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postcopy_ram.c: place_page and helpers
postcopy_place_page (etc) provide a way for postcopy to place a page into guests memory atomically (using the copy ioctl on the ufd). Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Reviewed-by: Amit Shah <amit.shah@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> Signed-off-by: Juan Quintela <quintela@redhat.com>
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@ -96,6 +96,7 @@ struct MigrationIncomingState {
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int userfault_fd;
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QEMUFile *to_src_file;
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QemuMutex rp_mutex; /* We send replies from multiple threads */
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void *postcopy_tmp_page;
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/* See savevm.c */
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LoadStateEntry_Head loadvm_handlers;
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@ -69,4 +69,25 @@ void postcopy_discard_send_range(MigrationState *ms, PostcopyDiscardState *pds,
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void postcopy_discard_send_finish(MigrationState *ms,
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PostcopyDiscardState *pds);
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/*
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* Place a page (from) at (host) efficiently
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* There are restrictions on how 'from' must be mapped, in general best
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* to use other postcopy_ routines to allocate.
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* returns 0 on success
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*/
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int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from);
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/*
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* Place a zero page at (host) atomically
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* returns 0 on success
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*/
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int postcopy_place_page_zero(MigrationIncomingState *mis, void *host);
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/*
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* Allocate a page of memory that can be mapped at a later point in time
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* using postcopy_place_page
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* Returns: Pointer to allocated page
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*/
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void *postcopy_get_tmp_page(MigrationIncomingState *mis);
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#endif
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@ -272,6 +272,10 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
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return -1;
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}
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if (mis->postcopy_tmp_page) {
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munmap(mis->postcopy_tmp_page, getpagesize());
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mis->postcopy_tmp_page = NULL;
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}
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return 0;
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}
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@ -338,6 +342,83 @@ int postcopy_ram_enable_notify(MigrationIncomingState *mis)
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return 0;
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}
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/*
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* Place a host page (from) at (host) atomically
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* returns 0 on success
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*/
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int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from)
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{
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struct uffdio_copy copy_struct;
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copy_struct.dst = (uint64_t)(uintptr_t)host;
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copy_struct.src = (uint64_t)(uintptr_t)from;
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copy_struct.len = getpagesize();
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copy_struct.mode = 0;
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/* copy also acks to the kernel waking the stalled thread up
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* TODO: We can inhibit that ack and only do it if it was requested
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* which would be slightly cheaper, but we'd have to be careful
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* of the order of updating our page state.
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*/
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if (ioctl(mis->userfault_fd, UFFDIO_COPY, ©_struct)) {
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int e = errno;
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error_report("%s: %s copy host: %p from: %p",
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__func__, strerror(e), host, from);
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return -e;
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}
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trace_postcopy_place_page(host);
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return 0;
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}
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/*
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* Place a zero page at (host) atomically
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* returns 0 on success
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*/
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int postcopy_place_page_zero(MigrationIncomingState *mis, void *host)
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{
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struct uffdio_zeropage zero_struct;
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zero_struct.range.start = (uint64_t)(uintptr_t)host;
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zero_struct.range.len = getpagesize();
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zero_struct.mode = 0;
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if (ioctl(mis->userfault_fd, UFFDIO_ZEROPAGE, &zero_struct)) {
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int e = errno;
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error_report("%s: %s zero host: %p",
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__func__, strerror(e), host);
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return -e;
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}
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trace_postcopy_place_page_zero(host);
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return 0;
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}
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/*
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* Returns a target page of memory that can be mapped at a later point in time
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* using postcopy_place_page
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* The same address is used repeatedly, postcopy_place_page just takes the
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* backing page away.
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* Returns: Pointer to allocated page
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*
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*/
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void *postcopy_get_tmp_page(MigrationIncomingState *mis)
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{
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if (!mis->postcopy_tmp_page) {
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mis->postcopy_tmp_page = mmap(NULL, getpagesize(),
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PROT_READ | PROT_WRITE, MAP_PRIVATE |
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MAP_ANONYMOUS, -1, 0);
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if (!mis->postcopy_tmp_page) {
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error_report("%s: %s", __func__, strerror(errno));
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return NULL;
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}
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}
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return mis->postcopy_tmp_page;
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}
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#else
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/* No target OS support, stubs just fail */
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bool postcopy_ram_supported_by_host(void)
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@ -370,6 +451,25 @@ int postcopy_ram_enable_notify(MigrationIncomingState *mis)
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assert(0);
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return -1;
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}
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int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from)
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{
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assert(0);
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return -1;
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}
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int postcopy_place_page_zero(MigrationIncomingState *mis, void *host)
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{
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assert(0);
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return -1;
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}
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void *postcopy_get_tmp_page(MigrationIncomingState *mis)
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{
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assert(0);
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return NULL;
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}
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#endif
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/* ------------------------------------------------------------------------- */
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@ -1551,6 +1551,8 @@ postcopy_discard_send_range(const char *ramblock, unsigned long start, unsigned
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postcopy_ram_discard_range(void *start, size_t length) "%p,+%zx"
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postcopy_cleanup_range(const char *ramblock, void *host_addr, size_t offset, size_t length) "%s: %p offset=%zx length=%zx"
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postcopy_init_range(const char *ramblock, void *host_addr, size_t offset, size_t length) "%s: %p offset=%zx length=%zx"
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postcopy_place_page(void *host_addr) "host=%p"
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postcopy_place_page_zero(void *host_addr) "host=%p"
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# kvm-all.c
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kvm_ioctl(int type, void *arg) "type 0x%x, arg %p"
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