> With a machine with 3 TB (more than 2 TB memory). If you use vmalloc to
> allocate > 2 TB memory, the array_size below will be overflowed.

How was this observed?

Is there any know userspace operation which causes the kernel to try to
vmalloc such a large hunk of memory?

[Frank] The Dell PowerEdge R740/R940 can have up to  3TB/6TB memory.
installed. Our application requires reserve consecutive memory in the kernel
space and protected from userspace programs.

----------------------------------------------------------------------------------------------------
OK, thanks.  Against current mainline your proposed change would look
like this, yes?

[Frank] Yes. This will support up to less than 16 TB. If you want to support
 more than 16 TB, we need to expand nr_pages to unsigned long as
Matthew pointed out.

Will it be possible to add this to kernel 3.10.0-957.27.2.el7.x86_64?

Thanks,
Frank

On Tue, Nov 3, 2020 at 7:27 PM Andrew Morton <akpm@linux-foundation.org>
wrote:

> (switched to email.  Please respond via emailed reply-to-all, not via the
> bugzilla web interface).
>
> On Tue, 03 Nov 2020 18:50:07 +0000 bugzilla-daemon@bugzilla.kernel.org
> wrote:
>
> > https://bugzilla.kernel.org/show_bug.cgi?id=210023
> >
> >             Bug ID: 210023
> >            Summary: Crash when allocating > 2 TB memory
> >            Product: Memory Management
> >            Version: 2.5
> >     Kernel Version: 3.10.0-957.27.2.el7.x86_64
> >           Hardware: All
> >                 OS: Linux
> >               Tree: Mainline
> >             Status: NEW
> >           Severity: blocking
> >           Priority: P1
> >          Component: Slab Allocator
> >           Assignee: akpm@linux-foundation.org
> >           Reporter: hsinhuiwu@gmail.com
> >         Regression: No
> >
> > With a machine with 3 TB (more than 2 TB memory). If you use vmalloc to
> > allocate > 2 TB memory, the array_size below will be overflowed.
>
> How was this observed?
>
> Is there any know userspace operation which causes the kernel to try to
> vmalloc such a large hunk of memory?
>
> > The array_size is an unsigned int and can only be used to allocate less
> than 2
> > TB memory. If you pass 2*1028*1028*1024*1024 = 2 * 2^40 in the argument
> of
> > vmalloc. The array_size will become 2*2^31 = 2^32. The 2^32 cannot be
> store
> > with a 32 bit integer.
> >
> > The fix is to change the type of array_size to unsigned long.
> >
> > vmalloc.c
> >
> > 1762 void *vmalloc(unsigned long size)
> > 1763 {
> > 1764     return __vmalloc_node_flags(size, NUMA_NO_NODE,
> > 1765                     GFP_KERNEL | __GFP_HIGHMEM);
> > 1766 }
>
> OK, thanks.  Against current mainline your proposed change would look
> like this, yes?
>
> --- a/mm/vmalloc.c~a
> +++ a/mm/vmalloc.c
> @@ -2461,9 +2461,11 @@ static void *__vmalloc_area_node(struct
>  {
>         const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) |
> __GFP_ZERO;
>         unsigned int nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
> -       unsigned int array_size = nr_pages * sizeof(struct page *), i;
> +       unsigned long array_size
> +       unsigned int i;
>         struct page **pages;
>
> +       array_size = (unsigned long)nr_pages * sizeof(struct page *);
>         gfp_mask |= __GFP_NOWARN;
>         if (!(gfp_mask & (GFP_DMA | GFP_DMA32)))
>                 gfp_mask |= __GFP_HIGHMEM;
> _
>
>