On Sat, Dec 17, 2022 at 09:54:31AM +0800, Baoquan He wrote:
> 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 will be skipped.
>
> Here, add a new function vb_vread() to read out areas managed by
> vmap_block specifically. Then recognize vm_map_ram areas via vmap->flags
> and handle them respectively.
>
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> ---
> mm/vmalloc.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 59 insertions(+), 7 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 190f29bbaaa7..6612914459cf 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3515,6 +3515,51 @@ static int aligned_vread(char *buf, char *addr, unsigned long count)
> return copied;
> }
>
> +static void vb_vread(char *buf, char *addr, int count)
> +{
> + char *start;
> + struct vmap_block *vb;
> + unsigned long offset;
> + unsigned int rs, re, n;
> +
> + 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);
> + if (addr < start) {
> + if (count == 0)
> + break;
> + *buf = '\0';
> + buf++;
> + addr++;
> + count--;
> + }
I may be missing something here, but is this not essentially 'if the address is
below a used region, write a single null byte into the buffer and continue,
assuming we are now in a used area?'
This doesn't seem right, but I am happy to be corrected (perhaps we only expect
to be a single byte below a start region?)
> + /*it could start reading from the middle of used region*/
> + offset = offset_in_page(addr);
> + n = (re - rs + 1) << PAGE_SHIFT - offset;
The kernel bot has already picked up on this paren issue :)
> + 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
> @@ -3545,7 +3590,7 @@ 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);
>
> @@ -3566,12 +3611,16 @@ 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;
>
This seems very delicate now as going forward, vm _could_ be NULL. In fact, a
later patch in the series then goes on to use vm and assume it is not null (will
comment).
I feel we should be very explicit after here asserting that vm != NULL.
> - vm = va->vm;
> - vaddr = (char *) vm->addr;
> - if (addr >= vaddr + get_vm_area_size(vm))
> + vaddr = (char *) va->va_start;
> + size = flags ? va_size(va) : get_vm_area_size(vm);
For example here, I feel that this ternary should be reversed and based on
whether vm is null, unles we expect vm to ever be non-null _and_ flags to be
set?
> +
> + if (addr >= vaddr + size)
> continue;
> while (addr < vaddr) {
> if (count == 0)
> @@ -3581,10 +3630,13 @@ 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_BLOCK)) == (VMAP_RAM|VMAP_BLOCK))
> + vb_vread(buf, addr, n);
> + else if ((flags & VMAP_RAM) || !(vm->flags & VM_IOREMAP))
> aligned_vread(buf, addr, n);
> else /* IOREMAP area is treated as memory hole */
> memset(buf, 0, n);
> --
> 2.34.1
>
