Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

From: Ackerley Tng
Date: Tue Mar 07 2023 - 14:28:29 EST

Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> writes:

Register/unregister private memslot to fd-based memory backing store
restrictedmem and implement the callbacks for restrictedmem_notifier:
- invalidate_start()/invalidate_end() to zap the existing memory
mappings in the KVM page table.
- error() to request KVM_REQ_MEMORY_MCE and later exit to userspace
with KVM_EXIT_SHUTDOWN.

Expose KVM_MEM_PRIVATE for memslot and KVM_MEMORY_ATTRIBUTE_PRIVATE for
KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to userspace but either are
controlled by kvm_arch_has_private_mem() which should be rewritten by
architecture code.

Could we perhaps rename KVM_MEM_PRIVATE to KVM_MEM_PROTECTED, to be in
line with KVM_X86_PROTECTED_VM?

I feel that a memslot that has the KVM_MEM_PRIVATE flag need not always
be private; It can sometimes be providing memory that is shared and
also accessible from the host.

KVM_MEMORY_ATTRIBUTE_PRIVATE is fine as-is because this flag is set when
the guest memory is meant to be backed by private memory.

KVM_MEMORY_EXIT_FLAG_PRIVATE is also okay because the flag is used to
indicate when the memory error is caused by a private access (as opposed
to a shared access).

kvm_slot_can_be_private() could perhaps be renamed kvm_is_protected_slot()?


Co-developed-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/x86.c | 13 +++
include/linux/kvm_host.h | 3 +
virt/kvm/kvm_main.c | 179 +++++++++++++++++++++++++++++++-
4 files changed, 191 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7772ab37ac89..27ef31133352 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -114,6 +114,7 @@
KVM_ARCH_REQ_FLAGS(31, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
#define KVM_REQ_HV_TLB_FLUSH \
KVM_ARCH_REQ_FLAGS(32, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_MEMORY_MCE KVM_ARCH_REQ(33)

#define CR0_RESERVED_BITS \
(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5aefcff614d2..c67e22f3e2ee 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6587,6 +6587,13 @@ int kvm_arch_pm_notifier(struct kvm *kvm, unsigned long state)
}
#endif /* CONFIG_HAVE_KVM_PM_NOTIFIER */

+#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
+void kvm_arch_memory_mce(struct kvm *kvm)
+{
+ kvm_make_all_cpus_request(kvm, KVM_REQ_MEMORY_MCE);
+}
+#endif
+
static int kvm_vm_ioctl_get_clock(struct kvm *kvm, void __user *argp)
{
struct kvm_clock_data data = { 0 };
@@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)

if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
+
+ if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
+ vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
+ r = 0;
+ goto out;
+ }
}

if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win ||
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 153842bb33df..f032d878e034 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -590,6 +590,7 @@ struct kvm_memory_slot {
struct file *restricted_file;
loff_t restricted_offset;
struct restrictedmem_notifier notifier;
+ struct kvm *kvm;
};

static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
@@ -2363,6 +2364,8 @@ static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
*pfn = page_to_pfn(page);
return ret;
}
+
+void kvm_arch_memory_mce(struct kvm *kvm);
#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */

#endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e107afea32f0..ac835fc77273 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -936,6 +936,121 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)

#endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */

+#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
+static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot,
+ pgoff_t start, pgoff_t end,
+ gfn_t *gfn_start, gfn_t *gfn_end)
+{
+ unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT;
+
+ if (start > base_pgoff)
+ *gfn_start = slot->base_gfn + start - base_pgoff;
+ else
+ *gfn_start = slot->base_gfn;
+
+ if (end < base_pgoff + slot->npages)
+ *gfn_end = slot->base_gfn + end - base_pgoff;
+ else
+ *gfn_end = slot->base_gfn + slot->npages;
+
+ if (*gfn_start >= *gfn_end)
+ return false;
+
+ return true;
+}
+
+static void kvm_restrictedmem_invalidate_begin(struct restrictedmem_notifier *notifier,
+ pgoff_t start, pgoff_t end)
+{
+ struct kvm_memory_slot *slot = container_of(notifier,
+ struct kvm_memory_slot,
+ notifier);
+ struct kvm *kvm = slot->kvm;
+ gfn_t gfn_start, gfn_end;
+ struct kvm_gfn_range gfn_range;
+ int idx;
+
+ if (!restrictedmem_range_is_valid(slot, start, end,
+ &gfn_start, &gfn_end))
+ return;
+
+ gfn_range.start = gfn_start;
+ gfn_range.end = gfn_end;
+ gfn_range.slot = slot;
+ gfn_range.pte = __pte(0);
+ gfn_range.may_block = true;
+
+ idx = srcu_read_lock(&kvm->srcu);
+ KVM_MMU_LOCK(kvm);
+
+ kvm_mmu_invalidate_begin(kvm);
+ kvm_mmu_invalidate_range_add(kvm, gfn_start, gfn_end);
+ if (kvm_unmap_gfn_range(kvm, &gfn_range))
+ kvm_flush_remote_tlbs(kvm);
+
+ KVM_MMU_UNLOCK(kvm);
+ srcu_read_unlock(&kvm->srcu, idx);
+}
+
+static void kvm_restrictedmem_invalidate_end(struct restrictedmem_notifier *notifier,
+ pgoff_t start, pgoff_t end)
+{
+ struct kvm_memory_slot *slot = container_of(notifier,
+ struct kvm_memory_slot,
+ notifier);
+ struct kvm *kvm = slot->kvm;
+ gfn_t gfn_start, gfn_end;
+
+ if (!restrictedmem_range_is_valid(slot, start, end,
+ &gfn_start, &gfn_end))
+ return;
+
+ KVM_MMU_LOCK(kvm);
+ kvm_mmu_invalidate_end(kvm);
+ KVM_MMU_UNLOCK(kvm);
+}
+
+static void kvm_restrictedmem_error(struct restrictedmem_notifier *notifier,
+ pgoff_t start, pgoff_t end)
+{
+ struct kvm_memory_slot *slot = container_of(notifier,
+ struct kvm_memory_slot,
+ notifier);
+ kvm_arch_memory_mce(slot->kvm);
+}
+
+static struct restrictedmem_notifier_ops kvm_restrictedmem_notifier_ops = {
+ .invalidate_start = kvm_restrictedmem_invalidate_begin,
+ .invalidate_end = kvm_restrictedmem_invalidate_end,
+ .error = kvm_restrictedmem_error,
+};
+
+static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)
+{
+ slot->notifier.ops = &kvm_restrictedmem_notifier_ops;
+ restrictedmem_register_notifier(slot->restricted_file, &slot->notifier);
+}
+
+static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
+{
+ restrictedmem_unregister_notifier(slot->restricted_file,
+ &slot->notifier);
+}
+
+#else /* !CONFIG_HAVE_KVM_RESTRICTED_MEM */
+
+static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)
+{
+ WARN_ON_ONCE(1);
+}
+
+static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
+{
+ WARN_ON_ONCE(1);
+}
+
+#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
+
#ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
static int kvm_pm_notifier_call(struct notifier_block *bl,
unsigned long state,
@@ -980,6 +1095,11 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
/* This does not remove the slot from struct kvm_memslots data structures */
static void kvm_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
{
+ if (slot->flags & KVM_MEM_PRIVATE) {
+ kvm_restrictedmem_unregister(slot);
+ fput(slot->restricted_file);
+ }
+
kvm_destroy_dirty_bitmap(slot);

kvm_arch_free_memslot(kvm, slot);
@@ -1551,10 +1671,14 @@ static void kvm_replace_memslot(struct kvm *kvm,
}
}

-static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
+static int check_memory_region_flags(struct kvm *kvm,
+ const struct kvm_user_mem_region *mem)
{
u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;

+ if (kvm_arch_has_private_mem(kvm))
+ valid_flags |= KVM_MEM_PRIVATE;
+
#ifdef __KVM_HAVE_READONLY_MEM
valid_flags |= KVM_MEM_READONLY;
#endif
@@ -1630,6 +1754,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
{
int r;

+ if (change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
+ kvm_restrictedmem_register(new);
+
/*
* If dirty logging is disabled, nullify the bitmap; the old bitmap
* will be freed on "commit". If logging is enabled in both old and
@@ -1658,6 +1785,9 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
if (r && new && new->dirty_bitmap && (!old || !old->dirty_bitmap))
kvm_destroy_dirty_bitmap(new);

+ if (r && change == KVM_MR_CREATE && new->flags & KVM_MEM_PRIVATE)
+ kvm_restrictedmem_unregister(new);
+
return r;
}

@@ -1963,7 +2093,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
int as_id, id;
int r;

- r = check_memory_region_flags(mem);
+ r = check_memory_region_flags(kvm, mem);
if (r)
return r;

@@ -1982,6 +2112,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
!access_ok((void __user *)(unsigned long)mem->userspace_addr,
mem->memory_size))
return -EINVAL;
+ if (mem->flags & KVM_MEM_PRIVATE &&
+ (mem->restricted_offset & (PAGE_SIZE - 1) ||
+ mem->restricted_offset > U64_MAX - mem->memory_size))
+ return -EINVAL;
if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
return -EINVAL;
if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
@@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
return -EINVAL;
} else { /* Modify an existing slot. */
+ /* Private memslots are immutable, they can only be deleted. */
+ if (mem->flags & KVM_MEM_PRIVATE)
+ return -EINVAL;
if ((mem->userspace_addr != old->userspace_addr) ||
(npages != old->npages) ||
((mem->flags ^ old->flags) & KVM_MEM_READONLY))
@@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
new->npages = npages;
new->flags = mem->flags;
new->userspace_addr = mem->userspace_addr;
+ if (mem->flags & KVM_MEM_PRIVATE) {
+ new->restricted_file = fget(mem->restricted_fd);
+ if (!new->restricted_file ||
+ !file_is_restrictedmem(new->restricted_file)) {
+ r = -EINVAL;
+ goto out;
+ }
+ new->restricted_offset = mem->restricted_offset;
+ }
+
+ new->kvm = kvm;

r = kvm_set_memslot(kvm, old, new, change);
if (r)
- kfree(new);
+ goto out;
+
+ return 0;
+
+out:
+ if (new->restricted_file)
+ fput(new->restricted_file);
+ kfree(new);
return r;
}
EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
@@ -2351,6 +2506,8 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
static u64 kvm_supported_mem_attributes(struct kvm *kvm)
{
+ if (kvm_arch_has_private_mem(kvm))
+ return KVM_MEMORY_ATTRIBUTE_PRIVATE;
return 0;
}

@@ -4822,16 +4979,28 @@ static long kvm_vm_ioctl(struct file *filp,
}
case KVM_SET_USER_MEMORY_REGION: {
struct kvm_user_mem_region mem;
- unsigned long size = sizeof(struct kvm_userspace_memory_region);
+ unsigned int flags_offset = offsetof(typeof(mem), flags);
+ unsigned long size;
+ u32 flags;

kvm_sanity_check_user_mem_region_alias();

+ memset(&mem, 0, sizeof(mem));
+
r = -EFAULT;
+ if (get_user(flags, (u32 __user *)(argp + flags_offset)))
+ goto out;
+
+ if (flags & KVM_MEM_PRIVATE)
+ size = sizeof(struct kvm_userspace_memory_region_ext);
+ else
+ size = sizeof(struct kvm_userspace_memory_region);
+
if (copy_from_user(&mem, argp, size))
goto out;

r = -EINVAL;
- if (mem.flags & KVM_MEM_PRIVATE)
+ if ((flags ^ mem.flags) & KVM_MEM_PRIVATE)
goto out;

r = kvm_vm_ioctl_set_memory_region(kvm, &mem);