aarch64: Add support for MTE

MTE has been supported in Linux since commit 673638f434ee ("KVM: arm64:
Expose KVM_ARM_CAP_MTE"), add support for it in kvmtool. MTE is enabled by
default.

Enabling the MTE capability incurs a cost, both in time (for each
translation fault the tags need to be cleared), and in space (the tags need
to be saved when a physical page is swapped out). This overhead is expected
to be negligible for most users, but for those cases where it matters
(like performance benchmarks), a --disable-mte option has been added.

Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20220328103328.18768-3-alexandru.elisei@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

6 files changed, 31 insertions, 0 deletions

diff --git a/arm/aarch32/include/kvm/kvm-arch.h b/arm/aarch32/include/kvm/kvm-arch.h
index bee2fc25..5616b27e 100644
--- a/arm/aarch32/include/kvm/kvm-arch.h
+++ b/arm/aarch32/include/kvm/kvm-arch.h
@@ -5,6 +5,9 @@
 
 #define kvm__arch_get_kern_offset(...)	0x8000
 
+struct kvm;
+static inline void kvm__arch_enable_mte(struct kvm *kvm) {}
+
 #define ARM_MAX_MEMORY(...)	ARM_LOMAP_MAX_MEMORY
 
 #define MAX_PAGE_SIZE	SZ_4K
diff --git a/arm/aarch64/include/kvm/kvm-arch.h b/arm/aarch64/include/kvm/kvm-arch.h
index 5e5ee412..9124f691 100644
--- a/arm/aarch64/include/kvm/kvm-arch.h
+++ b/arm/aarch64/include/kvm/kvm-arch.h
@@ -6,6 +6,7 @@
 struct kvm;
 unsigned long long kvm__arch_get_kern_offset(struct kvm *kvm, int fd);
 int kvm__arch_get_ipa_limit(struct kvm *kvm);
+void kvm__arch_enable_mte(struct kvm *kvm);
 
 #define ARM_MAX_MEMORY(kvm)	({					\
 	u64 max_ram;							\
diff --git a/arm/aarch64/include/kvm/kvm-config-arch.h b/arm/aarch64/include/kvm/kvm-config-arch.h
index a9b05766..3d39cd6d 100644
--- a/arm/aarch64/include/kvm/kvm-config-arch.h
+++ b/arm/aarch64/include/kvm/kvm-config-arch.h
@@ -6,6 +6,8 @@
 			"Run AArch32 guest"),				\
 	OPT_BOOLEAN('\0', "pmu", &(cfg)->has_pmuv3,			\
 			"Create PMUv3 device"),				\
+	OPT_BOOLEAN('\0', "disable-mte", &(cfg)->mte_disabled,		\
+			"Disable Memory Tagging Extension"),		\
 	OPT_U64('\0', "kaslr-seed", &(cfg)->kaslr_seed,			\
 			"Specify random seed for Kernel Address Space "	\
 			"Layout Randomization (KASLR)"),		\
diff --git a/arm/aarch64/kvm.c b/arm/aarch64/kvm.c
index 56a0aedc..28d608d9 100644
--- a/arm/aarch64/kvm.c
+++ b/arm/aarch64/kvm.c
@@ -81,3 +81,25 @@ int kvm__get_vm_type(struct kvm *kvm)
 
 	return KVM_VM_TYPE_ARM_IPA_SIZE(ipa_bits);
 }
+
+void kvm__arch_enable_mte(struct kvm *kvm)
+{
+	struct kvm_enable_cap cap = {
+		.cap = KVM_CAP_ARM_MTE,
+	};
+
+	if (kvm->cfg.arch.mte_disabled) {
+		pr_debug("MTE disabled by user");
+		return;
+	}
+
+	if (!kvm__supports_extension(kvm, KVM_CAP_ARM_MTE)) {
+		pr_debug("MTE capability not available");
+		return;
+	}
+
+	if (ioctl(kvm->vm_fd, KVM_ENABLE_CAP, &cap))
+		die_perror("KVM_ENABLE_CAP(KVM_CAP_ARM_MTE)");
+
+	pr_debug("MTE capability enabled");
+}
diff --git a/arm/include/arm-common/kvm-config-arch.h b/arm/include/arm-common/kvm-config-arch.h
index 9f97778d..cdcbf235 100644
--- a/arm/include/arm-common/kvm-config-arch.h
+++ b/arm/include/arm-common/kvm-config-arch.h
@@ -9,6 +9,7 @@ struct kvm_config_arch {
 	bool		virtio_trans_pci;
 	bool		aarch32_guest;
 	bool		has_pmuv3;
+	bool		mte_disabled;
 	u64		kaslr_seed;
 	enum irqchip_type irqchip;
 	u64		fw_addr;
diff --git a/arm/kvm.c b/arm/kvm.c
index 80d233f1..c5913000 100644
--- a/arm/kvm.c
+++ b/arm/kvm.c
@@ -86,6 +86,8 @@ void kvm__arch_init(struct kvm *kvm, const char *hugetlbfs_path, u64 ram_size)
 	/* Create the virtual GIC. */
 	if (gic__create(kvm, kvm->cfg.arch.irqchip))
 		die("Failed to create virtual GIC");
+
+	kvm__arch_enable_mte(kvm);
 }
 
 #define FDT_ALIGN	SZ_2M