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SubjectRe: pre12 VM doubts and patch

On Thu, 20 Sep 2001, Andrea Arcangeli wrote:
>
> when the page is exclusive we definitely can write to it

NO!

If it is a read-only mapping, we must NOT mark it writable.

The fact is, the page may have been written to earlier, marked read-only
with mprotect(), and the page is dirty but read-only, and swapping it in
MUST NOT markt it writable even if it is our last exclusive copy.

Which we've gotten wrong for a long time, actually. But you #if 0'ed the
fix that happened fairly recently.

Linus

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