add Mapper::clear to clear any page table entry regardless of present flag

[Wasabi375]

Add a way to clear page table entries that don't have the present flag set.

See #481 for an explanation

fixes: #481

[Freax13]

Thank you for your contribution!

[Wasabi375]

Looks like cargo doc is still failing. I should have a fix for that shortly

[Wasabi375]

I merged my commits and also added a changelog entry. Let me know if there is anything else I should do.

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I noticed that unmap and now clear are both safe functions. Shouldn't they be marked as unsafe? After all using unmap or clear can invalidate any existing reference and rust safety guarantees require all references to be valid?
In any case that should probably be a second PR/issue

[Freax13]

I noticed that unmap and now clear are both safe functions. Shouldn't they be marked as unsafe? After all using unmap or clear can invalidate any existing reference and rust safety guarantees require all references to be valid? In any case that should probably be a second PR/issue

We don't consider page faults to be UB so unmapping memory by itself isn't unsafe.

[Wasabi375]

I noticed that unmap and now clear are both safe functions. Shouldn't they be marked as unsafe? After all using unmap or clear can invalidate any existing reference and rust safety guarantees require all references to be valid? In any case that should probably be a second PR/issue

We don't consider page faults to be UB so unmapping memory by itself isn't unsafe.

I'm not sure i agree with that, but it doesn't matter for this pr anyways

[Freax13]

I noticed that unmap and now clear are both safe functions. Shouldn't they be marked as unsafe? After all using unmap or clear can invalidate any existing reference and rust safety guarantees require all references to be valid? In any case that should probably be a second PR/issue

We don't consider page faults to be UB so unmapping memory by itself isn't unsafe.

I'm not sure i agree with that, but it doesn't matter for this pr anyways

Feel free to open an issue, if you want to discuss this more!

[Freax13]

Looks good to me, thank you again for your contribution!

[Freax13]

Recently, the clippy CI job got broken again by new lints in nightly, so I'll temporarily disable the merge requirement for that job to merge this PR.