[PATCH 1/2] Documentation: KVM: Update documentation to indicate KVM is arm64-only

[Marc Zyngier]

Hi Oliver,

Thanks for taking the hint! :D A few remarks below.

On Wed, 02 Mar 2022 19:42:20 +0000,
Oliver Upton <oupton at google.com> wrote:
> 
> KVM support for 32-bit ARM hosts (KVM/arm) has been removed from the
> kernel since commit 541ad0150ca4 ("arm: Remove 32bit KVM host
> support"). There still exists some remnants of the old architecture in
> the KVM documentation.
> 
> Remove all traces of 32-bit host support from the documentation. Note
> that AArch32 guests are still supported.
> 
> Fixes: 541ad0150ca4 ("arm: Remove 32bit KVM host support")

TBH, I'd drop the Fixes. Otherwise, it is going to be dragged into
-stable versions, and generate a number of pointless conflicts.

> Suggested-by: Marc Zyngier <maz at kernel.org>
> Signed-off-by: Oliver Upton <oupton at google.com>
> ---
>  Documentation/virt/kvm/api.rst          | 83 ++++++++++++-------------
>  Documentation/virt/kvm/arm/hyp-abi.rst  | 54 ++++++++--------
>  Documentation/virt/kvm/arm/ptp_kvm.rst  |  4 +-
>  Documentation/virt/kvm/devices/vcpu.rst |  2 +-
>  4 files changed, 70 insertions(+), 73 deletions(-)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 9f3172376ec3..25423ee890e2 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst

This part looks good.

> diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> index 4d43fbc25195..516ea630d160 100644
> --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> +++ b/Documentation/virt/kvm/arm/hyp-abi.rst

The content of this file is, however, still valid. Despite KVM having
been removed, the 32bit kernel still supports being entered at HYP
(bootloaders such as u-boot will definitely do that), and still uses
this internal API to switch back to HYP on kexec. Other hypervisors
(such as jailhouse) also rely on this API to install themselves at
runtime.

> diff --git a/Documentation/virt/kvm/arm/ptp_kvm.rst b/Documentation/virt/kvm/arm/ptp_kvm.rst
> index aecdc80ddcd8..5d47f7ecbf5a 100644
> --- a/Documentation/virt/kvm/arm/ptp_kvm.rst
> +++ b/Documentation/virt/kvm/arm/ptp_kvm.rst
> @@ -1,7 +1,7 @@
>  .. SPDX-License-Identifier: GPL-2.0
>  
> -PTP_KVM support for arm/arm64
> -=============================
> +PTP_KVM support for arm64

This is a service that the arm64 hypervisor offers to guests,
including 32bit guests. It was actually merged after 32bit port was
removed. So this file should probably stay untouched, or be amended to
clarify the nuance in terms of support.

> +=========================
>  
>  PTP_KVM is used for high precision time sync between host and guests.
>  It relies on transferring the wall clock and counter value from the
> diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
> index 60a29972d3f1..92942440a9e7 100644
> --- a/Documentation/virt/kvm/devices/vcpu.rst
> +++ b/Documentation/virt/kvm/devices/vcpu.rst

This one is OK.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.