Message ID | 20200226155304.60219-11-david@redhat.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | migrate/ram: Fix resizing RAM blocks while migrating | expand |
* David Hildenbrand (david@redhat.com) wrote: > Resizing while migrating is dangerous and does not work as expected. > The whole migration code works on the usable_length of ram blocks and does > not expect this to change at random points in time. > > In the case of postcopy, relying on used_length is racy as soon as the > guest is running. Also, when used_length changes we might leave the > uffd handler registered for some memory regions, reject valid pages > when migrating and fail when sending the recv bitmap to the source. > > Resizing can be trigger *after* (but not during) a reset in > ACPI code by the guest > - hw/arm/virt-acpi-build.c:acpi_ram_update() > - hw/i386/acpi-build.c:acpi_ram_update() > > Let's remember the original used_length in a separate variable and > use it in relevant postcopy code. Make sure to update it when we resize > during precopy, when synchronizing the RAM block sizes with the source. > > Reviewed-by: Peter Xu <peterx@redhat.com> > Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com> > Cc: Juan Quintela <quintela@redhat.com> > Cc: Eduardo Habkost <ehabkost@redhat.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Igor Mammedov <imammedo@redhat.com> > Cc: "Michael S. Tsirkin" <mst@redhat.com> > Cc: Richard Henderson <richard.henderson@linaro.org> > Cc: Shannon Zhao <shannon.zhao@linaro.org> > Cc: Alex Bennée <alex.bennee@linaro.org> > Cc: Peter Xu <peterx@redhat.com> > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > include/exec/ramblock.h | 10 ++++++++++ > migration/postcopy-ram.c | 15 ++++++++++++--- > migration/ram.c | 11 +++++++++-- > 3 files changed, 31 insertions(+), 5 deletions(-) > > diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h > index 07d50864d8..664701b759 100644 > --- a/include/exec/ramblock.h > +++ b/include/exec/ramblock.h > @@ -59,6 +59,16 @@ struct RAMBlock { > */ > unsigned long *clear_bmap; > uint8_t clear_bmap_shift; > + > + /* > + * RAM block length that corresponds to the used_length on the migration > + * source (after RAM block sizes were synchronized). Especially, after > + * starting to run the guest, used_length and postcopy_length can differ. > + * Used to register/unregister uffd handlers and as the size of the received > + * bitmap. Receiving any page beyond this length will bail out, as it > + * could not have been valid on the source. > + */ > + ram_addr_t postcopy_length; > }; > #endif > #endif > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index a36402722b..c68caf4e42 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -17,6 +17,7 @@ > */ > > #include "qemu/osdep.h" > +#include "qemu/rcu.h" > #include "exec/target_page.h" > #include "migration.h" > #include "qemu-file.h" > @@ -31,6 +32,7 @@ > #include "qemu/error-report.h" > #include "trace.h" > #include "hw/boards.h" > +#include "exec/ramblock.h" > > /* Arbitrary limit on size of each discard command, > * keeps them around ~200 bytes > @@ -456,6 +458,13 @@ static int init_range(RAMBlock *rb, void *opaque) > ram_addr_t length = qemu_ram_get_used_length(rb); > trace_postcopy_init_range(block_name, host_addr, offset, length); > > + /* > + * Save the used_length before running the guest. In case we have to > + * resize RAM blocks when syncing RAM block sizes from the source during > + * precopy, we'll update it manually via the ram block notifier. > + */ > + rb->postcopy_length = length; > + > /* > * We need the whole of RAM to be truly empty for postcopy, so things > * like ROMs and any data tables built during init must be zero'd > @@ -478,7 +487,7 @@ static int cleanup_range(RAMBlock *rb, void *opaque) > const char *block_name = qemu_ram_get_idstr(rb); > void *host_addr = qemu_ram_get_host_addr(rb); > ram_addr_t offset = qemu_ram_get_offset(rb); > - ram_addr_t length = qemu_ram_get_used_length(rb); > + ram_addr_t length = rb->postcopy_length; > MigrationIncomingState *mis = opaque; > struct uffdio_range range_struct; > trace_postcopy_cleanup_range(block_name, host_addr, offset, length); > @@ -600,7 +609,7 @@ static int nhp_range(RAMBlock *rb, void *opaque) > const char *block_name = qemu_ram_get_idstr(rb); > void *host_addr = qemu_ram_get_host_addr(rb); > ram_addr_t offset = qemu_ram_get_offset(rb); > - ram_addr_t length = qemu_ram_get_used_length(rb); > + ram_addr_t length = rb->postcopy_length; > trace_postcopy_nhp_range(block_name, host_addr, offset, length); > > /* > @@ -644,7 +653,7 @@ static int ram_block_enable_notify(RAMBlock *rb, void *opaque) > struct uffdio_register reg_struct; > > reg_struct.range.start = (uintptr_t)qemu_ram_get_host_addr(rb); > - reg_struct.range.len = qemu_ram_get_used_length(rb); > + reg_struct.range.len = rb->postcopy_length; > reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING; > > /* Now tell our userfault_fd that it's responsible for this area */ > diff --git a/migration/ram.c b/migration/ram.c > index 1a5ff07997..ee5c3d5784 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -244,7 +244,7 @@ int64_t ramblock_recv_bitmap_send(QEMUFile *file, > return -1; > } > > - nbits = block->used_length >> TARGET_PAGE_BITS; > + nbits = block->postcopy_length >> TARGET_PAGE_BITS; > > /* > * Make sure the tmp bitmap buffer is big enough, e.g., on 32bit > @@ -3160,7 +3160,13 @@ static int ram_load_postcopy(QEMUFile *f) > break; > } > > - if (!offset_in_ramblock(block, addr)) { > + /* > + * Relying on used_length is racy and can result in false positives. > + * We might place pages beyond used_length in case RAM was shrunk > + * while in postcopy, which is fine - trying to place via > + * UFFDIO_COPY/UFFDIO_ZEROPAGE will never segfault. > + */ Is this actually safe? Imagine that the region had got shrunk, would it still be mmap'd in there - or could there now be a space where something else might have landed in? > + if (!block->host || addr >= block->postcopy_length) { > error_report("Illegal RAM offset " RAM_ADDR_FMT, addr); > ret = -EINVAL; > break; > @@ -3757,6 +3763,7 @@ static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host, > rb->idstr); > } > } > + rb->postcopy_length = new_size; > break; > case POSTCOPY_INCOMING_NONE: > case POSTCOPY_INCOMING_RUNNING: > -- > 2.24.1 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
On 06.03.20 17:56, Dr. David Alan Gilbert wrote: > * David Hildenbrand (david@redhat.com) wrote: >> Resizing while migrating is dangerous and does not work as expected. >> The whole migration code works on the usable_length of ram blocks and does >> not expect this to change at random points in time. >> >> In the case of postcopy, relying on used_length is racy as soon as the >> guest is running. Also, when used_length changes we might leave the >> uffd handler registered for some memory regions, reject valid pages >> when migrating and fail when sending the recv bitmap to the source. >> >> Resizing can be trigger *after* (but not during) a reset in >> ACPI code by the guest >> - hw/arm/virt-acpi-build.c:acpi_ram_update() >> - hw/i386/acpi-build.c:acpi_ram_update() >> >> Let's remember the original used_length in a separate variable and >> use it in relevant postcopy code. Make sure to update it when we resize >> during precopy, when synchronizing the RAM block sizes with the source. >> >> Reviewed-by: Peter Xu <peterx@redhat.com> >> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com> >> Cc: Juan Quintela <quintela@redhat.com> >> Cc: Eduardo Habkost <ehabkost@redhat.com> >> Cc: Paolo Bonzini <pbonzini@redhat.com> >> Cc: Igor Mammedov <imammedo@redhat.com> >> Cc: "Michael S. Tsirkin" <mst@redhat.com> >> Cc: Richard Henderson <richard.henderson@linaro.org> >> Cc: Shannon Zhao <shannon.zhao@linaro.org> >> Cc: Alex Bennée <alex.bennee@linaro.org> >> Cc: Peter Xu <peterx@redhat.com> >> Signed-off-by: David Hildenbrand <david@redhat.com> >> --- >> include/exec/ramblock.h | 10 ++++++++++ >> migration/postcopy-ram.c | 15 ++++++++++++--- >> migration/ram.c | 11 +++++++++-- >> 3 files changed, 31 insertions(+), 5 deletions(-) >> >> diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h >> index 07d50864d8..664701b759 100644 >> --- a/include/exec/ramblock.h >> +++ b/include/exec/ramblock.h >> @@ -59,6 +59,16 @@ struct RAMBlock { >> */ >> unsigned long *clear_bmap; >> uint8_t clear_bmap_shift; >> + >> + /* >> + * RAM block length that corresponds to the used_length on the migration >> + * source (after RAM block sizes were synchronized). Especially, after >> + * starting to run the guest, used_length and postcopy_length can differ. >> + * Used to register/unregister uffd handlers and as the size of the received >> + * bitmap. Receiving any page beyond this length will bail out, as it >> + * could not have been valid on the source. >> + */ >> + ram_addr_t postcopy_length; >> }; >> #endif >> #endif >> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c >> index a36402722b..c68caf4e42 100644 >> --- a/migration/postcopy-ram.c >> +++ b/migration/postcopy-ram.c >> @@ -17,6 +17,7 @@ >> */ >> >> #include "qemu/osdep.h" >> +#include "qemu/rcu.h" >> #include "exec/target_page.h" >> #include "migration.h" >> #include "qemu-file.h" >> @@ -31,6 +32,7 @@ >> #include "qemu/error-report.h" >> #include "trace.h" >> #include "hw/boards.h" >> +#include "exec/ramblock.h" >> >> /* Arbitrary limit on size of each discard command, >> * keeps them around ~200 bytes >> @@ -456,6 +458,13 @@ static int init_range(RAMBlock *rb, void *opaque) >> ram_addr_t length = qemu_ram_get_used_length(rb); >> trace_postcopy_init_range(block_name, host_addr, offset, length); >> >> + /* >> + * Save the used_length before running the guest. In case we have to >> + * resize RAM blocks when syncing RAM block sizes from the source during >> + * precopy, we'll update it manually via the ram block notifier. >> + */ >> + rb->postcopy_length = length; >> + >> /* >> * We need the whole of RAM to be truly empty for postcopy, so things >> * like ROMs and any data tables built during init must be zero'd >> @@ -478,7 +487,7 @@ static int cleanup_range(RAMBlock *rb, void *opaque) >> const char *block_name = qemu_ram_get_idstr(rb); >> void *host_addr = qemu_ram_get_host_addr(rb); >> ram_addr_t offset = qemu_ram_get_offset(rb); >> - ram_addr_t length = qemu_ram_get_used_length(rb); >> + ram_addr_t length = rb->postcopy_length; >> MigrationIncomingState *mis = opaque; >> struct uffdio_range range_struct; >> trace_postcopy_cleanup_range(block_name, host_addr, offset, length); >> @@ -600,7 +609,7 @@ static int nhp_range(RAMBlock *rb, void *opaque) >> const char *block_name = qemu_ram_get_idstr(rb); >> void *host_addr = qemu_ram_get_host_addr(rb); >> ram_addr_t offset = qemu_ram_get_offset(rb); >> - ram_addr_t length = qemu_ram_get_used_length(rb); >> + ram_addr_t length = rb->postcopy_length; >> trace_postcopy_nhp_range(block_name, host_addr, offset, length); >> >> /* >> @@ -644,7 +653,7 @@ static int ram_block_enable_notify(RAMBlock *rb, void *opaque) >> struct uffdio_register reg_struct; >> >> reg_struct.range.start = (uintptr_t)qemu_ram_get_host_addr(rb); >> - reg_struct.range.len = qemu_ram_get_used_length(rb); >> + reg_struct.range.len = rb->postcopy_length; >> reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING; >> >> /* Now tell our userfault_fd that it's responsible for this area */ >> diff --git a/migration/ram.c b/migration/ram.c >> index 1a5ff07997..ee5c3d5784 100644 >> --- a/migration/ram.c >> +++ b/migration/ram.c >> @@ -244,7 +244,7 @@ int64_t ramblock_recv_bitmap_send(QEMUFile *file, >> return -1; >> } >> >> - nbits = block->used_length >> TARGET_PAGE_BITS; >> + nbits = block->postcopy_length >> TARGET_PAGE_BITS; >> >> /* >> * Make sure the tmp bitmap buffer is big enough, e.g., on 32bit >> @@ -3160,7 +3160,13 @@ static int ram_load_postcopy(QEMUFile *f) >> break; >> } >> >> - if (!offset_in_ramblock(block, addr)) { >> + /* >> + * Relying on used_length is racy and can result in false positives. >> + * We might place pages beyond used_length in case RAM was shrunk >> + * while in postcopy, which is fine - trying to place via >> + * UFFDIO_COPY/UFFDIO_ZEROPAGE will never segfault. >> + */ > > Is this actually safe? Imagine that the region had got shrunk, would it > still be mmap'd in there - or could there now be a space where something > else might have landed in? Yes, it's safe. The mapping of resizeable RAM blocks will currently not change when resized. See patch #13 on how this is handled when the mapping actually change (preparation for resizeable allocations [1]). [1] https://lore.kernel.org/qemu-devel/20200305142945.216465-1-david@redhat.com/
* David Hildenbrand (david@redhat.com) wrote: > On 06.03.20 17:56, Dr. David Alan Gilbert wrote: > > * David Hildenbrand (david@redhat.com) wrote: > >> Resizing while migrating is dangerous and does not work as expected. > >> The whole migration code works on the usable_length of ram blocks and does > >> not expect this to change at random points in time. > >> > >> In the case of postcopy, relying on used_length is racy as soon as the > >> guest is running. Also, when used_length changes we might leave the > >> uffd handler registered for some memory regions, reject valid pages > >> when migrating and fail when sending the recv bitmap to the source. > >> > >> Resizing can be trigger *after* (but not during) a reset in > >> ACPI code by the guest > >> - hw/arm/virt-acpi-build.c:acpi_ram_update() > >> - hw/i386/acpi-build.c:acpi_ram_update() > >> > >> Let's remember the original used_length in a separate variable and > >> use it in relevant postcopy code. Make sure to update it when we resize > >> during precopy, when synchronizing the RAM block sizes with the source. > >> > >> Reviewed-by: Peter Xu <peterx@redhat.com> > >> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com> > >> Cc: Juan Quintela <quintela@redhat.com> > >> Cc: Eduardo Habkost <ehabkost@redhat.com> > >> Cc: Paolo Bonzini <pbonzini@redhat.com> > >> Cc: Igor Mammedov <imammedo@redhat.com> > >> Cc: "Michael S. Tsirkin" <mst@redhat.com> > >> Cc: Richard Henderson <richard.henderson@linaro.org> > >> Cc: Shannon Zhao <shannon.zhao@linaro.org> > >> Cc: Alex Bennée <alex.bennee@linaro.org> > >> Cc: Peter Xu <peterx@redhat.com> > >> Signed-off-by: David Hildenbrand <david@redhat.com> > >> --- > >> include/exec/ramblock.h | 10 ++++++++++ > >> migration/postcopy-ram.c | 15 ++++++++++++--- > >> migration/ram.c | 11 +++++++++-- > >> 3 files changed, 31 insertions(+), 5 deletions(-) > >> > >> diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h > >> index 07d50864d8..664701b759 100644 > >> --- a/include/exec/ramblock.h > >> +++ b/include/exec/ramblock.h > >> @@ -59,6 +59,16 @@ struct RAMBlock { > >> */ > >> unsigned long *clear_bmap; > >> uint8_t clear_bmap_shift; > >> + > >> + /* > >> + * RAM block length that corresponds to the used_length on the migration > >> + * source (after RAM block sizes were synchronized). Especially, after > >> + * starting to run the guest, used_length and postcopy_length can differ. > >> + * Used to register/unregister uffd handlers and as the size of the received > >> + * bitmap. Receiving any page beyond this length will bail out, as it > >> + * could not have been valid on the source. > >> + */ > >> + ram_addr_t postcopy_length; > >> }; > >> #endif > >> #endif > >> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > >> index a36402722b..c68caf4e42 100644 > >> --- a/migration/postcopy-ram.c > >> +++ b/migration/postcopy-ram.c > >> @@ -17,6 +17,7 @@ > >> */ > >> > >> #include "qemu/osdep.h" > >> +#include "qemu/rcu.h" > >> #include "exec/target_page.h" > >> #include "migration.h" > >> #include "qemu-file.h" > >> @@ -31,6 +32,7 @@ > >> #include "qemu/error-report.h" > >> #include "trace.h" > >> #include "hw/boards.h" > >> +#include "exec/ramblock.h" > >> > >> /* Arbitrary limit on size of each discard command, > >> * keeps them around ~200 bytes > >> @@ -456,6 +458,13 @@ static int init_range(RAMBlock *rb, void *opaque) > >> ram_addr_t length = qemu_ram_get_used_length(rb); > >> trace_postcopy_init_range(block_name, host_addr, offset, length); > >> > >> + /* > >> + * Save the used_length before running the guest. In case we have to > >> + * resize RAM blocks when syncing RAM block sizes from the source during > >> + * precopy, we'll update it manually via the ram block notifier. > >> + */ > >> + rb->postcopy_length = length; > >> + > >> /* > >> * We need the whole of RAM to be truly empty for postcopy, so things > >> * like ROMs and any data tables built during init must be zero'd > >> @@ -478,7 +487,7 @@ static int cleanup_range(RAMBlock *rb, void *opaque) > >> const char *block_name = qemu_ram_get_idstr(rb); > >> void *host_addr = qemu_ram_get_host_addr(rb); > >> ram_addr_t offset = qemu_ram_get_offset(rb); > >> - ram_addr_t length = qemu_ram_get_used_length(rb); > >> + ram_addr_t length = rb->postcopy_length; > >> MigrationIncomingState *mis = opaque; > >> struct uffdio_range range_struct; > >> trace_postcopy_cleanup_range(block_name, host_addr, offset, length); > >> @@ -600,7 +609,7 @@ static int nhp_range(RAMBlock *rb, void *opaque) > >> const char *block_name = qemu_ram_get_idstr(rb); > >> void *host_addr = qemu_ram_get_host_addr(rb); > >> ram_addr_t offset = qemu_ram_get_offset(rb); > >> - ram_addr_t length = qemu_ram_get_used_length(rb); > >> + ram_addr_t length = rb->postcopy_length; > >> trace_postcopy_nhp_range(block_name, host_addr, offset, length); > >> > >> /* > >> @@ -644,7 +653,7 @@ static int ram_block_enable_notify(RAMBlock *rb, void *opaque) > >> struct uffdio_register reg_struct; > >> > >> reg_struct.range.start = (uintptr_t)qemu_ram_get_host_addr(rb); > >> - reg_struct.range.len = qemu_ram_get_used_length(rb); > >> + reg_struct.range.len = rb->postcopy_length; > >> reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING; > >> > >> /* Now tell our userfault_fd that it's responsible for this area */ > >> diff --git a/migration/ram.c b/migration/ram.c > >> index 1a5ff07997..ee5c3d5784 100644 > >> --- a/migration/ram.c > >> +++ b/migration/ram.c > >> @@ -244,7 +244,7 @@ int64_t ramblock_recv_bitmap_send(QEMUFile *file, > >> return -1; > >> } > >> > >> - nbits = block->used_length >> TARGET_PAGE_BITS; > >> + nbits = block->postcopy_length >> TARGET_PAGE_BITS; > >> > >> /* > >> * Make sure the tmp bitmap buffer is big enough, e.g., on 32bit > >> @@ -3160,7 +3160,13 @@ static int ram_load_postcopy(QEMUFile *f) > >> break; > >> } > >> > >> - if (!offset_in_ramblock(block, addr)) { > >> + /* > >> + * Relying on used_length is racy and can result in false positives. > >> + * We might place pages beyond used_length in case RAM was shrunk > >> + * while in postcopy, which is fine - trying to place via > >> + * UFFDIO_COPY/UFFDIO_ZEROPAGE will never segfault. > >> + */ > > > > Is this actually safe? Imagine that the region had got shrunk, would it > > still be mmap'd in there - or could there now be a space where something > > else might have landed in? > > Yes, it's safe. The mapping of resizeable RAM blocks will currently not > change when resized. See patch #13 on how this is handled when the > mapping actually change (preparation for resizeable allocations [1]). OK, in that case, Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > [1] > https://lore.kernel.org/qemu-devel/20200305142945.216465-1-david@redhat.com/ > > -- > Thanks, > > David / dhildenb -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h index 07d50864d8..664701b759 100644 --- a/include/exec/ramblock.h +++ b/include/exec/ramblock.h @@ -59,6 +59,16 @@ struct RAMBlock { */ unsigned long *clear_bmap; uint8_t clear_bmap_shift; + + /* + * RAM block length that corresponds to the used_length on the migration + * source (after RAM block sizes were synchronized). Especially, after + * starting to run the guest, used_length and postcopy_length can differ. + * Used to register/unregister uffd handlers and as the size of the received + * bitmap. Receiving any page beyond this length will bail out, as it + * could not have been valid on the source. + */ + ram_addr_t postcopy_length; }; #endif #endif diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c index a36402722b..c68caf4e42 100644 --- a/migration/postcopy-ram.c +++ b/migration/postcopy-ram.c @@ -17,6 +17,7 @@ */ #include "qemu/osdep.h" +#include "qemu/rcu.h" #include "exec/target_page.h" #include "migration.h" #include "qemu-file.h" @@ -31,6 +32,7 @@ #include "qemu/error-report.h" #include "trace.h" #include "hw/boards.h" +#include "exec/ramblock.h" /* Arbitrary limit on size of each discard command, * keeps them around ~200 bytes @@ -456,6 +458,13 @@ static int init_range(RAMBlock *rb, void *opaque) ram_addr_t length = qemu_ram_get_used_length(rb); trace_postcopy_init_range(block_name, host_addr, offset, length); + /* + * Save the used_length before running the guest. In case we have to + * resize RAM blocks when syncing RAM block sizes from the source during + * precopy, we'll update it manually via the ram block notifier. + */ + rb->postcopy_length = length; + /* * We need the whole of RAM to be truly empty for postcopy, so things * like ROMs and any data tables built during init must be zero'd @@ -478,7 +487,7 @@ static int cleanup_range(RAMBlock *rb, void *opaque) const char *block_name = qemu_ram_get_idstr(rb); void *host_addr = qemu_ram_get_host_addr(rb); ram_addr_t offset = qemu_ram_get_offset(rb); - ram_addr_t length = qemu_ram_get_used_length(rb); + ram_addr_t length = rb->postcopy_length; MigrationIncomingState *mis = opaque; struct uffdio_range range_struct; trace_postcopy_cleanup_range(block_name, host_addr, offset, length); @@ -600,7 +609,7 @@ static int nhp_range(RAMBlock *rb, void *opaque) const char *block_name = qemu_ram_get_idstr(rb); void *host_addr = qemu_ram_get_host_addr(rb); ram_addr_t offset = qemu_ram_get_offset(rb); - ram_addr_t length = qemu_ram_get_used_length(rb); + ram_addr_t length = rb->postcopy_length; trace_postcopy_nhp_range(block_name, host_addr, offset, length); /* @@ -644,7 +653,7 @@ static int ram_block_enable_notify(RAMBlock *rb, void *opaque) struct uffdio_register reg_struct; reg_struct.range.start = (uintptr_t)qemu_ram_get_host_addr(rb); - reg_struct.range.len = qemu_ram_get_used_length(rb); + reg_struct.range.len = rb->postcopy_length; reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING; /* Now tell our userfault_fd that it's responsible for this area */ diff --git a/migration/ram.c b/migration/ram.c index 1a5ff07997..ee5c3d5784 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -244,7 +244,7 @@ int64_t ramblock_recv_bitmap_send(QEMUFile *file, return -1; } - nbits = block->used_length >> TARGET_PAGE_BITS; + nbits = block->postcopy_length >> TARGET_PAGE_BITS; /* * Make sure the tmp bitmap buffer is big enough, e.g., on 32bit @@ -3160,7 +3160,13 @@ static int ram_load_postcopy(QEMUFile *f) break; } - if (!offset_in_ramblock(block, addr)) { + /* + * Relying on used_length is racy and can result in false positives. + * We might place pages beyond used_length in case RAM was shrunk + * while in postcopy, which is fine - trying to place via + * UFFDIO_COPY/UFFDIO_ZEROPAGE will never segfault. + */ + if (!block->host || addr >= block->postcopy_length) { error_report("Illegal RAM offset " RAM_ADDR_FMT, addr); ret = -EINVAL; break; @@ -3757,6 +3763,7 @@ static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host, rb->idstr); } } + rb->postcopy_length = new_size; break; case POSTCOPY_INCOMING_NONE: case POSTCOPY_INCOMING_RUNNING: