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

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Date:   Thu, 5 Sep 2019 09:11:53 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...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 9/5/2019 1:41 AM, Sean Christopherson wrote:
> 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.
>

Refine it as you commented and send out v3, thanks.

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