This supports virtio-mem-pci device on "virt" platform, by simply
following the implementation on x86.
* This implements the hotplug handlers to support virtio-mem-pci
device hot-add, while the hot-remove isn't supported as we have
on x86.
* The block size is 512MB on ARM64 instead of 128MB on x86.
* It has been passing the tests with various combinations like 64KB
and 4KB page sizes on host and guest, different memory device
backends like normal, transparent huge page and HugeTLB, plus
migration.
Co-developed-by: David Hildenbrand <david@redhat.com>
Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-id: 20220111063329.74447-3-gshan@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
The default block size is same as to the THP size, which is either
retrieved from "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
or hardcoded to 2MB. There are flaws in both mechanisms and this
intends to fix them up.
* When "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size" is
used to getting the THP size, 32MB and 512MB are valid values
when we have 16KB and 64KB page size on ARM64.
* When the hardcoded THP size is used, 2MB, 32MB and 512MB are
valid values when we have 4KB, 16KB and 64KB page sizes on
ARM64.
Co-developed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-id: 20220111063329.74447-2-gshan@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Set the new default to "auto", keeping it set to "off" for compat
machines. This property is only available for x86 targets.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20211217134039.29670-4-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
With VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, we signal the VM that reading
unplugged memory is not supported. We have to fail feature negotiation
in case the guest does not support VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE.
First, VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE is required to properly handle
memory backends (or architectures) without support for the shared zeropage
in the hypervisor cleanly. Without the shared zeropage, even reading an
unpopulated virtual memory location can populate real memory and
consequently consume memory in the hypervisor. We have a guaranteed shared
zeropage only on MAP_PRIVATE anonymous memory.
Second, we want VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE to be the default
long-term as even populating the shared zeropage can be problematic: for
example, without THP support (possible) or without support for the shared
huge zeropage with THP (unlikely), the PTE page tables to hold the shared
zeropage entries can consume quite some memory that cannot be reclaimed
easily.
Third, there are other optimizations+features (e.g., protection of
unplugged memory, reducing the total memory slot size and bitmap sizes)
that will require VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE.
We really only support x86 targets with virtio-mem for now (and
Linux similarly only support x86), but that might change soon, so prepare
for different targets already.
Add a new "unplugged-inaccessible" tristate property for x86 targets:
- "off" will keep VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE unset and legacy
guests working.
- "on" will set VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE and stop legacy guests
from using the device.
- "auto" selects the default based on support for the shared zeropage.
Warn in case the property is set to "off" and we don't have support for the
shared zeropage.
For existing compat machines, the property will default to "off", to
not change the behavior but eventually warn about a problematic setup.
Short-term, we'll set the property default to "auto" for new QEMU machines.
Mid-term, we'll set the property default to "on" for new QEMU machines.
Long-term, we'll deprecate the parameter and disallow legacy
guests completely.
The property has to match on the migration source and destination. "auto"
will result in the same VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE setting as long
as the qemu command line (esp. memdev) match -- so "auto" is good enough
for migration purposes and the parameter doesn't have to be migrated
explicitly.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20211217134039.29670-3-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
For scarce memory resources, such as hugetlb, we want to be able to
prealloc such memory resources in order to not crash later on access. On
simple user errors we could otherwise easily run out of memory resources
an crash the VM -- pretty much undesired.
For ordinary memory devices, such as DIMMs, we preallocate memory via the
memory backend for such use cases; however, with virtio-mem we're dealing
with sparse memory backends; preallocating the whole memory backend
destroys the whole purpose of virtio-mem.
Instead, we want to preallocate memory when actually exposing memory to the
VM dynamically, and fail plugging memory gracefully + warn the user in case
preallocation fails.
A common use case for hugetlb will be using "reserve=off,prealloc=off" for
the memory backend and "prealloc=on" for the virtio-mem device. This
way, no huge pages will be reserved for the process, but we can recover
if there are no actual huge pages when plugging memory. Libvirt is
already prepared for this.
Note that preallocation cannot protect from the OOM killer -- which
holds true for any kind of preallocation in QEMU. It's primarily useful
only for scarce memory resources such as hugetlb, or shared file-backed
memory. It's of little use for ordinary anonymous memory that can be
swapped, KSM merged, ... but we won't forbid it.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20211217134611.31172-9-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
If we warn about the block size being smaller than the default, we skip
some alignment checks.
This can currently only fail on x86-64, when specifying a block size of
1 MiB, however, we detect the THP size of 2 MiB.
Fixes: 228957fea3 ("virtio-mem: Probe THP size to determine default block size")
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20211011173305.13778-1-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Migration code now properly handles RAMBlocks which are indirectly managed
by a RamDiscardManager. No need for manual handling via the free page
optimization interface, let's get rid of it.
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Implement it similar to the replay_populated callback.
Acked-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
We implement the RamDiscardManager interface and only require coordinated
discarding of RAM to work.
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210413095531.25603-13-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
vIOMMU support works already with RamDiscardManager as long as guests only
map populated memory. Both, populated and discarded memory is mapped
into &address_space_memory, where vfio_get_xlat_addr() will find that
memory, to create the vfio mapping.
Sane guests will never map discarded memory (e.g., unplugged memory
blocks in virtio-mem) into an IOMMU - or keep it mapped into an IOMMU while
memory is getting discarded. However, there are two cases where a malicious
guests could trigger pinning of more memory than intended.
One case is easy to handle: the guest trying to map discarded memory
into an IOMMU.
The other case is harder to handle: the guest keeping memory mapped in
the IOMMU while it is getting discarded. We would have to walk over all
mappings when discarding memory and identify if any mapping would be a
violation. Let's keep it simple for now and print a warning, indicating
that setting RLIMIT_MEMLOCK can mitigate such attacks.
We have to take care of incoming migration: at the point the
IOMMUs get restored and start creating mappings in vfio, RamDiscardManager
implementations might not be back up and running yet: let's add runstate
priorities to enforce the order when restoring.
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210413095531.25603-10-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Let's properly notify when (un)plugging blocks, after discarding memory
and before allowing the guest to consume memory. Handle errors from
notifiers gracefully (e.g., no remaining VFIO mappings) when plugging,
rolling back the change and telling the guest that the VM is busy.
One special case to take care of is replaying all notifications after
restoring the vmstate. The device starts out with all memory discarded,
so after loading the vmstate, we have to notify about all plugged
blocks.
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210413095531.25603-6-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Any errors are unexpected and ram_block_discard_range() already properly
prints errors. Let's stop manually reporting errors.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210413095531.25603-5-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Let's factor out the core logic, no need to replicate.
Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210413095531.25603-4-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
The bulk stage is kind of weird: migration_bitmap_find_dirty() will
indicate a dirty page, however, ram_save_host_page() will never save it, as
migration_bitmap_clear_dirty() detects that it is not dirty.
We already fill the bitmap in ram_list_init_bitmaps() with ones, marking
everything dirty - it didn't used to be that way, which is why we needed
an explicit first bulk stage.
Let's simplify: make the bitmap the single source of thuth. Explicitly
handle the "xbzrle_enabled after first round" case.
Regarding XBZRLE (implicitly handled via "ram_bulk_stage = false" right
now), there is now a slight change in behavior:
- Colo: When starting, it will be disabled (was implicitly enabled)
until the first round actually finishes.
- Free page hinting: When starting, XBZRLE will be disabled (was implicitly
enabled) until the first round actually finished.
- Snapshots: When starting, XBZRLE will be disabled. We essentially only
do a single run, so I guess it will never actually get disabled.
Postcopy seems to indirectly disable it in ram_save_page(), so there
shouldn't be really any change.
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210216105039.40680-1-david@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Let's allow a minimum block size of 1 MiB in all configurations. Select
the default block size based on
- The page size of the memory backend.
- The THP size if the memory backend size corresponds to the real host
page size.
- The global minimum of 1 MiB.
and warn if something smaller is configured by the user.
VIRTIO_MEM only supports Linux (depends on LINUX), so we can probe the
THP size unconditionally.
For now we only support virtio-mem on x86-64 - there isn't a user-visible
change (x86-64 only supports 2 MiB THP on the PMD level) - the default
was, and will be 2 MiB.
If we ever have THP on the PUD level (e.g., 1 GiB THP on x86-64), we
expect it to be more transparent - e.g., to only optimize fully populated
ranges unless explicitly told /configured otherwise (in contrast to PMD
THP).
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20201008083029.9504-4-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
The spec states:
"The device MUST set addr, region_size, usable_region_size, plugged_size,
requested_size to multiples of block_size."
With block sizes > 256MB, we currently wouldn't guarantee that for the
usable_region_size.
Note that we cannot exceed the region_size, as we already enforce the
alignment there properly.
Fixes: 910b25766b ("virtio-mem: Paravirtualized memory hot(un)plug")
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20201008083029.9504-3-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
The spec states:
"The device MUST set addr, region_size, usable_region_size, plugged_size,
requested_size to multiples of block_size."
In some cases, we currently don't guarantee that for "addr": For example,
when starting a VM with 4 GiB boot memory and a virtio-mem device with a
block size of 2 GiB, "memaddr"/"addr" will be auto-assigned to
0x140000000 (5 GiB).
We'll try to improve auto-assignment for memory devices next, to avoid
bailing out in case memory device code selects a bad address.
Note: The Linux driver doesn't support such big block sizes yet.
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Fixes: 910b25766b ("virtio-mem: Paravirtualized memory hot(un)plug")
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20201008083029.9504-2-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
If error occurs while processing the virtio request we should call
'virtqueue_detach_element' to detach the element from the virtqueue
before free the elem.
Signed-off-by: Li Qiang <liq3ea@163.com>
Message-Id: <20200816142245.17556-1-liq3ea@163.com>
Fixes: 910b25766b ("virtio-mem: Paravirtualized memory hot(un)plug")
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This likely affects other, less popular host architectures as well.
Less common host architectures under linux get QEMU_VMALLOC_ALIGN (from
which VIRTIO_MEM_MIN_BLOCK_SIZE is derived) define to a variable of
type uintptr, which isn't compatible with the format specifier used to
print a user message. Since this particular usage of the underlying data
seems unique to this file, the simple fix is to just cast
QEMU_VMALLOC_ALIGN to uint32_t, which corresponds to the format specifier
used.
Signed-off-by: Bruce Rogers <brogers@suse.com>
Message-Id: <20200730130519.168475-1-brogers@suse.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
object_get_canonical_path_component() returns a malloced copy of a
property name on success, null on failure.
19 of its 25 callers immediately free the returned copy.
Change object_get_canonical_path_component() to return the property
name directly. Since modifying the name would be wrong, adjust the
return type to const char *.
Drop the free from the 19 callers become simpler, add the g_strdup()
to the other six.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200714160202.3121879-4-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
The content of unplugged memory is undefined and should not be migrated,
ever. Exclude all unplugged memory during precopy using the precopy notifier
infrastructure introduced for free page hinting in virtio-balloon.
Unplugged memory is marked as "not dirty", meaning it won't be
considered for migration.
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-21-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Let's add some trace events that might come in handy later.
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-20-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
We want to make sure that certain properties don't change during
migration, especially to catch user errors in a nice way. Let's migrate
a temporary structure and validate that the properties didn't change.
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-19-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
We want to send qapi events in case the size of a virtio-mem device
changes. This allows upper layers to always know how much memory is
actually currently consumed via a virtio-mem device.
Unfortuantely, we have to report the id of our proxy device. Let's provide
an easy way for our proxy device to register, so it can send the qapi
events. Piggy-backing on the notifier infrastructure (although we'll
only ever have one notifier registered) seems to be an easy way.
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-17-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This is the very basic/initial version of virtio-mem. An introduction to
virtio-mem can be found in the Linux kernel driver [1]. While it can be
used in the current state for hotplug of a smaller amount of memory, it
will heavily benefit from resizeable memory regions in the future.
Each virtio-mem device manages a memory region (provided via a memory
backend). After requested by the hypervisor ("requested-size"), the
guest can try to plug/unplug blocks of memory within that region, in order
to reach the requested size. Initially, and after a reboot, all memory is
unplugged (except in special cases - reboot during postcopy).
The guest may only try to plug/unplug blocks of memory within the usable
region size. The usable region size is a little bigger than the
requested size, to give the device driver some flexibility. The usable
region size will only grow, except on reboots or when all memory is
requested to get unplugged. The guest can never plug more memory than
requested. Unplugged memory will get zapped/discarded, similar to in a
balloon device.
The block size is variable, however, it is always chosen in a way such that
THP splits are avoided (e.g., 2MB). The state of each block
(plugged/unplugged) is tracked in a bitmap.
As virtio-mem devices (e.g., virtio-mem-pci) will be memory devices, we now
expose "VirtioMEMDeviceInfo" via "query-memory-devices".
--------------------------------------------------------------------------
There are two important follow-up items that are in the works:
1. Resizeable memory regions: Use resizeable allocations/RAM blocks to
grow/shrink along with the usable region size. This avoids creating
initially very big VMAs, RAM blocks, and KVM slots.
2. Protection of unplugged memory: Make sure the gust cannot actually
make use of unplugged memory.
Other follow-up items that are in the works:
1. Exclude unplugged memory during migration (via precopy notifier).
2. Handle remapping of memory.
3. Support for other architectures.
--------------------------------------------------------------------------
Example usage (virtio-mem-pci is introduced in follow-up patches):
Start QEMU with two virtio-mem devices (one per NUMA node):
$ qemu-system-x86_64 -m 4G,maxmem=20G \
-smp sockets=2,cores=2 \
-numa node,nodeid=0,cpus=0-1 -numa node,nodeid=1,cpus=2-3 \
[...]
-object memory-backend-ram,id=mem0,size=8G \
-device virtio-mem-pci,id=vm0,memdev=mem0,node=0,requested-size=0M \
-object memory-backend-ram,id=mem1,size=8G \
-device virtio-mem-pci,id=vm1,memdev=mem1,node=1,requested-size=1G
Query the configuration:
(qemu) info memory-devices
Memory device [virtio-mem]: "vm0"
memaddr: 0x140000000
node: 0
requested-size: 0
size: 0
max-size: 8589934592
block-size: 2097152
memdev: /objects/mem0
Memory device [virtio-mem]: "vm1"
memaddr: 0x340000000
node: 1
requested-size: 1073741824
size: 1073741824
max-size: 8589934592
block-size: 2097152
memdev: /objects/mem1
Add some memory to node 0:
(qemu) qom-set vm0 requested-size 500M
Remove some memory from node 1:
(qemu) qom-set vm1 requested-size 200M
Query the configuration again:
(qemu) info memory-devices
Memory device [virtio-mem]: "vm0"
memaddr: 0x140000000
node: 0
requested-size: 524288000
size: 524288000
max-size: 8589934592
block-size: 2097152
memdev: /objects/mem0
Memory device [virtio-mem]: "vm1"
memaddr: 0x340000000
node: 1
requested-size: 209715200
size: 209715200
max-size: 8589934592
block-size: 2097152
memdev: /objects/mem1
[1] https://lkml.kernel.org/r/20200311171422.10484-1-david@redhat.com
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-11-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
