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SubjectRe: [PATCH bpf-next v2 2/3] xdp: xdp_umem: replace kmap on vmap for umem map
Date
On 15 Aug 2019, at 5:13, Ivan Khoronzhuk wrote:

> For 64-bit there is no reason to use vmap/vunmap, so use page_address
> as it was initially. For 32 bits, in some apps, like in samples
> xdpsock_user.c when number of pgs in use is quite big, the kmap
> memory can be not enough, despite on this, kmap looks like is
> deprecated in such cases as it can block and should be used rather
> for dynamic mm.
>
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
> ---
> net/xdp/xdp_umem.c | 36 ++++++++++++++++++++++++++++++------
> 1 file changed, 30 insertions(+), 6 deletions(-)
>
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> index a0607969f8c0..d740c4f8810c 100644
> --- a/net/xdp/xdp_umem.c
> +++ b/net/xdp/xdp_umem.c
> @@ -14,7 +14,7 @@
> #include <linux/netdevice.h>
> #include <linux/rtnetlink.h>
> #include <linux/idr.h>
> -#include <linux/highmem.h>
> +#include <linux/vmalloc.h>
>
> #include "xdp_umem.h"
> #include "xsk_queue.h"
> @@ -170,7 +170,30 @@ static void xdp_umem_unmap_pages(struct xdp_umem
> *umem)
> unsigned int i;
>
> for (i = 0; i < umem->npgs; i++)
> - kunmap(umem->pgs[i]);
> + if (PageHighMem(umem->pgs[i]))
> + vunmap(umem->pages[i].addr);
> +}
> +
> +static int xdp_umem_map_pages(struct xdp_umem *umem)
> +{
> + unsigned int i;
> + void *addr;
> +
> + for (i = 0; i < umem->npgs; i++) {
> + if (PageHighMem(umem->pgs[i]))
> + addr = vmap(&umem->pgs[i], 1, VM_MAP, PAGE_KERNEL);
> + else
> + addr = page_address(umem->pgs[i]);
> +
> + if (!addr) {
> + xdp_umem_unmap_pages(umem);
> + return -ENOMEM;
> + }
> +
> + umem->pages[i].addr = addr;
> + }
> +
> + return 0;
> }

You'll want a __xdp_umem_unmap_pages() helper here that takes an
count of the number of pages to unmap, so it can be called from
xdp_umem_unmap_pages() in the normal case, and xdp_umem_map_pages()
in the error case. Otherwise the error case ends up calling
PageHighMem on a null page.
--
Jonathan

> static void xdp_umem_unpin_pages(struct xdp_umem *umem)
> @@ -312,7 +335,7 @@ static int xdp_umem_reg(struct xdp_umem *umem,
> struct xdp_umem_reg *mr)
> u32 chunk_size = mr->chunk_size, headroom = mr->headroom;
> unsigned int chunks, chunks_per_page;
> u64 addr = mr->addr, size = mr->len;
> - int size_chk, err, i;
> + int size_chk, err;
>
> if (chunk_size < XDP_UMEM_MIN_CHUNK_SIZE || chunk_size > PAGE_SIZE)
> {
> /* Strictly speaking we could support this, if:
> @@ -378,10 +401,11 @@ static int xdp_umem_reg(struct xdp_umem *umem,
> struct xdp_umem_reg *mr)
> goto out_account;
> }
>
> - for (i = 0; i < umem->npgs; i++)
> - umem->pages[i].addr = kmap(umem->pgs[i]);
> + err = xdp_umem_map_pages(umem);
> + if (!err)
> + return 0;
>
> - return 0;
> + kfree(umem->pages);
>
> out_account:
> xdp_umem_unaccount_pages(umem);
> --
> 2.17.1

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