Fix missing TLB flush

[sangho2]

This PR fixes missing TLB flushes. In particular, it covers cases like cross-core kernel-page not-present -> present or PDE widening, which result in faults because we do not maintain VM areas for kernel address space such that a page fault handler cannot properly update the PTEs. This PR simply flushes corresponding TLB entries.

[github-actions]

🤖 SemverChecks 🤖 No breaking API changes detected

Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.

[CvvT]

This PR fixes missing TLB flushes. In particular, it covers not-present -> present cases which suffer from corner cases like speculative page table walks and more.

If it's not-present --> present, my understanding is that in worst case CPU would trigger page fault. Once it's resolved, TLB would be updated. So, we don't need to flush TLB proactively.

[sangho2]

This PR fixes missing TLB flushes. In particular, it covers not-present -> present cases which suffer from corner cases like speculative page table walks and more.

If it's not-present --> present, my understanding is that in worst case CPU would trigger page fault. Once it's resolved, TLB would be updated. So, we don't need to flush TLB proactively.

There are some corner cases that I can reproduce and that's why I wrote this PR :)

[CvvT]

This PR fixes missing TLB flushes. In particular, it covers not-present -> present cases which suffer from corner cases like speculative page table walks and more.

If it's not-present --> present, my understanding is that in worst case CPU would trigger page fault. Once it's resolved, TLB would be updated. So, we don't need to flush TLB proactively.

There are some corner cases that I can reproduce and that's why I wrote this PR :)

What is the corner case?

[sangho2]

This PR fixes missing TLB flushes. In particular, it covers not-present -> present cases which suffer from corner cases like speculative page table walks and more.

If it's not-present --> present, my understanding is that in worst case CPU would trigger page fault. Once it's resolved, TLB would be updated. So, we don't need to flush TLB proactively.

There are some corner cases that I can reproduce and that's why I wrote this PR :)

What is the corner case?

This is about a kernel-level page fault. we don't have demand paging / page fault handler for it.