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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: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Dr. David Alan Gilbert 2018-03-12 17:21:18 +00:00 committed by Michael S. Tsirkin
parent dedfb4b21a
commit 0185cfb30b
1 changed files with 42 additions and 5 deletions
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47
contrib/libvhost-user/libvhost-user.c
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@ -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
}