diff options
Diffstat (limited to 'Documentation/virtual')
| -rw-r--r-- | Documentation/virtual/kvm/mmu.txt | 18 |
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 =========== |