Xen/mmapv3 #241

vireshk · 2023-06-23T08:07:48Z

Add support for Xen specific memory mapping

Xen allows two memory mapping mechanisms:

Foreign mapping: entire guest space is mapped at once.
Grant mapping: guest controls what backend is allowed to map.

Both these mechanisms required additional mapping support, for example
an ioctl() needs to be issued (with arguments passed from backend),
along with mmap().

Also for grant memory mapping, the mapping may or may not be done in
advance and may be required to be done on-demand.

Add memory mapping support for both these cases, under a new feature
"xen".

We can't use the existing as_ptr() API, as the memory may not be mapped
already. Mark the existing API available to non-xen implementations only.

Also add new implementations, ptr_guard() and ptr_guard_mut(), for both xen
and non-xen platforms, which can be used to map memory and then get a
pointer to it, work on it, and unmap the memory automatically.

This also adds few custom buidkite testcases to test Xen based implementation.

Signed-off-by: Viresh Kumar [email protected]

jiangliu · 2023-06-27T08:23:48Z

Really hope GrantTable is available for kvm too:)

jiangliu · 2023-06-27T08:27:53Z

README.md

+used for all tests in this crate.
+
+It was decided by the `rust-vmm` maintainers to keep the interface simple and
+build the crate for either standard Unix memory mapping or Xen, and not both.


vireshk · 2023-06-27T08:28:36Z

Really hope GrantTable is available for kvm too:)

:)

I haven't really followed the pKvm discussions, since it is going to be about secure guests, they will surely need something similar. Either something exactly like Xen, or they may fix the mappable areas somewhere (which may have penalties in form on no ZeroCopy).

roypat

Looks good! I didn't really look too deeply into the mmap_xen.rs code because I'm lacking Xen expertise, but everything else I'm happy with approving! It's just missing a Changelog entry for what's added (Xen support, the new API for accessing pointers to volatile slices is all I think?) and we should be good to go :)

src/volatile_memory.rs

Xen allows two memory mapping mechanisms: - Foreign mapping: entire guest space is mapped at once. - Grant mapping: guest controls what backend is allowed to map. Both these mechanisms required additional mapping support, for example an ioctl() needs to be issued (with arguments passed from backend), along with mmap(). Also for grant memory mapping, the mapping may or may not be done in advance and may be required to be done on-demand. Support for that will be added by a separate commit later. Add memory mapping support for both these cases, under a new feature "xen". Also add support to do generic Unix type mapping via Xen, in absence of foreign or grant mapping, which will be used by test code for other modules. Signed-off-by: Viresh Kumar <[email protected]>

vireshk · 2023-06-27T09:24:53Z

Looks good! I didn't really look too deeply into the mmap_xen.rs code because I'm lacking Xen expertise, but everything else I'm happy with approving! It's just missing a Changelog entry for what's added (Xen support, the new API for accessing pointers to volatile slices is all I think?) and we should be good to go :)

Thanks. I have updated the changelog and also added two documentation examples (for foreign and grant mappings) in Xen's MmapRegion::from_range() helper.

roypat · 2023-06-27T10:54:04Z

Looks good! I didn't really look too deeply into the mmap_xen.rs code because I'm lacking Xen expertise, but everything else I'm happy with approving! It's just missing a Changelog entry for what's added (Xen support, the new API for accessing pointers to volatile slices is all I think?) and we should be good to go :)

Thanks. I have updated the changelog and also added two documentation examples (for foreign and grant mappings) in Xen's MmapRegion::from_range() helper.

I think you might have forgotten to push the changes? 😅

vireshk · 2023-06-27T10:56:40Z

I think you might have forgotten to push the changes? sweat_smile

Maybe not :)

65f2c8d

roypat · 2023-06-27T11:01:08Z

I think you might have forgotten to push the changes? sweat_smile

Maybe not :)

65f2c8d

ah whoops missed that, so sorry! Am still not seeing the changelog though 🤔

vireshk · 2023-06-27T11:14:57Z

ah whoops missed that, so sorry! Am still not seeing the changelog though thinking

My mistake. I though you were asking me to update the Pull request's commit message :(, only now realized you meant CHANGELOG.md :)

Done now.

For Xen grant memory mapping model, the memory can't always be mapped in advance and it may be required to map it on the fly. This commit adds support for the same by introducing a new field for the various volatile memory structures: `mmap: Option<&'a MmapInfo>`. The type `MmapInfo` is set to `PhantomData<()>` for all the existing users, and is set to `MmapXen` for Xen. All the existing users set the new field to `None` and so the behavior remains unchanged for them. With Xen grant memory mappings, the address returned by as_ptr() will simply be an offset into the region, as the real mapping happens at a later point. In order not to break existing users of the API, lets keep the existing API around for non-xen implementations. Add new implementations, ptr_guard() and ptr_guard_mut(), for both xen and non-xen platforms, which can be used to map memory and then get a pointer to it, work on it, and unmap the memory automatically. Signed-off-by: Viresh Kumar <[email protected]>

Add a documentation examples for Xen specific mappings. They are built only for UNIX mapping type currently to make sure tests don't fail, but the documentation does show actual Xen code. Signed-off-by: Viresh Kumar <[email protected]>

Update README with implementation details of the Xen mapping model. Signed-off-by: Viresh Kumar <[email protected]>

Some of the custom tests are run with only "backend-mmap" feature enabled. Run them for "xen" as well. Some of the standard tests from rust-vmm-ci run with "--all-features" (which include "xen" too), add custom tests for those without the "xen" feature. Since the tests from rust-vmm-ci are named normally (without "xen" keyword), append non-xen tests with "-no-xen" to make those clear. Signed-off-by: Viresh Kumar <[email protected]>

Update CHANGELOG.md with latest updates. Signed-off-by: Viresh Kumar <[email protected]>

Update coverage score, based on new tests. Signed-off-by: Viresh Kumar <[email protected]>

Ablu · 2023-06-28T08:29:30Z

/me is still investigating some test failures with virtiofsd. May very likely be in my setup. Will report once I figured it out.

Ablu · 2023-06-28T09:21:28Z

Tested OK with virtiofsd + small patch [1] on Xen [2] with grant mappings [3] on 6.1 series kernel [4].

Errors were my own.

[1] https://gitlab.com/ablu/virtiofsd/-/commit/9466396862dde30f3b692c6e9eacbc89044eb874
[2] vireshk/xen@acb25f0
[3] virtio = [ "type=virtio,device26,transport=mmio,grant_usage=1" ]
[4] 6.1.24-yocto-standard

vireshk · 2023-06-28T09:52:18Z

Tested OK with virtiofsd + small patch [1] on Xen [2] with grant mappings [3] on 6.1 series kernel [4].

Thanks Erik.

vireshk requested review from alexandruag, bonzini, jiangliu and roypat as code owners June 23, 2023 08:07

vireshk mentioned this pull request Jun 23, 2023

Xen/mmapv2 #231

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vireshk force-pushed the xen/mmapv3 branch from dbbc53e to fa998d5 Compare June 23, 2023 08:23

vireshk mentioned this pull request Jun 26, 2023

Mmap/reorg #235

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vireshk force-pushed the xen/mmapv3 branch 3 times, most recently from bfe15ad to f521825 Compare June 26, 2023 11:30

jiangliu reviewed Jun 27, 2023

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vireshk force-pushed the xen/mmapv3 branch from 32989cb to a00db43 Compare June 27, 2023 09:19

vireshk force-pushed the xen/mmapv3 branch from a00db43 to e9eb5a0 Compare June 27, 2023 09:28

roypat mentioned this pull request Jun 27, 2023

New CI artifacts firecracker-microvm/firecracker#3890

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vireshk force-pushed the xen/mmapv3 branch from c482595 to b54babc Compare June 28, 2023 05:41

vireshk added 6 commits June 28, 2023 11:46

mmap_xen: Add xen specific documentation examples

f91fc9d

Add a documentation examples for Xen specific mappings. They are built only for UNIX mapping type currently to make sure tests don't fail, but the documentation does show actual Xen code. Signed-off-by: Viresh Kumar <[email protected]>

README: Update with Xen implementation details

4642115

Update README with implementation details of the Xen mapping model. Signed-off-by: Viresh Kumar <[email protected]>

CHANGELOG: Update with Xen changes for next release

2daae87

Update CHANGELOG.md with latest updates. Signed-off-by: Viresh Kumar <[email protected]>

Update coverage score

078c352

Update coverage score, based on new tests. Signed-off-by: Viresh Kumar <[email protected]>

vireshk force-pushed the xen/mmapv3 branch from b54babc to 078c352 Compare June 28, 2023 06:16

roypat approved these changes Jun 28, 2023

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Ablu approved these changes Jun 28, 2023

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jiangliu approved these changes Jun 28, 2023

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jiangliu merged commit a3cc708 into rust-vmm:main Jun 28, 2023

vireshk deleted the xen/mmapv3 branch June 28, 2023 15:45

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Xen/mmapv3 #241

Xen/mmapv3 #241

vireshk commented Jun 23, 2023 •

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jiangliu commented Jun 27, 2023

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Xen/mmapv3 #241

Xen/mmapv3 #241

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