linux-kernel - Re: [PATCH v2] doc: kvm: Fix return description of KVM_SET

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Date:   Wed, 4 Sep 2019 10:41:22 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Jonathan Corbet <corbet@....net>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] doc: kvm: Fix return description of KVM_SET_MSRS

On Wed, Sep 04, 2019 at 02:01:18PM +0800, Xiaoyao Li wrote:
> Userspace can use ioctl KVM_SET_MSRS to update a set of MSRs of guest.
> This ioctl sets specified MSRs one by one. Once it fails to set an MSR
> due to setting reserved bits, the MSR is not supported/emulated by kvm,
> or violating other restrictions, it stops further processing and returns
> the number of MSRs have been set successfully.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
> v2:
>   elaborate the changelog and description of ioctl KVM_SET_MSRS based on
>   Sean's comments.
> 
> ---
>  Documentation/virt/kvm/api.txt | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
> index 2d067767b617..4638e893dec0 100644
> --- a/Documentation/virt/kvm/api.txt
> +++ b/Documentation/virt/kvm/api.txt
> @@ -586,7 +586,7 @@ Capability: basic
>  Architectures: x86
>  Type: vcpu ioctl
>  Parameters: struct kvm_msrs (in)
> -Returns: 0 on success, -1 on error
> +Returns: number of msrs successfully set (see below), -1 on error
>  
>  Writes model-specific registers to the vcpu.  See KVM_GET_MSRS for the
>  data structures.
> @@ -595,6 +595,11 @@ Application code should set the 'nmsrs' member (which indicates the
>  size of the entries array), and the 'index' and 'data' members of each
>  array entry.
>  
> +It tries to set the MSRs in array entries[] one by one. Once failing to

Probably better to say 'If' as opposed to 'Once', don't want to imply that
userspace is incompetent :)

> +set an MSR (due to setting reserved bits, the MSR is not supported/emulated
> +by kvm, or violating other restrctions), 

Make it clear the list is not exhaustive, e.g.:

It tries to set the MSRs in array entries[] one by one.  If setting an MSR
fails, e.g. due to setting reserved bits, the MSR isn't supported/emulated by
KVM, etc..., it stops processing the MSR list and returns the number of MSRs
that have been set successfully.

> it stops setting following MSRs
> +and returns the number of MSRs have been set successfully.
> +
>  
>  4.20 KVM_SET_CPUID
>  
> -- 
> 2.19.1
>