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-rw-r--r--Documentation/virtual/kvm/mmu.txt18
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
index f46aa58..5dc972c 100644
--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -165,6 +165,10 @@ Shadow pages contain the following information:
Contains the value of efer.nxe for which the page is valid.
role.cr0_wp:
Contains the value of cr0.wp for which the page is valid.
+ role.smep_andnot_wp:
+ Contains the value of cr4.smep && !cr0.wp for which the page is valid
+ (pages for which this is true are different from other pages; see the
+ treatment of cr0.wp=0 below).
gfn:
Either the guest page table containing the translations shadowed by this
page, or the base page frame for linear translations. See role.direct.
@@ -317,6 +321,20 @@ on fault type:
(user write faults generate a #PF)
+In the first case there is an additional complication if CR4.SMEP is
+enabled: since we've turned the page into a kernel page, the kernel may now
+execute it. We handle this by also setting spte.nx. If we get a user
+fetch or read fault, we'll change spte.u=1 and spte.nx=gpte.nx back.
+
+To prevent an spte that was converted into a kernel page with cr0.wp=0
+from being written by the kernel after cr0.wp has changed to 1, we make
+the value of cr0.wp part of the page role. This means that an spte created
+with one value of cr0.wp cannot be used when cr0.wp has a different value -
+it will simply be missed by the shadow page lookup code. A similar issue
+exists when an spte created with cr0.wp=0 and cr4.smep=0 is used after
+changing cr4.smep to 1. To avoid this, the value of !cr0.wp && cr4.smep
+is also made a part of the page role.
+
Large pages
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