FreeBSD/Linux Kernel Cross Reference
sys/net/bpf_zerocopy.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2007 Seccuris Inc.
      * All rights reserved.
      *
      * This software was developed by Robert N. M. Watson under contract to
      * Seccuris Inc.
      *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_bpf.h"
    
    #include <sys/param.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mbuf.h>
    #include <sys/mutex.h>
    #include <sys/proc.h>
    #include <sys/sf_buf.h>
    #include <sys/socket.h>
    #include <sys/uio.h>
    
    #include <machine/atomic.h>
    
    #include <net/if.h>
    #include <net/bpf.h>
    #include <net/bpf_zerocopy.h>
    #include <net/bpfdesc.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/pmap.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_map.h>
    #include <vm/vm_page.h>
    
    /*
     * Zero-copy buffer scheme for BPF: user space "donates" two buffers, which
     * are mapped into the kernel address space using sf_bufs and used directly
     * by BPF.  Memory is wired since page faults cannot be tolerated in the
     * contexts where the buffers are copied to (locks held, interrupt context,
     * etc).  Access to shared memory buffers is synchronized using a header on
     * each buffer, allowing the number of system calls to go to zero as BPF
     * reaches saturation (buffers filled as fast as they can be drained by the
     * user process).  Full details of the protocol for communicating between the
     * user process and BPF may be found in bpf(4).
     */
    
    /*
     * Maximum number of pages per buffer.  Since all BPF devices use two, the
     * maximum per device is 2*BPF_MAX_PAGES.  Resource limits on the number of
     * sf_bufs may be an issue, so do not set this too high.  On older systems,
     * kernel address space limits may also be an issue.
     */
    #define BPF_MAX_PAGES   512
    
    /*
     * struct zbuf describes a memory buffer loaned by a user process to the
     * kernel.  We represent this as a series of pages managed using an array of
     * sf_bufs.  Even though the memory is contiguous in user space, it may not
     * be mapped contiguously in the kernel (i.e., a set of physically
     * non-contiguous pages in the direct map region) so we must implement
     * scatter-gather copying.  One significant mitigating factor is that on
     * systems with a direct memory map, we can avoid TLB misses.
     *
     * At the front of the shared memory region is a bpf_zbuf_header, which
     * contains shared control data to allow user space and the kernel to
     * synchronize; this is included in zb_size, but not bpf_bufsize, so that BPF
     * knows that the space is not available.
     */
    struct zbuf {
            vm_offset_t      zb_uaddr;      /* User address at time of setup. */
            size_t           zb_size;       /* Size of buffer, incl. header. */
            u_int            zb_numpages;   /* Number of pages. */
            int              zb_flags;      /* Flags on zbuf. */
           struct sf_buf   **zb_pages;     /* Pages themselves. */
           struct bpf_zbuf_header  *zb_header;     /* Shared header. */
   };
   
   /*
    * When a buffer has been assigned to userspace, flag it as such, as the
    * buffer may remain in the store position as a result of the user process
    * not yet having acknowledged the buffer in the hold position yet.
    */
   #define ZBUF_FLAG_ASSIGNED      0x00000001      /* Set when owned by user. */
   
   /*
    * Release a page we've previously wired.
    */
   static void
   zbuf_page_free(vm_page_t pp)
   {
   
           vm_page_unwire(pp, PQ_INACTIVE);
   }
   
   /*
    * Free an sf_buf with attached page.
    */
   static void
   zbuf_sfbuf_free(struct sf_buf *sf)
   {
           vm_page_t pp;
   
           pp = sf_buf_page(sf);
           sf_buf_free(sf);
           zbuf_page_free(pp);
   }
   
   /*
    * Free a zbuf, including its page array, sbufs, and pages.  Allow partially
    * allocated zbufs to be freed so that it may be used even during a zbuf
    * setup.
    */
   static void
   zbuf_free(struct zbuf *zb)
   {
           int i;
   
           for (i = 0; i < zb->zb_numpages; i++) {
                   if (zb->zb_pages[i] != NULL)
                           zbuf_sfbuf_free(zb->zb_pages[i]);
           }
           free(zb->zb_pages, M_BPF);
           free(zb, M_BPF);
   }
   
   /*
    * Given a user pointer to a page of user memory, return an sf_buf for the
    * page.  Because we may be requesting quite a few sf_bufs, prefer failure to
    * deadlock and use SFB_NOWAIT.
    */
   static struct sf_buf *
   zbuf_sfbuf_get(struct vm_map *map, vm_offset_t uaddr)
   {
           struct sf_buf *sf;
           vm_page_t pp;
   
           if (vm_fault_quick_hold_pages(map, uaddr, PAGE_SIZE, VM_PROT_READ |
               VM_PROT_WRITE, &pp, 1) < 0)
                   return (NULL);
           sf = sf_buf_alloc(pp, SFB_NOWAIT);
           if (sf == NULL) {
                   zbuf_page_free(pp);
                   return (NULL);
           }
           return (sf);
   }
   
   /*
    * Create a zbuf describing a range of user address space memory.  Validate
    * page alignment, size requirements, etc.
    */
   static int
   zbuf_setup(struct thread *td, vm_offset_t uaddr, size_t len,
       struct zbuf **zbp)
   {
           struct zbuf *zb;
           struct vm_map *map;
           int error, i;
   
           *zbp = NULL;
   
           /*
            * User address must be page-aligned.
            */
           if (uaddr & PAGE_MASK)
                   return (EINVAL);
   
           /*
            * Length must be an integer number of full pages.
            */
           if (len & PAGE_MASK)
                   return (EINVAL);
   
           /*
            * Length must not exceed per-buffer resource limit.
            */
           if ((len / PAGE_SIZE) > BPF_MAX_PAGES)
                   return (EINVAL);
   
           /*
            * Allocate the buffer and set up each page with is own sf_buf.
            */
           error = 0;
           zb = malloc(sizeof(*zb), M_BPF, M_ZERO | M_WAITOK);
           zb->zb_uaddr = uaddr;
           zb->zb_size = len;
           zb->zb_numpages = len / PAGE_SIZE;
           zb->zb_pages = malloc(sizeof(struct sf_buf *) *
               zb->zb_numpages, M_BPF, M_ZERO | M_WAITOK);
           map = &td->td_proc->p_vmspace->vm_map;
           for (i = 0; i < zb->zb_numpages; i++) {
                   zb->zb_pages[i] = zbuf_sfbuf_get(map,
                       uaddr + (i * PAGE_SIZE));
                   if (zb->zb_pages[i] == NULL) {
                           error = EFAULT;
                           goto error;
                   }
           }
           zb->zb_header =
               (struct bpf_zbuf_header *)sf_buf_kva(zb->zb_pages[0]);
           bzero(zb->zb_header, sizeof(*zb->zb_header));
           *zbp = zb;
           return (0);
   
   error:
           zbuf_free(zb);
           return (error);
   }
   
   /*
    * Copy bytes from a source into the specified zbuf.  The caller is
    * responsible for performing bounds checking, etc.
    */
   void
   bpf_zerocopy_append_bytes(struct bpf_d *d, caddr_t buf, u_int offset,
       void *src, u_int len)
   {
           u_int count, page, poffset;
           u_char *src_bytes;
           struct zbuf *zb;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_append_bytes: not in zbuf mode"));
           KASSERT(buf != NULL, ("bpf_zerocopy_append_bytes: NULL buf"));
   
           src_bytes = (u_char *)src;
           zb = (struct zbuf *)buf;
   
           KASSERT((zb->zb_flags & ZBUF_FLAG_ASSIGNED) == 0,
               ("bpf_zerocopy_append_bytes: ZBUF_FLAG_ASSIGNED"));
   
           /*
            * Scatter-gather copy to user pages mapped into kernel address space
            * using sf_bufs: copy up to a page at a time.
            */
           offset += sizeof(struct bpf_zbuf_header);
           page = offset / PAGE_SIZE;
           poffset = offset % PAGE_SIZE;
           while (len > 0) {
                   KASSERT(page < zb->zb_numpages, ("bpf_zerocopy_append_bytes:"
                      " page overflow (%d p %d np)\n", page, zb->zb_numpages));
   
                   count = min(len, PAGE_SIZE - poffset);
                   bcopy(src_bytes, ((u_char *)sf_buf_kva(zb->zb_pages[page])) +
                       poffset, count);
                   poffset += count;
                   if (poffset == PAGE_SIZE) {
                           poffset = 0;
                           page++;
                   }
                   KASSERT(poffset < PAGE_SIZE,
                       ("bpf_zerocopy_append_bytes: page offset overflow (%d)",
                       poffset));
                   len -= count;
                   src_bytes += count;
           }
   }
   
   /*
    * Copy bytes from an mbuf chain to the specified zbuf: copying will be
    * scatter-gather both from mbufs, which may be fragmented over memory, and
    * to pages, which may not be contiguously mapped in kernel address space.
    * As with bpf_zerocopy_append_bytes(), the caller is responsible for
    * checking that this will not exceed the buffer limit.
    */
   void
   bpf_zerocopy_append_mbuf(struct bpf_d *d, caddr_t buf, u_int offset,
       void *src, u_int len)
   {
           u_int count, moffset, page, poffset;
           const struct mbuf *m;
           struct zbuf *zb;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_append_mbuf not in zbuf mode"));
           KASSERT(buf != NULL, ("bpf_zerocopy_append_mbuf: NULL buf"));
   
           m = (struct mbuf *)src;
           zb = (struct zbuf *)buf;
   
           KASSERT((zb->zb_flags & ZBUF_FLAG_ASSIGNED) == 0,
               ("bpf_zerocopy_append_mbuf: ZBUF_FLAG_ASSIGNED"));
   
           /*
            * Scatter gather both from an mbuf chain and to a user page set
            * mapped into kernel address space using sf_bufs.  If we're lucky,
            * each mbuf requires one copy operation, but if page alignment and
            * mbuf alignment work out less well, we'll be doing two copies per
            * mbuf.
            */
           offset += sizeof(struct bpf_zbuf_header);
           page = offset / PAGE_SIZE;
           poffset = offset % PAGE_SIZE;
           moffset = 0;
           while (len > 0) {
                   KASSERT(page < zb->zb_numpages,
                       ("bpf_zerocopy_append_mbuf: page overflow (%d p %d "
                       "np)\n", page, zb->zb_numpages));
                   KASSERT(m != NULL,
                       ("bpf_zerocopy_append_mbuf: end of mbuf chain"));
   
                   count = min(m->m_len - moffset, len);
                   count = min(count, PAGE_SIZE - poffset);
                   bcopy(mtod(m, u_char *) + moffset,
                       ((u_char *)sf_buf_kva(zb->zb_pages[page])) + poffset,
                       count);
                   poffset += count;
                   if (poffset == PAGE_SIZE) {
                           poffset = 0;
                           page++;
                   }
                   KASSERT(poffset < PAGE_SIZE,
                       ("bpf_zerocopy_append_mbuf: page offset overflow (%d)",
                       poffset));
                   moffset += count;
                   if (moffset == m->m_len) {
                           m = m->m_next;
                           moffset = 0;
                   }
                   len -= count;
           }
   }
   
   /*
    * Notification from the BPF framework that a buffer in the store position is
    * rejecting packets and may be considered full.  We mark the buffer as
    * immutable and assign to userspace so that it is immediately available for
    * the user process to access.
    */
   void
   bpf_zerocopy_buffull(struct bpf_d *d)
   {
           struct zbuf *zb;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_buffull: not in zbuf mode"));
   
           zb = (struct zbuf *)d->bd_sbuf;
           KASSERT(zb != NULL, ("bpf_zerocopy_buffull: zb == NULL"));
   
           if ((zb->zb_flags & ZBUF_FLAG_ASSIGNED) == 0) {
                   zb->zb_flags |= ZBUF_FLAG_ASSIGNED;
                   zb->zb_header->bzh_kernel_len = d->bd_slen;
                   atomic_add_rel_int(&zb->zb_header->bzh_kernel_gen, 1);
           }
   }
   
   /*
    * Notification from the BPF framework that a buffer has moved into the held
    * slot on a descriptor.  Zero-copy BPF will update the shared page to let
    * the user process know and flag the buffer as assigned if it hasn't already
    * been marked assigned due to filling while it was in the store position.
    *
    * Note: identical logic as in bpf_zerocopy_buffull(), except that we operate
    * on bd_hbuf and bd_hlen.
    */
   void
   bpf_zerocopy_bufheld(struct bpf_d *d)
   {
           struct zbuf *zb;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_bufheld: not in zbuf mode"));
   
           zb = (struct zbuf *)d->bd_hbuf;
           KASSERT(zb != NULL, ("bpf_zerocopy_bufheld: zb == NULL"));
   
           if ((zb->zb_flags & ZBUF_FLAG_ASSIGNED) == 0) {
                   zb->zb_flags |= ZBUF_FLAG_ASSIGNED;
                   zb->zb_header->bzh_kernel_len = d->bd_hlen;
                   atomic_add_rel_int(&zb->zb_header->bzh_kernel_gen, 1);
           }
   }
   
   /*
    * Notification from the BPF framework that the free buffer has been been
    * rotated out of the held position to the free position.  This happens when
    * the user acknowledges the held buffer.
    */
   void
   bpf_zerocopy_buf_reclaimed(struct bpf_d *d)
   {
           struct zbuf *zb;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_reclaim_buf: not in zbuf mode"));
   
           KASSERT(d->bd_fbuf != NULL,
               ("bpf_zerocopy_buf_reclaimed: NULL free buf"));
           zb = (struct zbuf *)d->bd_fbuf;
           zb->zb_flags &= ~ZBUF_FLAG_ASSIGNED;
   }
   
   /*
    * Query from the BPF framework regarding whether the buffer currently in the
    * held position can be moved to the free position, which can be indicated by
    * the user process making their generation number equal to the kernel
    * generation number.
    */
   int
   bpf_zerocopy_canfreebuf(struct bpf_d *d)
   {
           struct zbuf *zb;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_canfreebuf: not in zbuf mode"));
   
           zb = (struct zbuf *)d->bd_hbuf;
           if (zb == NULL)
                   return (0);
           if (zb->zb_header->bzh_kernel_gen ==
               atomic_load_acq_int(&zb->zb_header->bzh_user_gen))
                   return (1);
           return (0);
   }
   
   /*
    * Query from the BPF framework as to whether or not the buffer current in
    * the store position can actually be written to.  This may return false if
    * the store buffer is assigned to userspace before the hold buffer is
    * acknowledged.
    */
   int
   bpf_zerocopy_canwritebuf(struct bpf_d *d)
   {
           struct zbuf *zb;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_canwritebuf: not in zbuf mode"));
   
           zb = (struct zbuf *)d->bd_sbuf;
           KASSERT(zb != NULL, ("bpf_zerocopy_canwritebuf: bd_sbuf NULL"));
   
           if (zb->zb_flags & ZBUF_FLAG_ASSIGNED)
                   return (0);
           return (1);
   }
   
   /*
    * Free zero copy buffers at request of descriptor.
    */
   void
   bpf_zerocopy_free(struct bpf_d *d)
   {
           struct zbuf *zb;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_free: not in zbuf mode"));
   
           zb = (struct zbuf *)d->bd_sbuf;
           if (zb != NULL)
                   zbuf_free(zb);
           zb = (struct zbuf *)d->bd_hbuf;
           if (zb != NULL)
                   zbuf_free(zb);
           zb = (struct zbuf *)d->bd_fbuf;
           if (zb != NULL)
                   zbuf_free(zb);
   }
   
   /*
    * Ioctl to return the maximum buffer size.
    */
   int
   bpf_zerocopy_ioctl_getzmax(struct thread *td, struct bpf_d *d, size_t *i)
   {
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_ioctl_getzmax: not in zbuf mode"));
   
           *i = BPF_MAX_PAGES * PAGE_SIZE;
           return (0);
   }
   
   /*
    * Ioctl to force rotation of the two buffers, if there's any data available.
    * This can be used by user space to implement timeouts when waiting for a
    * buffer to fill.
    */
   int
   bpf_zerocopy_ioctl_rotzbuf(struct thread *td, struct bpf_d *d,
       struct bpf_zbuf *bz)
   {
           struct zbuf *bzh;
   
           bzero(bz, sizeof(*bz));
           BPFD_LOCK(d);
           if (d->bd_hbuf == NULL && d->bd_slen != 0) {
                   ROTATE_BUFFERS(d);
                   bzh = (struct zbuf *)d->bd_hbuf;
                   bz->bz_bufa = (void *)bzh->zb_uaddr;
                   bz->bz_buflen = d->bd_hlen;
           }
           BPFD_UNLOCK(d);
           return (0);
   }
   
   /*
    * Ioctl to configure zero-copy buffers -- may be done only once.
    */
   int
   bpf_zerocopy_ioctl_setzbuf(struct thread *td, struct bpf_d *d,
       struct bpf_zbuf *bz)
   {
           struct zbuf *zba, *zbb;
           int error;
   
           KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
               ("bpf_zerocopy_ioctl_setzbuf: not in zbuf mode"));
   
           /*
            * Must set both buffers.  Cannot clear them.
            */
           if (bz->bz_bufa == NULL || bz->bz_bufb == NULL)
                   return (EINVAL);
   
           /*
            * Buffers must have a size greater than 0.  Alignment and other size
            * validity checking is done in zbuf_setup().
            */
           if (bz->bz_buflen == 0)
                   return (EINVAL);
   
           /*
            * Allocate new buffers.
            */
           error = zbuf_setup(td, (vm_offset_t)bz->bz_bufa, bz->bz_buflen,
               &zba);
           if (error)
                   return (error);
           error = zbuf_setup(td, (vm_offset_t)bz->bz_bufb, bz->bz_buflen,
               &zbb);
           if (error) {
                   zbuf_free(zba);
                   return (error);
           }
   
           /*
            * We only allow buffers to be installed once, so atomically check
            * that no buffers are currently installed and install new buffers.
            */
           BPFD_LOCK(d);
           if (d->bd_hbuf != NULL || d->bd_sbuf != NULL || d->bd_fbuf != NULL ||
               d->bd_bif != NULL) {
                   BPFD_UNLOCK(d);
                   zbuf_free(zba);
                   zbuf_free(zbb);
                   return (EINVAL);
           }
   
           /*
            * Point BPF descriptor at buffers; initialize sbuf as zba so that
            * it is always filled first in the sequence, per bpf(4).
            */
           d->bd_fbuf = (caddr_t)zbb;
           d->bd_sbuf = (caddr_t)zba;
           d->bd_slen = 0;
           d->bd_hlen = 0;
   
           /*
            * We expose only the space left in the buffer after the size of the
            * shared management region.
            */
           d->bd_bufsize = bz->bz_buflen - sizeof(struct bpf_zbuf_header);
           BPFD_UNLOCK(d);
           return (0);
   }

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