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Subject[PATCH v2] docs: clarify KVM related kernel parameters' descriptions
Date
The descriptions of certain KVM related kernel parameters can be
confusing. They state "Disable ...," which may make people think that
setting them to 1 will disable the associated feature when in fact the
opposite is true.

This commit addresses this issue by revising the descriptions of these
parameters by using "Control..." rather than "Enable/Disable...".
1==enabled or 0==disabled can be communicated by the description of
default value such as "1 (enabled)" or "0 (disabled)".

Also update the description of KVM's default value for kvm-intel.nested
as it is enabled by default.

Signed-off-by: Yan-Jie Wang <yanjiewtw@gmail.com>
---
Changes in v2:
- Revise the descriptions based on Sean's suggesstion.
- Fix the wrong default value of kvm-intel.nested
---
.../admin-guide/kernel-parameters.txt | 53 ++++++++++---------
1 file changed, 29 insertions(+), 24 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9e5bab29685f..450c9d3af3ed 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2551,12 +2551,13 @@
If the value is 0 (the default), KVM will pick a period based
on the ratio, such that a page is zapped after 1 hour on average.

- kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
- Default is 1 (enabled)
+ kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
+ KVM/SVM. Default is 1 (enabled).

- kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
- for all guests.
- Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
+ kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
+ a.k.a. Two-Dimensional Page Tables. Default is 1
+ (enabled). Disable by KVM if hardware lacks support
+ for NPT.

kvm-arm.mode=
[KVM,ARM] Select one of KVM/arm64's modes of operation.
@@ -2602,30 +2603,33 @@
Format: <integer>
Default: 5

- kvm-intel.ept= [KVM,Intel] Disable extended page tables
- (virtualized MMU) support on capable Intel chips.
- Default is 1 (enabled)
+ kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
+ a.k.a. Two-Dimensional Page Tables. Default is 1
+ (enabled). Disable by KVM if hardware lacks support
+ for EPT.

kvm-intel.emulate_invalid_guest_state=
- [KVM,Intel] Disable emulation of invalid guest state.
- Ignored if kvm-intel.enable_unrestricted_guest=1, as
- guest state is never invalid for unrestricted guests.
- This param doesn't apply to nested guests (L2), as KVM
- never emulates invalid L2 guest state.
- Default is 1 (enabled)
+ [KVM,Intel] Control whether to emulate invalid guest
+ state. Ignored if kvm-intel.enable_unrestricted_guest=1,
+ as guest state is never invalid for unrestricted
+ guests. This param doesn't apply to nested guests (L2),
+ as KVM never emulates invalid L2 guest state.
+ Default is 1 (enabled).

kvm-intel.flexpriority=
- [KVM,Intel] Disable FlexPriority feature (TPR shadow).
- Default is 1 (enabled)
+ [KVM,Intel] Control KVM's use of FlexPriority feature
+ (TPR shadow). Default is 1 (enabled). Disalbe by KVM if
+ hardware lacks support for it.

kvm-intel.nested=
- [KVM,Intel] Enable VMX nesting (nVMX).
- Default is 0 (disabled)
+ [KVM,Intel] Control nested virtualization feature in
+ KVM/VMX. Default is 1 (enabled).

kvm-intel.unrestricted_guest=
- [KVM,Intel] Disable unrestricted guest feature
- (virtualized real and unpaged mode) on capable
- Intel chips. Default is 1 (enabled)
+ [KVM,Intel] Control KVM's use of unrestricted guest
+ feature (virtualized real and unpaged mode). Default
+ is 1 (enabled). Disable by KVM if EPT is disabled or
+ hardware lacks support for it.

kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
CVE-2018-3620.
@@ -2639,9 +2643,10 @@

Default is cond (do L1 cache flush in specific instances)

- kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
- feature (tagged TLBs) on capable Intel chips.
- Default is 1 (enabled)
+ kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
+ Identification feature (tagged TLBs). Default is 1
+ (enabled). Disable by KVM if hardware lacks support
+ for it.

l1d_flush= [X86,INTEL]
Control mitigation for L1D based snooping vulnerability.
base-commit: 865fdb08197e657c59e74a35fa32362b12397f58
--
2.34.1

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