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Message-ID: <ZFFEgptZg1P367F7@google.com>
Date: Tue, 2 May 2023 10:12:34 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Yan-Jie Wang <yanjiewtw@...il.com>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
Jonathan Corbet <corbet@....net>,
Paolo Bonzini <pbonzini@...hat.com>,
Randy Dunlap <rdunlap@...radead.org>,
Andre Przywara <andre.przywara@....com>,
Avi Kivity <avi@...hat.com>,
Ching-Chun Huang <jserv@...s.ncku.edu.tw>, trivial@...nel.org,
kvm@...r.kernel.org
Subject: Re: [PATCH] docs: clarify KVM related kernel parameters' descriptions
On Tue, May 02, 2023, Yan-Jie Wang wrote:
> The descriptions of certain KVM related kernel parameters can be
> ambiguous and confusing. They state 'Disable ...,' which implies that
> setting them to 1 would disable the associated features or options,
> when in fact the opposite is true.
>
> This commit addresses this issue by revising the descriptions of these
> parameters to make their intended behavior clear.
Less wrong perhaps, but IMO the actual behavior is still not captured, and from
a certain perspective the existing "Disable" verbiage better reflects how/when
most users would actually want to explicitly set a param.
Rather than commit one way or the other, what about reworking the descriptions
using this as a template? E.g. state that the param controls something, state
the default and use that to communicate that 1==enabled, and then, when appropriate,
clarify that KVM disables (or in some cases ignores) params if hardware doesn't
support the related feature(s).
kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
a.k.a. Two-Dimensional Page Tables. Default is 1
(enabled). Disabled by KVM if hardware lacks support
for EPT.
>
> Signed-off-by: Yan-Jie Wang <yanjiewtw@...il.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 9e5bab29685f..cc5abb3d54b9 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2552,10 +2552,10 @@
> 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.
Eh, I don't see any reason to have this one say "allow" instead of "enable/disable".
> - Default is 1 (enabled)
> + Default is 1 (allow)
>
> - kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
> - for all guests.
> + kvm-amd.npt= [KVM,AMD] Enable nested paging (virtualized MMU)
> + for all guests on capable AMD chips.
> Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
>
> kvm-arm.mode=
> @@ -2602,12 +2602,12 @@
> Format: <integer>
> Default: 5
>
> - kvm-intel.ept= [KVM,Intel] Disable extended page tables
> + kvm-intel.ept= [KVM,Intel] Enable extended page tables
> (virtualized MMU) support on capable Intel chips.
> Default is 1 (enabled)
>
> kvm-intel.emulate_invalid_guest_state=
> - [KVM,Intel] Disable emulation of invalid guest state.
> + [KVM,Intel] Enable 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
> @@ -2615,7 +2615,7 @@
> Default is 1 (enabled)
>
> kvm-intel.flexpriority=
> - [KVM,Intel] Disable FlexPriority feature (TPR shadow).
> + [KVM,Intel] Enable FlexPriority feature (TPR shadow).
> Default is 1 (enabled)
>
> kvm-intel.nested=
> @@ -2623,7 +2623,7 @@
> Default is 0 (disabled)
Heh, kvm-intel.nested has been enabled by default for quite some time. Can you
fix that up too?
>
> kvm-intel.unrestricted_guest=
> - [KVM,Intel] Disable unrestricted guest feature
> + [KVM,Intel] Enable unrestricted guest feature
> (virtualized real and unpaged mode) on capable
> Intel chips. Default is 1 (enabled)
>
> @@ -2639,7 +2639,7 @@
>
> Default is cond (do L1 cache flush in specific instances)
>
> - kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
> + kvm-intel.vpid= [KVM,Intel] Enable Virtual Processor Identification
> feature (tagged TLBs) on capable Intel chips.
> Default is 1 (enabled)
>
>
> base-commit: 865fdb08197e657c59e74a35fa32362b12397f58
> --
> 2.34.1
>
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