mm: vmalloc: support multiple nodes in vread_iter

Extend the vread_iter() to be able to perform a sequential reading of VAs
which are spread among multiple nodes.  So a data read over the /dev/kmem
correctly reflects a vmalloc memory layout.

Link: https://lkml.kernel.org/r/20240102184633.748113-9-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Kazuhito Hagio <k-hagio-ab@nec.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 75e96cf377ef3473f1301f6c12349458d7e9683e..5a2db5b66333b951175943e71a3f36daa5dc21f8 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -906,7 +906,7 @@ unsigned long vmalloc_nr_pages(void)
 
 /* Look up the first VA which satisfies addr < va_end, NULL if none. */
 static struct vmap_area *
-find_vmap_area_exceed_addr(unsigned long addr, struct rb_root *root)
+__find_vmap_area_exceed_addr(unsigned long addr, struct rb_root *root)
 {
        struct vmap_area *va = NULL;
        struct rb_node *n = root->rb_node;
@@ -930,6 +930,41 @@ find_vmap_area_exceed_addr(unsigned long addr, struct rb_root *root)
        return va;
 }
 
+/*
+ * Returns a node where a first VA, that satisfies addr < va_end, resides.
+ * If success, a node is locked. A user is responsible to unlock it when a
+ * VA is no longer needed to be accessed.
+ *
+ * Returns NULL if nothing found.
+ */
+static struct vmap_node *
+find_vmap_area_exceed_addr_lock(unsigned long addr, struct vmap_area **va)
+{
+       struct vmap_node *vn, *va_node = NULL;
+       struct vmap_area *va_lowest;
+       int i;
+
+       for (i = 0; i < nr_vmap_nodes; i++) {
+               vn = &vmap_nodes[i];
+
+               spin_lock(&vn->busy.lock);
+               va_lowest = __find_vmap_area_exceed_addr(addr, &vn->busy.root);
+               if (va_lowest) {
+                       if (!va_node || va_lowest->va_start < (*va)->va_start) {
+                               if (va_node)
+                                       spin_unlock(&va_node->busy.lock);
+
+                               *va = va_lowest;
+                               va_node = vn;
+                               continue;
+                       }
+               }
+               spin_unlock(&vn->busy.lock);
+       }
+
+       return va_node;
+}
+
 static struct vmap_area *__find_vmap_area(unsigned long addr, struct rb_root *root)
 {
        struct rb_node *n = root->rb_node;
@@ -4102,6 +4137,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
        struct vm_struct *vm;
        char *vaddr;
        size_t n, size, flags, remains;
+       unsigned long next;
 
        addr = kasan_reset_tag(addr);
 
@@ -4111,19 +4147,15 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
 
        remains = count;
 
-       /* Hooked to node_0 so far. */
-       vn = addr_to_node(0);
-       spin_lock(&vn->busy.lock);
-
-       va = find_vmap_area_exceed_addr((unsigned long)addr, &vn->busy.root);
-       if (!va)
+       vn = find_vmap_area_exceed_addr_lock((unsigned long) addr, &va);
+       if (!vn)
                goto finished_zero;
 
        /* no intersects with alive vmap_area */
        if ((unsigned long)addr + remains <= va->va_start)
                goto finished_zero;
 
-       list_for_each_entry_from(va, &vn->busy.head, list) {
+       do {
                size_t copied;
 
                if (remains == 0)
@@ -4138,10 +4170,10 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
                WARN_ON(flags == VMAP_BLOCK);
 
                if (!vm && !flags)
-                       continue;
+                       goto next_va;
 
                if (vm && (vm->flags & VM_UNINITIALIZED))
-                       continue;
+                       goto next_va;
 
                /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
                smp_rmb();
@@ -4150,7 +4182,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
                size = vm ? get_vm_area_size(vm) : va_size(va);
 
                if (addr >= vaddr + size)
-                       continue;
+                       goto next_va;
 
                if (addr < vaddr) {
                        size_t to_zero = min_t(size_t, vaddr - addr, remains);
@@ -4179,15 +4211,22 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
 
                if (copied != n)
                        goto finished;
-       }
+
+       next_va:
+               next = va->va_end;
+               spin_unlock(&vn->busy.lock);
+       } while ((vn = find_vmap_area_exceed_addr_lock(next, &va)));
 
 finished_zero:
-       spin_unlock(&vn->busy.lock);
+       if (vn)
+               spin_unlock(&vn->busy.lock);
+
        /* zero-fill memory holes */
        return count - remains + zero_iter(iter, remains);
 finished:
        /* Nothing remains, or We couldn't copy/zero everything. */
-       spin_unlock(&vn->busy.lock);
+       if (vn)
+               spin_unlock(&vn->busy.lock);
 
        return count - remains;
 }