linux-kernel - Re: [PATCH 4.19 042/190] KVM: x86: hyperv: keep track of mismatched VP indexes

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Date:   Sun, 15 Sep 2019 18:55:16 +0200
From:   Pavel Machek <pavel@....cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 042/190] KVM: x86: hyperv: keep track of mismatched
 VP indexes

On Fri 2019-09-13 14:04:57, Greg Kroah-Hartman wrote:
> [ Upstream commit 87ee613d076351950b74383215437f841ebbeb75 ]
> 
> In most common cases VP index of a vcpu matches its vcpu index. Userspace is, however, 
> free to set any mapping it wishes and we need to account for that when we need to find a 
> vCPU with a particular VP index. To keep search algorithms optimal in both cases 
> introduce 'num_mismatched_vp_indexes' counter showing how many vCPUs with mismatching VP 
> index we have. In case the counter is zero we can assume vp_index == vcpu_idx.

I don't see why this is stable material.

>  	u64 hv_reenlightenment_control;
>  	u64 hv_tsc_emulation_control;
>  	u64 hv_tsc_emulation_status;
> +
> +	/* How many vCPUs have VP index != vCPU index */
> +	atomic_t num_mismatched_vp_indexes;
>  };
>  

It adds a write-only variable ...

Best regards,
									Pavel

-- 
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