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Message-Id: <20210825161815.266051-7-alexandru.elisei@arm.com>
Date: Wed, 25 Aug 2021 17:17:42 +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 06/39] KVM: arm64: Delay tag scrubbing for locked memslots until a VCPU runs
When an MTE-enabled guest first accesses a physical page, that page must be
scrubbed for tags. This is normally done by KVM on a translation fault, but
with locked memslots we will not get translation faults. So far, this has
been handled by forbidding userspace to enable the MTE capability after
locking a memslot.
Remove this constraint by deferring tag cleaning until the first VCPU is
run, similar to how KVM handles cache maintenance operations.
When userspace resets a VCPU, KVM again performs cache maintenance
operations on locked memslots because userspace might have modified the
guest memory. Clean the tags the next time a VCPU is run for the same
reason.
Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
---
arch/arm64/include/asm/kvm_host.h | 7 ++-
arch/arm64/include/asm/kvm_mmu.h | 2 +-
arch/arm64/kvm/arm.c | 29 ++--------
arch/arm64/kvm/mmu.c | 92 ++++++++++++++++++++++++++-----
4 files changed, 87 insertions(+), 43 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 68905bd47f85..a57f33368a3e 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -113,9 +113,10 @@ struct kvm_arch_memory_slot {
};
/* kvm->arch.mmu_pending_ops flags */
-#define KVM_LOCKED_MEMSLOT_FLUSH_DCACHE 0
-#define KVM_LOCKED_MEMSLOT_INVAL_ICACHE 1
-#define KVM_MAX_MMU_PENDING_OPS 2
+#define KVM_LOCKED_MEMSLOT_FLUSH_DCACHE 0
+#define KVM_LOCKED_MEMSLOT_INVAL_ICACHE 1
+#define KVM_LOCKED_MEMSLOT_SANITISE_TAGS 2
+#define KVM_MAX_MMU_PENDING_OPS 3
struct kvm_arch {
struct kvm_s2_mmu mmu;
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 525c223e769f..9fcdd2580f6e 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -222,7 +222,7 @@ int kvm_mmu_unlock_memslot(struct kvm *kvm, u64 slot, u64 flags);
#define kvm_mmu_has_pending_ops(kvm) \
(!bitmap_empty(&(kvm)->arch.mmu_pending_ops, KVM_MAX_MMU_PENDING_OPS))
-void kvm_mmu_perform_pending_ops(struct kvm *kvm);
+int kvm_mmu_perform_pending_ops(struct kvm *kvm);
static inline unsigned int kvm_get_vmid_bits(void)
{
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 144c982912d8..c47e96ae4f7c 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -108,25 +108,6 @@ static int kvm_lock_user_memory_region_ioctl(struct kvm *kvm,
}
}
-static bool kvm_arm_has_locked_memslots(struct kvm *kvm)
-{
- struct kvm_memslots *slots = kvm_memslots(kvm);
- struct kvm_memory_slot *memslot;
- bool has_locked_memslots = false;
- int idx;
-
- idx = srcu_read_lock(&kvm->srcu);
- kvm_for_each_memslot(memslot, slots) {
- if (memslot->arch.flags & KVM_MEMSLOT_LOCK_MASK) {
- has_locked_memslots = true;
- break;
- }
- }
- srcu_read_unlock(&kvm->srcu, idx);
-
- return has_locked_memslots;
-}
-
int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
struct kvm_enable_cap *cap)
{
@@ -142,9 +123,6 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
case KVM_CAP_ARM_MTE:
if (!system_supports_mte() || kvm->created_vcpus)
return -EINVAL;
- if (kvm_arm_lock_memslot_supported() &&
- kvm_arm_has_locked_memslots(kvm))
- return -EPERM;
r = 0;
kvm->arch.mte_enabled = true;
break;
@@ -829,8 +807,11 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
if (unlikely(!kvm_vcpu_initialized(vcpu)))
return -ENOEXEC;
- if (unlikely(kvm_mmu_has_pending_ops(vcpu->kvm)))
- kvm_mmu_perform_pending_ops(vcpu->kvm);
+ if (unlikely(kvm_mmu_has_pending_ops(vcpu->kvm))) {
+ ret = kvm_mmu_perform_pending_ops(vcpu->kvm);
+ if (ret)
+ return ret;
+ }
ret = kvm_vcpu_first_run_init(vcpu);
if (ret)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index f1f8a87550d1..cd44b6f2c53e 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -566,6 +566,10 @@ void stage2_unmap_vm(struct kvm *kvm)
&kvm->arch.mmu_pending_ops);
set_bit(KVM_LOCKED_MEMSLOT_INVAL_ICACHE,
&kvm->arch.mmu_pending_ops);
+ if (kvm_has_mte(kvm)) {
+ set_bit(KVM_LOCKED_MEMSLOT_SANITISE_TAGS,
+ &kvm->arch.mmu_pending_ops);
+ }
continue;
}
stage2_unmap_memslot(kvm, memslot);
@@ -909,6 +913,58 @@ static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
return 0;
}
+static int sanitise_mte_tags_memslot(struct kvm *kvm,
+ struct kvm_memory_slot *memslot)
+{
+ unsigned long hva, slot_size, slot_end;
+ struct kvm_memory_slot_page *entry;
+ struct page *page;
+ int ret = 0;
+
+ if (!kvm_has_mte(kvm))
+ return 0;
+
+ hva = memslot->userspace_addr;
+ slot_size = memslot->npages << PAGE_SHIFT;
+ slot_end = hva + slot_size;
+
+ /* First check that the VMAs spanning the memslot are not shared... */
+ do {
+ struct vm_area_struct *vma;
+
+ vma = find_vma_intersection(current->mm, hva, slot_end);
+ /* The VMAs spanning the memslot must be contiguous. */
+ if (!vma) {
+ ret = -EFAULT;
+ goto out;
+ }
+ /*
+ * VM_SHARED mappings are not allowed with MTE to avoid races
+ * when updating the PG_mte_tagged page flag, see
+ * sanitise_mte_tags for more details.
+ */
+ if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED) {
+ ret = -EFAULT;
+ goto out;
+ }
+ hva = min(slot_end, vma->vm_end);
+ } while (hva < slot_end);
+
+ /* ... then clear the tags. */
+ list_for_each_entry(entry, &memslot->arch.pages.list, list) {
+ page = entry->page;
+ if (!test_bit(PG_mte_tagged, &page->flags)) {
+ mte_clear_page_tags(page_address(page));
+ set_bit(PG_mte_tagged, &page->flags);
+ }
+ }
+
+out:
+ mmap_read_unlock(current->mm);
+
+ return ret;
+}
+
static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
struct kvm_memory_slot *memslot, unsigned long hva,
unsigned long fault_status)
@@ -1273,14 +1329,28 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
* - Stage 2 tables cannot be freed from under us as long as at least one VCPU
* is live, which means that the VM will be live.
*/
-void kvm_mmu_perform_pending_ops(struct kvm *kvm)
+int kvm_mmu_perform_pending_ops(struct kvm *kvm)
{
struct kvm_memory_slot *memslot;
+ int ret = 0;
mutex_lock(&kvm->slots_lock);
if (!kvm_mmu_has_pending_ops(kvm))
goto out_unlock;
+ if (test_bit(KVM_LOCKED_MEMSLOT_SANITISE_TAGS, &kvm->arch.mmu_pending_ops) &&
+ kvm_has_mte(kvm)) {
+ kvm_for_each_memslot(memslot, kvm_memslots(kvm)) {
+ if (!memslot_is_locked(memslot))
+ continue;
+ mmap_read_lock(current->mm);
+ ret = sanitise_mte_tags_memslot(kvm, memslot);
+ mmap_read_unlock(current->mm);
+ if (ret)
+ goto out_unlock;
+ }
+ }
+
if (test_bit(KVM_LOCKED_MEMSLOT_FLUSH_DCACHE, &kvm->arch.mmu_pending_ops)) {
kvm_for_each_memslot(memslot, kvm_memslots(kvm)) {
if (!memslot_is_locked(memslot))
@@ -1296,7 +1366,7 @@ void kvm_mmu_perform_pending_ops(struct kvm *kvm)
out_unlock:
mutex_unlock(&kvm->slots_lock);
- return;
+ return ret;
}
static int try_rlimit_memlock(unsigned long npages)
@@ -1390,19 +1460,6 @@ static int lock_memslot(struct kvm *kvm, struct kvm_memory_slot *memslot,
ret = -ENOMEM;
goto out_err;
}
- if (kvm_has_mte(kvm)) {
- if (vma->vm_flags & VM_SHARED) {
- ret = -EFAULT;
- } else {
- ret = sanitise_mte_tags(kvm,
- page_to_pfn(page_entry->page),
- PAGE_SIZE);
- }
- if (ret) {
- mmap_read_unlock(current->mm);
- goto out_err;
- }
- }
mmap_read_unlock(current->mm);
ret = kvm_mmu_topup_memory_cache(&cache, kvm_mmu_cache_min_pages(kvm));
@@ -1455,6 +1512,11 @@ static int lock_memslot(struct kvm *kvm, struct kvm_memory_slot *memslot,
memslot->arch.flags |= KVM_MEMSLOT_LOCK_WRITE;
set_bit(KVM_LOCKED_MEMSLOT_FLUSH_DCACHE, &kvm->arch.mmu_pending_ops);
+ /*
+ * MTE might be enabled after we lock the memslot, set it here
+ * unconditionally.
+ */
+ set_bit(KVM_LOCKED_MEMSLOT_SANITISE_TAGS, &kvm->arch.mmu_pending_ops);
kvm_mmu_free_memory_cache(&cache);
--
2.33.0
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