[PATCH v3 3/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas

Baoquan He
2023-01-13T03:21:00Z

Currently, vread can read out vmalloc areas which is associated with
a vm_struct. While this doesn't work for areas created by vm_map_ram()
interface because it doesn't have an associated vm_struct. Then in vread(),
these areas are all skipped.

Here, add a new function vmap_ram_vread() to read out vm_map_ram areas.
The area created with vmap_ram_vread() interface directly can be handled
like the other normal vmap areas with aligned_vread(). While areas
which will be further subdivided and managed with vmap_block need
carefully read out page-aligned small regions and zero fill holes.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
mm/vmalloc.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 73 insertions(+), 7 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ab4825050b5c..13875bc41e27 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3544,6 +3544,65 @@ static int aligned_vread(char *buf, char *addr, unsigned long count)
return copied;
}

+static void vmap_ram_vread(char *buf, char *addr, int count, unsigned long flags)
+{
+ char *start;
+ struct vmap_block *vb;
+ unsigned long offset;
+ unsigned int rs, re, n;
+
+ /*
+ * If it's area created by vm_map_ram() interface directly, but
+ * not further subdividing and delegating management to vmap_block,
+ * handle it here.
+ */
+ if (!(flags & VMAP_BLOCK)) {
+ aligned_vread(buf, addr, count);
+ return;
+ }
+
+ /*
+ * Area is split into regions and tracked with vmap_block, read out
+ * each region and zero fill the hole between regions.
+ */
+ vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
+
+ spin_lock(&vb->lock);
+ if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
+ spin_unlock(&vb->lock);
+ memset(buf, 0, count);
+ return;
+ }
+ for_each_set_bitrange(rs, re, vb->used_map, VMAP_BBMAP_BITS) {
+ if (!count)
+ break;
+ start = vmap_block_vaddr(vb->va->va_start, rs);
+ while (addr < start) {
+ if (count == 0)
+ break;
+ *buf = '\0';
+ buf++;
+ addr++;
+ count--;
+ }
+ /*it could start reading from the middle of used region*/
+ offset = offset_in_page(addr);
+ n = ((re - rs + 1) << PAGE_SHIFT) - offset;
+ if (n > count)
+ n = count;
+ aligned_vread(buf, start+offset, n);
+
+ buf += n;
+ addr += n;
+ count -= n;
+ }
+ spin_unlock(&vb->lock);
+
+ /* zero-fill the left dirty or free regions */
+ if (count)
+ memset(buf, 0, count);
+}
+
/**
* vread() - read vmalloc area in a safe way.
* @buf: buffer for reading data
@@ -3574,7 +3633,7 @@ long vread(char *buf, char *addr, unsigned long count)
struct vm_struct *vm;
char *vaddr, *buf_start = buf;
unsigned long buflen = count;
- unsigned long n;
+ unsigned long n, size, flags;

addr = kasan_reset_tag(addr);

@@ -3595,12 +3654,16 @@ long vread(char *buf, char *addr, unsigned long count)
if (!count)
break;

- if (!va->vm)
+ vm = va->vm;
+ flags = va->flags & VMAP_FLAGS_MASK;
+
+ if (!vm && !flags)
continue;

- vm = va->vm;
- vaddr = (char *) vm->addr;
- if (addr >= vaddr + get_vm_area_size(vm))
+ vaddr = (char *) va->va_start;
+ size = vm ? get_vm_area_size(vm) : va_size(va);
+
+ if (addr >= vaddr + size)
continue;
while (addr < vaddr) {
if (count == 0)
@@ -3610,10 +3673,13 @@ long vread(char *buf, char *addr, unsigned long count)
addr++;
count--;
}
- n = vaddr + get_vm_area_size(vm) - addr;
+ n = vaddr + size - addr;
if (n > count)
n = count;
- if (!(vm->flags & VM_IOREMAP))
+
+ if (flags & VMAP_RAM)
+ vmap_ram_vread(buf, addr, n, flags);
+ else if (!(vm->flags & VM_IOREMAP))
aligned_vread(buf, addr, n);
else /* IOREMAP area is treated as memory hole */
memset(buf, 0, n);
--
2.34.1