Message-Id: <20210825161815.266051-3-alexandru.elisei@arm.com>
Date:   Wed, 25 Aug 2021 17:17:38 +0100
From:   Alexandru Elisei <alexandru.elisei@....com>
To:     maz@...nel.org, james.morse@....com, suzuki.poulose@....com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        will@...nel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v4 02/39] KVM: arm64: Add lock/unlock memslot user API

Stage 2 faults triggered by the profiling buffer attempting to write to
memory are reported by the SPE hardware by asserting a buffer management
event interrupt. Interrupts are by their nature asynchronous, which means
that the guest might have changed its stage 1 translation tables since the
attempted write. SPE reports the guest virtual address that caused the data
abort, not the IPA, which means that KVM would have to walk the guest's
stage 1 tables to find the IPA. Using the AT instruction to walk the
guest's tables in hardware is not an option because it doesn't report the
IPA in the case of a stage 2 fault on a stage 1 table walk.

Avoid both issues by pre-mapping the guest memory at stage 2. This is being
done by adding a capability that allows the user to pin the memory backing
a memslot. The same capability can be used to unlock a memslot, which
unpins the pages associated with the memslot, but doesn't unmap the IPA
range from stage 2; in this case, the addresses will be unmapped from stage
2 via the MMU notifiers when the process' address space changes.

For now, the capability doesn't actually do anything other than checking
that the usage is correct; the memory operations will be added in future
patches.

Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
---
 Documentation/virt/kvm/api.rst   | 56 +++++++++++++++++++++++
 arch/arm64/include/asm/kvm_mmu.h |  3 ++
 arch/arm64/kvm/arm.c             | 42 ++++++++++++++++--
 arch/arm64/kvm/mmu.c             | 76 ++++++++++++++++++++++++++++++++
 include/uapi/linux/kvm.h         |  8 ++++
 5 files changed, 181 insertions(+), 4 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index dae68e68ca23..741327ef06b0 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6682,6 +6682,62 @@ MAP_SHARED mmap will result in an -EINVAL return.
 When enabled the VMM may make use of the ``KVM_ARM_MTE_COPY_TAGS`` ioctl to
 perform a bulk copy of tags to/from the guest.
 
+7.29 KVM_CAP_ARM_LOCK_USER_MEMORY_REGION
+----------------------------------------
+
+:Architectures: arm64
+:Target: VM
+:Parameters: flags is one of KVM_ARM_LOCK_USER_MEMORY_REGION_FLAGS_LOCK or
+                     KVM_ARM_LOCK_USER_MEMORY_REGION_FLAGS_UNLOCK
+             args[0] is the slot number
+             args[1] specifies the permisions when the memslot is locked or if
+                     all memslots should be unlocked
+
+The presence of this capability indicates that KVM supports locking the memory
+associated with the memslot, and unlocking a previously locked memslot.
+
+The 'flags' parameter is defined as follows:
+
+7.29.1 KVM_ARM_LOCK_USER_MEMORY_REGION_FLAGS_LOCK
+-------------------------------------------------
+
+:Capability: 'flags' parameter to KVM_CAP_ARM_LOCK_USER_MEMORY_REGION
+:Architectures: arm64
+:Target: VM
+:Parameters: args[0] contains the memory slot number
+             args[1] contains the permissions for the locked memory:
+                     KVM_ARM_LOCK_MEMORY_READ (mandatory) to map it with
+                     read permissions and KVM_ARM_LOCK_MEMORY_WRITE
+                     (optional) with write permissions
+:Returns: 0 on success; negative error code on failure
+
+Enabling this capability causes the memory described by the memslot to be
+pinned in the process address space and the corresponding stage 2 IPA range
+mapped at stage 2. The permissions specified in args[1] apply to both
+mappings. The memory pinned with this capability counts towards the max
+locked memory limit for the current process.
+
+The capability must be enabled before any VCPUs have run. The virtual memory
+range described by the memslot must be mapped in the userspace process without
+any gaps. It is considered an error if write permissions are specified for a
+memslot which logs dirty pages.
+
+7.29.2 KVM_ARM_LOCK_USER_MEMORY_REGION_FLAGS_UNLOCK
+---------------------------------------------------
+
+:Capability: 'flags' parameter to KVM_CAP_ARM_LOCK_USER_MEMORY_REGION
+:Architectures: arm64
+:Target: VM
+:Parameters: args[0] contains the memory slot number
+             args[1] optionally contains the flag KVM_ARM_UNLOCK_MEM_ALL,
+                     which unlocks all previously locked memslots.
+:Returns: 0 on success; negative error code on failure
+
+Enabling this capability causes the memory pinned when locking the memslot
+specified in args[0] to be unpinned, or, optionally, the memory associated
+with all locked memslots, to be unpinned. The IPA range is not unmapped
+from stage 2.
+
 8. Other capabilities.
 ======================
 
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index b52c5c4b9a3d..ef079b5eb475 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -216,6 +216,9 @@ static inline void __invalidate_icache_guest_page(void *va, size_t size)
 void kvm_set_way_flush(struct kvm_vcpu *vcpu);
 void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool was_enabled);
 
+int kvm_mmu_lock_memslot(struct kvm *kvm, u64 slot, u64 flags);
+int kvm_mmu_unlock_memslot(struct kvm *kvm, u64 slot, u64 flags);
+
 static inline unsigned int kvm_get_vmid_bits(void)
 {
 	int reg = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index ddace63528f1..57ac97b30b3d 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -80,16 +80,43 @@ int kvm_arch_check_processor_compat(void *opaque)
 	return 0;
 }
 
+static int kvm_arm_lock_memslot_supported(void)
+{
+	return 0;
+}
+
+static int kvm_lock_user_memory_region_ioctl(struct kvm *kvm,
+					     struct kvm_enable_cap *cap)
+{
+	u64 slot, flags;
+	u32 action;
+
+	if (cap->args[2] || cap->args[3])
+		return -EINVAL;
+
+	slot = cap->args[0];
+	flags = cap->args[1];
+	action = cap->flags;
+
+	switch (action) {
+	case KVM_ARM_LOCK_USER_MEMORY_REGION_FLAGS_LOCK:
+		return kvm_mmu_lock_memslot(kvm, slot, flags);
+	case KVM_ARM_LOCK_USER_MEMORY_REGION_FLAGS_UNLOCK:
+		return kvm_mmu_unlock_memslot(kvm, slot, flags);
+	default:
+		return -EINVAL;
+	}
+}
+
 int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 			    struct kvm_enable_cap *cap)
 {
 	int r;
 
-	if (cap->flags)
-		return -EINVAL;
-
 	switch (cap->cap) {
 	case KVM_CAP_ARM_NISV_TO_USER:
+		if (cap->flags)
+			return -EINVAL;
 		r = 0;
 		kvm->arch.return_nisv_io_abort_to_user = true;
 		break;
@@ -99,6 +126,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		r = 0;
 		kvm->arch.mte_enabled = true;
 		break;
+	case KVM_CAP_ARM_LOCK_USER_MEMORY_REGION:
+		if (!kvm_arm_lock_memslot_supported())
+			return -EINVAL;
+		r = kvm_lock_user_memory_region_ioctl(kvm, cap);
+		break;
 	default:
 		r = -EINVAL;
 		break;
@@ -166,7 +198,6 @@ vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 	return VM_FAULT_SIGBUS;
 }
 
-
 /**
  * kvm_arch_destroy_vm - destroy the VM data structure
  * @kvm:	pointer to the KVM struct
@@ -274,6 +305,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ARM_PTRAUTH_GENERIC:
 		r = system_has_full_ptr_auth();
 		break;
+	case KVM_CAP_ARM_LOCK_USER_MEMORY_REGION:
+		r = kvm_arm_lock_memslot_supported();
+		break;
 	default:
 		r = 0;
 	}
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 0625bf2353c2..689b24cb0f10 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1244,6 +1244,82 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	return ret;
 }
 
+int kvm_mmu_lock_memslot(struct kvm *kvm, u64 slot, u64 flags)
+{
+	struct kvm_memory_slot *memslot;
+	struct kvm_vcpu *vcpu;
+	int i, ret;
+
+	if (slot >= KVM_MEM_SLOTS_NUM)
+		return -EINVAL;
+
+	if (!(flags & KVM_ARM_LOCK_MEM_READ))
+		return -EINVAL;
+
+	mutex_lock(&kvm->lock);
+
+	if (!kvm_lock_all_vcpus(kvm)) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		if (vcpu->arch.has_run_once) {
+			ret = -EBUSY;
+			goto out_unlock_vcpus;
+		}
+	}
+
+	mutex_lock(&kvm->slots_lock);
+
+	memslot = id_to_memslot(kvm_memslots(kvm), slot);
+	if (!memslot) {
+		ret = -EINVAL;
+		goto out_unlock_slots;
+	}
+	if ((flags & KVM_ARM_LOCK_MEM_WRITE) &&
+	    ((memslot->flags & KVM_MEM_READONLY) || memslot->dirty_bitmap)) {
+		ret = -EPERM;
+		goto out_unlock_slots;
+	}
+
+	ret = -EINVAL;
+
+out_unlock_slots:
+	mutex_unlock(&kvm->slots_lock);
+out_unlock_vcpus:
+	kvm_unlock_all_vcpus(kvm);
+out:
+	mutex_unlock(&kvm->lock);
+	return ret;
+}
+
+int kvm_mmu_unlock_memslot(struct kvm *kvm, u64 slot, u64 flags)
+{
+	struct kvm_memory_slot *memslot;
+	int ret;
+
+	if (flags & KVM_ARM_UNLOCK_MEM_ALL)
+		return -EINVAL;
+
+	if (slot >= KVM_MEM_SLOTS_NUM)
+		return -EINVAL;
+
+	mutex_lock(&kvm->slots_lock);
+
+	memslot = id_to_memslot(kvm_memslots(kvm), slot);
+	if (!memslot) {
+		ret = -EINVAL;
+		goto out_unlock_slots;
+	}
+
+	ret = -EINVAL;
+
+out_unlock_slots:
+	mutex_unlock(&kvm->slots_lock);
+	return ret;
+}
+
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	if (!kvm->arch.mmu.pgt)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d9e4aabcb31a..bcf62c7bdd2d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1112,6 +1112,7 @@ 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_ARM_LOCK_USER_MEMORY_REGION 206
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1459,6 +1460,13 @@ struct kvm_s390_ucas_mapping {
 #define KVM_PPC_SVM_OFF		  _IO(KVMIO,  0xb3)
 #define KVM_ARM_MTE_COPY_TAGS	  _IOR(KVMIO,  0xb4, struct kvm_arm_copy_mte_tags)
 
+/* Used by KVM_CAP_ARM_LOCK_USER_MEMORY_REGION */
+#define KVM_ARM_LOCK_USER_MEMORY_REGION_FLAGS_LOCK	(1 << 0)
+#define   KVM_ARM_LOCK_MEM_READ				(1 << 0)
+#define   KVM_ARM_LOCK_MEM_WRITE			(1 << 1)
+#define KVM_ARM_LOCK_USER_MEMORY_REGION_FLAGS_UNLOCK	(1 << 1)
+#define   KVM_ARM_UNLOCK_MEM_ALL			(1 << 0)
+
 /* ioctl for vm fd */
 #define KVM_CREATE_DEVICE	  _IOWR(KVMIO,  0xe0, struct kvm_create_device)
 
-- 
2.33.0

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