linux-kernel - Re: [PATCH v2] Documentation: KVM: Add reference specs for PIT and LAPIC ioctls

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Message-ID: <bccc8f53-9efa-4844-af5d-9abfe4446d06@infradead.org>
Date: Fri, 5 Sep 2025 12:17:28 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Jiaming Zhang <r772577952@...il.com>
Cc: corbet@....net, kvm@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, pbonzini@...hat.com, seanjc@...gle.com
Subject: Re: [PATCH v2] Documentation: KVM: Add reference specs for PIT and
 LAPIC ioctls



On 9/5/25 10:47 AM, Jiaming Zhang wrote:
> ---
> 
> The behavior of KVM_SET_PIT2 and KVM_SET_LAPIC conforms to their
> respective hardware specifications. Add references to the Intel 8254
> PIT datasheet and the Software Developer's Manual (SDM)  to ensure
> users can rely on the official datasheets for behavioral details.
> 
> Signed-off-by: Jiaming Zhang <r772577952@...il.com>

Thanks. LGTM.

Reviewed-by: Randy Dunlap <rdunlap@...radead.org>

> ---
>  Documentation/virt/kvm/api.rst | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 6aa40ee05a4a..f55e1b7562db 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -2083,6 +2083,11 @@ The format of the APIC ID register (bytes 32-35 of struct kvm_lapic_state's
>  regs field) depends on the state of the KVM_CAP_X2APIC_API capability.
>  See the note in KVM_GET_LAPIC.
>  
> +.. Tip::
> +  ``KVM_SET_LAPIC`` ioctl strictly adheres to Intel® 64 and IA-32 Architectures
> +  Software Developer's Manual (SDM). Refer to volume 3A of the `Intel SDM
> +  <https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html>`_.
> +
>  
>  4.59 KVM_IOEVENTFD
>  ------------------
> @@ -3075,6 +3080,13 @@ This IOCTL replaces the obsolete KVM_GET_PIT.
>  Sets the state of the in-kernel PIT model. Only valid after KVM_CREATE_PIT2.
>  See KVM_GET_PIT2 for details on struct kvm_pit_state2.
>  
> +.. Tip::
> +
> +  ``KVM_SET_PIT2`` ioctl strictly adheres to the spec of Intel 8254 PIT.
> +  For example, a ``count`` value of 0 in ``struct kvm_pit_channel_state`` is
> +  interpreted as 65536, which is the maximum count value. Refer to `Intel 8254
> +  programmable interval timer <https://www.scs.stanford.edu/10wi-cs140/pintos/specs/8254.pdf>`_.
> +
>  This IOCTL replaces the obsolete KVM_SET_PIT.
>  
>  

-- 
~Randy