Writes should only be allowed on already dirty translations.

[snue]

The code in https://github.com/blitz/vmmu/blob/master/libvmmu/src/tlb_entry.cpp#L20 should reject writes to translations that are not marked dirty.

The current implementation emulates the hardware behavior only, which does not specifically care for the dirty bit checks.

Currently, a translation obtained for a read will transparently allow later writes without causing a page walk (and thus not marking the page structures dirty). This is a bug.

Something along these lines after the mode == paging_mode::PHYS check should be sufficient:

        // Writes are only allowed on already dirty translations.
        if (op.is_write() and not attr().is_d())
            return false;

[snue]

Note that this change would break the current page walk logic, which does the allows() check before marking the entry dirty: https://github.com/blitz/vmmu/blob/master/libvmmu/src/pt_walk.cpp#L132-L133