hv_tlb_flush_ring tlb_flush_ring[HV_NR_TLB_FLUSH_RINGS];
 };
 
 /* Xen HVM per vcpu emulation context */
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index aebbb598ad1d..1cef2b8f7001 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -956,7 +956,8 @@ static int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
 
 	hv_vcpu->vp_index = vcpu->vcpu_idx;
 
-	spin_lock_init(&hv_vcpu->tlb_flush_ring.write_lock);
+	for (i = 0; i < HV_NR_TLB_FLUSH_RINGS; i++)
+		spin_lock_init(&hv_vcpu->tlb_flush_ring[i].write_lock);
 
 	return 0;
 }
@@ -1852,7 +1853,8 @@ static void hv_tlb_flush_ring_enqueue(struct kvm_vcpu *vcpu, u64 *entries, int c
 	if (!hv_vcpu)
 		return;
 
-	tlb_flush_ring = &hv_vcpu->tlb_flush_ring;
+	/* kvm_hv_flush_tlb() is not ready to handle requests for L2s yet */
+	tlb_flush_ring = &hv_vcpu->tlb_flush_ring[HV_L1_TLB_FLUSH_RING];
 
 	spin_lock_irqsave(&tlb_flush_ring->write_lock, flags);
 
@@ -1921,7 +1923,7 @@ void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
 		return;
 	}
 
-	tlb_flush_ring = &hv_vcpu->tlb_flush_ring;
+	tlb_flush_ring = kvm_hv_get_tlb_flush_ring(vcpu);
 
 	/*
 	 * TLB flush must be performed on the target vCPU so 'read_idx'
diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index 6847caeaaf84..d59f96700104 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -22,6 +22,7 @@
 #define __ARCH_X86_KVM_HYPERV_H__
 
 #include <linux/kvm_host.h>
+#include "x86.h"
 
 /*
  * The #defines related to the synthetic debugger are required by KDNet, but
@@ -147,15 +148,27 @@ int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args);
 int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
 		     struct kvm_cpuid_entry2 __user *entries);
 
+static inline struct kvm_vcpu_hv_tlb_flush_ring *kvm_hv_get_tlb_flush_ring(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+	int i = !is_guest_mode(vcpu) ? HV_L1_TLB_FLUSH_RING :
+		HV_L2_TLB_FLUSH_RING;
+
+	/* KVM does not handle L2 TLB flush requests yet */
+	WARN_ON_ONCE(i != HV_L1_TLB_FLUSH_RING);
+
+	return &hv_vcpu->tlb_flush_ring[i];
+}
 
 static inline void kvm_hv_vcpu_empty_flush_tlb(struct kvm_vcpu *vcpu)
 {
-	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+	struct kvm_vcpu_hv_tlb_flush_ring *tlb_flush_ring;
 
-	if (!hv_vcpu)
+	if (!to_hv_vcpu(vcpu))
 		return;
 
-	hv_vcpu->tlb_flush_ring.read_idx = hv_vcpu->tlb_flush_ring.write_idx;
+	tlb_flush_ring = kvm_hv_get_tlb_flush_ring(vcpu);
+	tlb_flush_ring->read_idx = tlb_flush_ring->write_idx;
 }
 void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu);
 
-- 
2.35.1