Re: [PATCH] munmap sealed memory cause memory to split (bug)

On Thu, Oct 17, 2024 at 10:46:10AM +0100, Lorenzo Stoakes wrote: [snip]

Anyway, let's try to decode (please take this as input as to how you should try to communicate these things):

So we start with a VMA like this:

012345678901 xxxxxxxxxxxx

We then seal the middle, starting at offset 4:

012345678901 xxxx****xxxx

This sets the VM_SEALED flag in the middle and splits VMAs resulting in 3 VMAs.

We then attempt to unmap 4 pages from offset 2, but this fails, as expected.

012345678901 xxxx****xxxx |--| fail

We then attempt to unmap 4 pages from offset 6, but this fails, as expected.

012345678901 xxxx****xxxx |--| fail

At each stage we should observe 4 VMAs.

CORRECTION: 3 VMAs.

[snip]