---

yaml
---
r: 202307
b: refs/heads/master
c: ec87fe2
h: refs/heads/master
i:
  202305: 32568f6
  202303: 8dc147c
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 8184dd38e22fcaec664c2b98c382b85c26780e26
+refs/heads/master: ec87fe2afcbcc4f430554980ec3e408bae34229d

trunk/Documentation/kvm/mmu.txt

@@ -298,6 +298,25 @@ Host translation updates:
   - look up affected sptes through reverse map
   - drop (or update) translations
 
+Emulating cr0.wp
+================
+
+If tdp is not enabled, the host must keep cr0.wp=1 so page write protection
+works for the guest kernel, not guest guest userspace.  When the guest
+cr0.wp=1, this does not present a problem.  However when the guest cr0.wp=0,
+we cannot map the permissions for gpte.u=1, gpte.w=0 to any spte (the
+semantics require allowing any guest kernel access plus user read access).
+
+We handle this by mapping the permissions to two possible sptes, depending
+on fault type:
+
+- kernel write fault: spte.u=0, spte.w=1 (allows full kernel access,
+  disallows user access)
+- read fault: spte.u=1, spte.w=0 (allows full read access, disallows kernel
+  write access)
+
+(user write faults generate a #PF)
+
 Further reading
 ===============