linux-kernel - Re: [PATCH v7 09/18] virt: acrn: Introduce I/O request management

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Message-ID: <20210111215219.l44yfpyqh4m2mcbl@offworld>
Date:   Mon, 11 Jan 2021 13:52:19 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     shuo.a.liu@...el.com
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Yu Wang <yu1.wang@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>
Subject: Re: [PATCH v7 09/18] virt: acrn: Introduce I/O request management

On Wed, 06 Jan 2021, shuo.a.liu@...el.com wrote:
>The processing flow of I/O requests are listed as following:
>
>a) The I/O handler of the hypervisor will fill an I/O request with
>   PENDING state when a trapped I/O access happens in a User VM.
>b) The hypervisor makes an upcall, which is a notification interrupt, to
>   the Service VM.
>c) The upcall handler schedules a tasklet to dispatch I/O requests.
>d) The tasklet looks for the PENDING I/O requests, assigns them to
>   different registered clients based on the address of the I/O accesses,
>   updates their state to PROCESSING, and notifies the corresponding
>   client to handle.

Hmm so tasklets are deprecated (and have been for a while) and it's sad
to see incoming new users in modern Linux. This wouldn't be the first one,
however. We should be _removing_ users, not adding... In addition, this
expands the whole tasklet_disable/enable() hacks.

Could this not be done in process context instead?

Thanks,
Davidlohr