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    Subject[PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM


    On Wed, 18 Apr 2018, Mikulas Patocka wrote:

    >
    >
    > On Wed, 18 Apr 2018, David Miller wrote:
    >
    > > From: Mikulas Patocka <mpatocka@redhat.com>
    > > Date: Wed, 18 Apr 2018 12:44:25 -0400 (EDT)
    > >
    > > > The structure net_device is followed by arbitrary driver-specific data
    > > > (accessible with the function netdev_priv). And for virtio-net, these
    > > > driver-specific data must be in DMA memory.
    > >
    > > And we are saying that this assumption is wrong and needs to be
    > > corrected.
    >
    > So, try to find all the networking drivers that to DMA to the private
    > area.
    >
    > The problem here is that kvzalloc usually returns DMA-able area, but it
    > may return non-DMA area rarely, if the memory is too fragmented. So, we
    > are in a situation, where some networking drivers will randomly fail. Go
    > and find them.
    >
    > Mikulas

    Her I submit a patch that makes kvmalloc always use vmalloc if
    CONFIG_DEBUG_VM is defined.




    From: Mikulas Patocka <mpatocka@redhat.com>
    Subject: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM

    The kvmalloc function tries to use kmalloc and falls back to vmalloc if
    kmalloc fails.

    Unfortunatelly, some kernel code has bugs - it uses kvmalloc and then
    uses DMA-API on the returned memory or frees it with kfree. Such bugs were
    found in the virtio-net driver, dm-integrity or RHEL7 powerpc-specific
    code.

    These bugs are hard to reproduce because vmalloc falls back to kmalloc
    only if memory is fragmented.

    In order to detect these bugs reliably I submit this patch that changes
    kvmalloc to always use vmalloc if CONFIG_DEBUG_VM is turned on.

    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

    ---
    mm/util.c | 2 ++
    1 file changed, 2 insertions(+)

    Index: linux-2.6/mm/util.c
    ===================================================================
    --- linux-2.6.orig/mm/util.c 2018-04-18 15:46:23.000000000 +0200
    +++ linux-2.6/mm/util.c 2018-04-18 16:00:43.000000000 +0200
    @@ -395,6 +395,7 @@ EXPORT_SYMBOL(vm_mmap);
    */
    void *kvmalloc_node(size_t size, gfp_t flags, int node)
    {
    +#ifndef CONFIG_DEBUG_VM
    gfp_t kmalloc_flags = flags;
    void *ret;

    @@ -426,6 +427,7 @@ void *kvmalloc_node(size_t size, gfp_t f
    */
    if (ret || size <= PAGE_SIZE)
    return ret;
    +#endif

    return __vmalloc_node_flags_caller(size, node, flags,
    __builtin_return_address(0));
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