linux-kernel - Re: [PATCH v2 1/5] vduse: Remove unnecessary spin lock protection

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Message-ID: <CACycT3uu3DWsLTH8b4GhTLS74hmduH5ugaKGEqaoBrdQckyPow@mail.gmail.com>
Date:   Wed, 13 Jul 2022 18:39:04 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Liu Xiaodong <xiaodong.liu@...el.com>,
        Maxime Coquelin <maxime.coquelin@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        songmuchun@...edance.com,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] vduse: Remove unnecessary spin lock protection

On Wed, Jul 13, 2022 at 1:57 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Wed, Jul 06, 2022 at 01:04:59PM +0800, Xie Yongji wrote:
> > Taking iotlb lock to access bounce page in page fault
> > handler is meaningless since vduse_domain_free_bounce_pages()
> > would only be called during file release.
> >
> > Signed-off-by: Xie Yongji <xieyongji@...edance.com>
>
> vduse_domain_free_bounce_pages is not the
> only one taking this lock.

Yes, but only vduse_domain_free_bounce_pages() is to protect
domain->bounce_maps with this lock. In other places, the lock is used
to protect the domain->iotlb.

> This commit log needs more
> analysis documenting all points of access to bounce_maps
> and why vduse_domain_get_bounce_page and file
> release are the only two.
>

OK, I will explain that we actually protect two different variables
(domain->bounce_maps and domain->iotlb) with one lock.

Thanks,
Yongji