When option -mem-prealloc is used with one or more memory-backend
objects, created backends may not obey configured bind policy or
creation may fail after kernel attempts to move pages according
to bind policy.
Reason is in file_ram_alloc(), which will pre-allocate
any descriptor based RAM if global mem_prealloc != 0 and that
happens way before bind policy is applied to memory range.
One way to fix it would be to extend memory_region_foo() API
and add more invariants that could broken later due implicit
dependencies that's hard to track.
Another approach is to drop adhoc main RAM allocation and
consolidate it around memory-backend. That allows to have
single place that allocates guest RAM (main and memdev)
in the same way and then global mem_prealloc could be
replaced by backend's property[s] that will affect created
memory-backend objects but only in correct order this time.
With main RAM now converted to hostmem backends, there is no
point in keeping global mem_prealloc around, so alias
-mem-prealloc to "memory-backend.prealloc=on"
machine compat[*] property and make mem_prealloc a local
variable to only stir registration of compat property.
*) currently user accessible -global works only with DEVICE
based objects and extra work is needed to make it work
with hostmem backends. But that is convenience option
and out of scope of this already huge refactoring.
Hence machine compat properties were used.
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20200219160953.13771-78-imammedo@redhat.com>
If seals are not supported, memfd_create() will fail.
Furthermore, there is no way to disable it in this case because
'.seal' property is not registered.
This issue leads to vhost-user-test failures on RHEL 7.2:
qemu-system-x86_64: -object memory-backend-memfd,id=mem,size=2M,: \
failed to create memfd: Invalid argument
and actually breaks the feature on such systems.
Let's restrict memfd backend to systems with sealing support.
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Message-Id: <20190311135850.6537-2-i.maximets@samsung.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
hostmem-file and hostmem-memfd use the whole object path for the
memory region name, and hostname-ram uses only the path component (the
object id, or canonical path basename):
qemu -m 1024 -object memory-backend-file,id=mem,size=1G,mem-path=/tmp/foo -numa node,memdev=mem -monitor stdio
(qemu) info ramblock
Block Name PSize Offset Used Total
/objects/mem 4 KiB 0x0000000000000000 0x0000000040000000 0x0000000040000000
qemu -m 1024 -object memory-backend-memfd,id=mem,size=1G -numa node,memdev=mem -monitor stdio
(qemu) info ramblock
Block Name PSize Offset Used Total
/objects/mem 4 KiB 0x0000000000000000 0x0000000040000000 0x0000000040000000
qemu -m 1024 -object memory-backend-ram,id=mem,size=1G -numa node,memdev=mem -monitor stdio
(qemu) info ramblock
Block Name PSize Offset Used Total
mem 4 KiB 0x0000000000000000 0x0000000040000000 0x0000000040000000
For consistency, change to use object id for -file and -memfd as well
with >= 4.0.
Having a consistent naming allows to migrate to different hostmem
backends.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Eduardo Habkost <ehabkost@redhat.com>
memfd_backend_memory_alloc/file_backend_memory_alloc both needlessly
are are calling host_memory_backend_mr_inited() which creates an
illusion that alloc could be called multiple times but it isn't, it's
called once from UserCreatable complete().
Suggested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The share=on/off property is used to modified mmap() MAP_SHARED
setting. Make it on by default for convenience and compatibility
reasons.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Run some memfd-related checks before registering hostmem-memfd &
various properties. This will help libvirt to figure out what the host
is supposed to be capable of.
qemu_memfd_check() is changed to a less optimized version, since it is
used with various flags, it no longer caches the result.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180906161415.8543-1-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add a new memory backend, similar to hostmem-file, except that it
doesn't need to create files. It also enforces memory sealing.
This backend is mainly useful for sharing the memory with other
processes.
Note that Linux supports transparent huge-pages of shmem/memfd memory
since 4.8. It is relatively easier to set up THP than a dedicate
hugepage mount point by using "madvise" in
/sys/kernel/mm/transparent_hugepage/shmem_enabled.
Since 4.14, memfd allows to set hugetlb requirement explicitly.
Pending for merge in 4.16 is memfd sealing support for hugetlb backed
memory.
Usage:
-object memory-backend-memfd,id=mem1,size=1G
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180201132757.23063-5-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
