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Subject[PATCH 2/2] KVM: MMU: document smap_andnot_wp
Date
Document this new role field

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
---
Documentation/virtual/kvm/mmu.txt | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
index 53838d9..c59bd9b 100644
--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -169,6 +169,10 @@ Shadow pages contain the following information:
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).
+ role.smap_andnot_wp:
+ Contains the value of cr4.smap && !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.
@@ -344,10 +348,16 @@ 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.
+In the first case there are two additional complications:
+- 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.
+- if CR4.SMAP is disabled: since the page has been changed to a kernel
+ page, it can not be reused when CR4.SMAP is enabled. We set
+ CR4.SMAP && !CR0.WP into shadow page's role to avoid this case. Note,
+ here we do not care the case that CR4.SMAP is enabled since KVM will
+ directly inject #PF to guest due to failed permission check.

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
--
2.1.0


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