Re: [kvmtool PATCH v2 2/2] aarch64: Add support for MTE

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Hi Alexandru,

On 3/24/22 11:39 AM, Alexandru Elisei wrote:
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 they matter
(like performance benchmarks), a --disable-mte option has been added.

Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---
  arm/aarch32/include/kvm/kvm-arch.h        |  3 +++
  arm/aarch64/include/kvm/kvm-arch.h        |  1 +
  arm/aarch64/include/kvm/kvm-config-arch.h |  2 ++
  arm/aarch64/kvm.c                         | 23 +++++++++++++++++++++++
  arm/include/arm-common/kvm-config-arch.h  |  1 +
  arm/kvm.c                                 |  2 ++
  6 files changed, 32 insertions(+)

diff --git a/arm/aarch32/include/kvm/kvm-arch.h b/arm/aarch32/include/kvm/kvm-arch.h
index bee2fc255a82..5616b27e257e 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 5e5ee41211ed..9124f6919d0f 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 04be43dfa9b2..df4a15ff00a7 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 capability"),	\
  	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 56a0aedc263d..1035171a00f0 100644
--- a/arm/aarch64/kvm.c
+++ b/arm/aarch64/kvm.c
@@ -81,3 +81,26 @@ 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 capability disabled by user");
+		return;
+	}

Nitpick:  I'd move that bellow capability check, so it'd appear only in
setups which support MTE

+
+	if (!kvm__supports_extension(kvm, KVM_CAP_ARM_MTE)) {
+		kvm->cfg.arch.mte_disabled = true;
+		pr_debug("MTE capability not present");
+		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 5734c46ab9e6..f2049994d859 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 80d233f13d0b..c5913000e1ed 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

FWIW:

Reviewed-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>
Tested-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>


Thanks!

Vladimir




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