Specify meaning of R/W/X bits in PTE

1 files changed, 13 insertions, 0 deletions

diff --git a/src/supervisor.tex b/src/supervisor.tex
index d10cf0a..3bd0c8b 100644
--- a/src/supervisor.tex
+++ b/src/supervisor.tex
@@ -1119,6 +1119,19 @@ X & W & R & Meaning \\
 \label{pteperm}
 \end{table*}
 
+Attempting to fetch an instruction from a page that does not have execute
+permissions raises a fetch page-fault exception.  Attempting to execute
+a load or load-reserved instruction whose effective address lies within
+a page without read permissions raises a load page-fault exception.
+Attempting to execute a store, store-conditional (regardless of success),
+or AMO instruction whose effective address lies within a page without
+write permissions raises a store page-fault exception.
+\begin{commentary}
+AMOs never raise load page-fault exceptions.  Since any unreadable page is
+also unwritable, attempting to perform an AMO on an unreadable page always
+raises a store page-fault exception.
+\end{commentary}
+
 The U bit indicates whether the page is accessible to user mode.
 U-mode software may only access the page when U=1.  If the SUM bit
 in the {\tt sstatus} register is