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Hint on cr3 update

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Remzi Arpaci-Dusseau
2018-03-11 21:26:44 -05:00
parent 88670897d8
commit 75a96baf8f
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vm-xv6-intro/README.md
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@@ -69,6 +69,13 @@ or `addr` points to a region that is not currently a part of the address
space, or `len` is less than or equal to zero, return -1 and do not change space, or `len` is less than or equal to zero, return -1 and do not change
anything. Otherwise, return 0 upon success. anything. Otherwise, return 0 upon success.
Hint: after changing a page-table entry, you need to make sure the hardware
knows of the change. On 32-bit x86, this is readily accomplished by updating
the `CR3` register (what we generically call the *page-table base register* in
class). When the hardware sees that you overwrote `CR3` (even with the same
value), it guarantees that your PTE updates will be used upon subsequent
accesses. The `lcr3()` function will help you in this pursuit.
## Handling Illegal Accesses ## Handling Illegal Accesses
In both the cases above, you should be able to demonstrate what happens when In both the cases above, you should be able to demonstrate what happens when