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[virtio-mem] Add hotplug/hotunplug support with statically allocated memory region #5462

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@Manciukic Manciukic commented Oct 3, 2025 •
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TODO

Reason

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By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
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CONTRIBUTING.md.

PR Checklist

  • I have read and understand CONTRIBUTING.md.
  • I have run tools/devtool checkbuild --all to verify that the PR passes
    build checks on all supported architectures.
  • I have run tools/devtool checkstyle to verify that the PR passes the
    automated style checks.
  • I have described what is done in these changes, why they are needed, and
    how they are solving the problem in a clear and encompassing way.
  • I have updated any relevant documentation (both in code and in the docs)
    in the PR.
  • I have mentioned all user-facing changes in CHANGELOG.md.
  • If a specific issue led to this PR, this PR closes the issue.
  • When making API changes, I have followed the
    Runbook for Firecracker API changes.
  • I have tested all new and changed functionalities in unit tests and/or
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  • This functionality cannot be added in rust-vmm.

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codecov bot commented Oct 3, 2025 •
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Codecov Report

❌ Patch coverage is 91.90871% with 39 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.11%. Comparing base (dab0533) to head (370eb4e).

Files with missing lines Patch % Lines
src/vmm/src/devices/virtio/mem/device.rs 95.88% 11 Missing ⚠️
src/vmm/src/lib.rs 0.00% 7 Missing ⚠️
src/vmm/src/rpc_interface.rs 0.00% 7 Missing ⚠️
src/vmm/src/devices/virtio/mem/request.rs 95.20% 6 Missing ⚠️
src/vmm/src/builder.rs 58.33% 5 Missing ⚠️
src/firecracker/src/api_server/parsed_request.rs 0.00% 2 Missing ⚠️
src/vmm/src/devices/virtio/mem/persist.rs 88.88% 1 Missing ⚠️
Additional details and impacted files 
@@                  Coverage Diff                   @@
##           feature/virtio-mem    #5462      +/-   ##
======================================================
+ Coverage               82.70%   83.11%   +0.41%     
======================================================
  Files                     270      271       +1     
  Lines                   27850    28315     +465     
======================================================
+ Hits                    23033    23534     +501     
+ Misses                   4817     4781      -36
Flag Coverage Δ
5.10-m5n.metal 83.31% <91.90%> (+0.45%) ⬆️
5.10-m6a.metal 82.60% <91.90%> (+0.48%) ⬆️
5.10-m6g.metal 80.00% <91.90%> (+0.47%) ⬆️
5.10-m6i.metal 83.30% <91.90%> (+0.45%) ⬆️
5.10-m7a.metal-48xl 82.59% <91.90%> (+0.48%) ⬆️
5.10-m7g.metal 80.01% <91.90%> (+0.48%) ⬆️
5.10-m7i.metal-24xl 83.27% <91.90%> (+0.44%) ⬆️
5.10-m7i.metal-48xl 83.28% <91.90%> (+0.45%) ⬆️
5.10-m8g.metal-24xl 80.00% <91.90%> (+0.46%) ⬆️
5.10-m8g.metal-48xl 80.00% <91.90%> (+0.47%) ⬆️
6.1-m5n.metal 83.34% <91.90%> (+0.46%) ⬆️
6.1-m6a.metal 82.63% <91.90%> (+0.48%) ⬆️
6.1-m6g.metal 80.00% <91.90%> (+0.47%) ⬆️
6.1-m6i.metal 83.33% <91.90%> (+0.45%) ⬆️
6.1-m7a.metal-48xl 82.62% <91.90%> (+0.48%) ⬆️
6.1-m7g.metal 80.00% <91.90%> (+0.47%) ⬆️
6.1-m7i.metal-24xl 83.35% <91.90%> (+0.46%) ⬆️
6.1-m7i.metal-48xl 83.35% <91.90%> (+0.45%) ⬆️
6.1-m8g.metal-24xl 80.00% <91.90%> (+0.47%) ⬆️
6.1-m8g.metal-48xl 80.00% <91.90%> (+0.47%) ⬆️

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Manciukic added 14 commits October 6, 2025 17:49
@Manciukic
feat(virtio-mem): add static allocation of hotpluggable memory
5377a55 
Allocate the memory that will be used for hotplugging. Initially, this
memory will be registered with KVM, but that will change later when we
add dynamic slot support.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
feat(virtio-mem): wire PATCH support
c324adc 
Wire up PATCH requests with the virtio-mem device.
All the validation is performed in the device, but the actual operation
is not yet implemented.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
doc(virtio-mem): document PATCH API in swagger and docs
b2f0cfc 
Add entry for the patch API in Swagger and in the docs.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
test(virtio-mem): add API tests for PATCH
84c7db5 
Test that the new PATCH API behaves as expected.
Also updates expected metrics and fixes memory monitor to account for
hotplugging.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
feat(virtio-mem): add virtio request parsing and dummy response
1425c7c 
Parse virtio requests over the queue and always ack them. Following
commits will add the state management inside the device.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
feat(virtio-mem): implement virtio requests
a1ae2ca 
This commit adds block state management and implements the virtio
requests for the virtio-mem device.

Block state is tracked using a BitVec, each bit representing a single
block.

Plug/Unplug requests are validated before being executed to verify the
range is valid (aligned and within range), and that all blocks in range
are unplugged/plugged, as per the virtio spec.

UplugAll is the only request where usable_region_size can be lowered.

This commit is missing the dynamic KVM slot management which will be
added later.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
test(virtio-mem): add unit tests for virtio queue request handling
adcdddb 
Adds unit tests using VirtioTestHelper to verify correct functioning of
the new device.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
test(metrics): add virtio-mem device metrics to validation
0c8c045 
Add the virtio-mem device metrics to the integ test validation.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
fix(examples/uffd): unregister range on UFFD Remove event
d4b0f9a 
If the handler receives a UFFD remove event, it currently stores the PFN
and will reply with a zero page whenever it receives a pagefault event
for that page.
This works well with 4k pages, but zeropage is not supported on
hugepages. In order to support hugepages, let's just unregister from
UFFD whenever we get a remove event. By doing so, the handler won't
receive a notification for the removed page, and the VM will get a new
zero page from the kernel.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
feat(test/balloon): include HugePages in RSS measurements
9efa1b9 
This moves the logic to measure RSS to framework.utils and adds a logic
to also include huge pages in the measurement.

Furthermore, this also adds caching for the firecracker_pid, as well as
a new property to get the corresponding psutil.Process.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
refactor(test/balloon): move logic to get guest avail mem to framework
9b27bcf 
Move the logic to get the MemAvailable from /proc/meminfo inside the
guest to a new guest_stats module in the test framework. This provides a
new class MeminfoGuest that can be used to retrieve this information
(and more!).

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
test(virtio-mem): add functional integration tests for device
9fca25d 
Add integration tests for the new device:
 - check that the device is detected
 - check that hotplugging and unplugging works
 - check that memory can be used after hotplugging
 - check that memory is freed on hotunplug
 - check different config combinations
 - check different uvm types
 - check that contents are preserved across snapshot-restore

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
chore(test/virtio-mem): move tests under performance
2069fc3 
Since these tests need to be run on an ag=1 host, move them under the
"performance" folder.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic
test(virtio-mem): add rust integration tests
370eb4e 
These tests add unit test coverage to the builder.rs and vm.rs files
which where previously untested in the memory hotplug case.

Signed-off-by: Riccardo Mancini <[email protected]>
@Manciukic Manciukic force-pushed the virtio-mem/patch-api branch from c507d69 to 370eb4e Compare October 6, 2025 16:50
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