Commit 0185cfb3 authored by Dr. David Alan Gilbert's avatar Dr. David Alan Gilbert Committed by Michael S. Tsirkin
Browse files

libvhost-user: mprotect & madvises for postcopy 



Clear the area and turn off THP.
PROT_NONE the area until after we've userfault advised it
to catch any unexpected changes.

Signed-off-by: default avatarDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: default avatarMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent dedfb4b2

contrib/libvhost-user/libvhost-user.c

+42 −5
Original line number Diff line number Diff line
@@ -454,7 +454,7 @@ vu_set_mem_table_exec_postcopy(VuDev *dev, VhostUserMsg *vmsg) 
    int i;

    VhostUserMemory *memory = &vmsg->payload.memory;

    dev->nregions = memory->nregions;

    /* TODO: Postcopy specific code */



    DPRINT("Nregions: %d\n", memory->nregions);

    for (i = 0; i < dev->nregions; i++) {

        void *mmap_addr;
@@ -478,9 +478,12 @@ vu_set_mem_table_exec_postcopy(VuDev *dev, VhostUserMsg *vmsg) 


        /* We don't use offset argument of mmap() since the

         * mapped address has to be page aligned, and we use huge

         * pages.  */

         * pages.

         * In postcopy we're using PROT_NONE here to catch anyone

         * accessing it before we userfault

         */

        mmap_addr = mmap(0, dev_region->size + dev_region->mmap_offset,

                         PROT_READ | PROT_WRITE, MAP_SHARED,

                         PROT_NONE, MAP_SHARED,

                         vmsg->fds[i], 0);



        if (mmap_addr == MAP_FAILED) {
@@ -519,12 +522,38 @@ vu_set_mem_table_exec_postcopy(VuDev *dev, VhostUserMsg *vmsg) 
    /* OK, now we can go and register the memory and generate faults */

    for (i = 0; i < dev->nregions; i++) {

        VuDevRegion *dev_region = &dev->regions[i];

        int ret;

#ifdef UFFDIO_REGISTER

        /* We should already have an open ufd. Mark each memory

         * range as ufd.

         * Note: Do we need any madvises? Well it's not been accessed

         * yet, still probably need no THP to be safe, discard to be safe?

         * Discard any mapping we have here; note I can't use MADV_REMOVE

         * or fallocate to make the hole since I don't want to lose

         * data that's already arrived in the shared process.

         * TODO: How to do hugepage

         */

        ret = madvise((void *)dev_region->mmap_addr,

                      dev_region->size + dev_region->mmap_offset,

                      MADV_DONTNEED);

        if (ret) {

            fprintf(stderr,

                    "%s: Failed to madvise(DONTNEED) region %d: %s\n",

                    __func__, i, strerror(errno));

        }

        /* Turn off transparent hugepages so we dont get lose wakeups

         * in neighbouring pages.

         * TODO: Turn this backon later.

         */

        ret = madvise((void *)dev_region->mmap_addr,

                      dev_region->size + dev_region->mmap_offset,

                      MADV_NOHUGEPAGE);

        if (ret) {

            /* Note: This can happen legally on kernels that are configured

             * without madvise'able hugepages

             */

            fprintf(stderr,

                    "%s: Failed to madvise(NOHUGEPAGE) region %d: %s\n",

                    __func__, i, strerror(errno));

        }

        struct uffdio_register reg_struct;

        reg_struct.range.start = (uintptr_t)dev_region->mmap_addr;

        reg_struct.range.len = dev_region->size + dev_region->mmap_offset;
@@ -546,6 +575,14 @@ vu_set_mem_table_exec_postcopy(VuDev *dev, VhostUserMsg *vmsg) 
        }

        DPRINT("%s: region %d: Registered userfault for %llx + %llx\n",

                __func__, i, reg_struct.range.start, reg_struct.range.len);

        /* Now it's registered we can let the client at it */

        if (mprotect((void *)dev_region->mmap_addr,

                     dev_region->size + dev_region->mmap_offset,

                     PROT_READ | PROT_WRITE)) {

            vu_panic(dev, "failed to mprotect region %d for postcopy (%s)",

                     i, strerror(errno));

            return false;

        }

        /* TODO: Stash 'zero' support flags somewhere */

#endif

    }