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| -rw-r--r-- | Documentation/kvm/mmu.txt | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/Documentation/kvm/mmu.txt b/Documentation/kvm/mmu.txt index 2201dcba92a1..1e7ecdd15bba 100644 --- a/Documentation/kvm/mmu.txt +++ b/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 =============== |