kvm: x86, powerpc: do not allow clearing largepages debugfs entry

commit 833b45d upstream. The largepages debugfs entry is incremented/decremented as shadow pages are created or destroyed. Clearing it will result in an underflow, which is harmless to KVM but ugly (and could be misinterpreted by tools that use debugfs information), so make this particular statistic read-only. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: kvm-ppc@vger.kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
lhanjian · Nov 12, 2019 · a991063 · a991063
1 parent 580c79e
commit a991063
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Showing 3 changed files with 12 additions and 6 deletions.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
@@ -92,8 +92,8 @@ u64 __read_mostly efer_reserved_bits = ~((u64)(EFER_SCE | EFER_LME | EFER_LMA));
 static u64 __read_mostly efer_reserved_bits = ~((u64)EFER_SCE);
 #endif
 
-#define VM_STAT(x) offsetof(struct kvm, stat.x), KVM_STAT_VM
-#define VCPU_STAT(x) offsetof(struct kvm_vcpu, stat.x), KVM_STAT_VCPU
+#define VM_STAT(x, ...) offsetof(struct kvm, stat.x), KVM_STAT_VM, ## __VA_ARGS__
+#define VCPU_STAT(x, ...) offsetof(struct kvm_vcpu, stat.x), KVM_STAT_VCPU, ## __VA_ARGS__
 
 #define KVM_X2APIC_API_VALID_FLAGS (KVM_X2APIC_API_USE_32BIT_IDS | \
                                     KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK)
@@ -205,7 +205,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 	{ "mmu_cache_miss", VM_STAT(mmu_cache_miss) },
 	{ "mmu_unsync", VM_STAT(mmu_unsync) },
 	{ "remote_tlb_flush", VM_STAT(remote_tlb_flush) },
-	{ "largepages", VM_STAT(lpages) },
+	{ "largepages", VM_STAT(lpages, .mode = 0444) },
 	{ "max_mmu_page_hash_collisions",
 		VM_STAT(max_mmu_page_hash_collisions) },
 	{ NULL }

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
@@ -1034,13 +1034,15 @@ enum kvm_stat_kind {
 
 struct kvm_stat_data {
 	int offset;
+	int mode;
 	struct kvm *kvm;
 };
 
 struct kvm_stats_debugfs_item {
 	const char *name;
 	int offset;
 	enum kvm_stat_kind kind;
+	int mode;
 };
 extern struct kvm_stats_debugfs_item debugfs_entries[];
 extern struct dentry *kvm_debugfs_dir;

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -616,8 +616,9 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
 
 		stat_data->kvm = kvm;
 		stat_data->offset = p->offset;
+		stat_data->mode = p->mode ? p->mode : 0644;
 		kvm->debugfs_stat_data[p - debugfs_entries] = stat_data;
-		debugfs_create_file(p->name, 0644, kvm->debugfs_dentry,
+		debugfs_create_file(p->name, stat_data->mode, kvm->debugfs_dentry,
 				    stat_data, stat_fops_per_vm[p->kind]);
 	}
 	return 0;
@@ -3714,7 +3715,9 @@ static int kvm_debugfs_open(struct inode *inode, struct file *file,
 	if (!refcount_inc_not_zero(&stat_data->kvm->users_count))
 		return -ENOENT;
 
-	if (simple_attr_open(inode, file, get, set, fmt)) {
+	if (simple_attr_open(inode, file, get,
+			     stat_data->mode & S_IWUGO ? set : NULL,
+			     fmt)) {
 		kvm_put_kvm(stat_data->kvm);
 		return -ENOMEM;
 	}
@@ -3962,7 +3965,8 @@ static void kvm_init_debug(void)
 
 	kvm_debugfs_num_entries = 0;
 	for (p = debugfs_entries; p->name; ++p, kvm_debugfs_num_entries++) {
-		debugfs_create_file(p->name, 0644, kvm_debugfs_dir,
+		int mode = p->mode ? p->mode : 0644;
+		debugfs_create_file(p->name, mode, kvm_debugfs_dir,
 				    (void *)(long)p->offset,
 				    stat_fops[p->kind]);
 	}