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Tsirkin" To: Xie Yongji Cc: jasowang@redhat.com, xiaodong.liu@intel.com, maxime.coquelin@redhat.com, stefanha@redhat.com, songmuchun@bytedance.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/5] vduse: Remove unnecessary spin lock protection Message-ID: <20220713015352-mutt-send-email-mst@kernel.org> References: <20220706050503.171-1-xieyongji@bytedance.com> <20220706050503.171-2-xieyongji@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220706050503.171-2-xieyongji@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 vduse_domain_free_bounce_pages is not the only one taking this lock. 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. > --- > drivers/vdpa/vdpa_user/iova_domain.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c > index 6daa3978d290..bca1f0b8850c 100644 > --- a/drivers/vdpa/vdpa_user/iova_domain.c > +++ b/drivers/vdpa/vdpa_user/iova_domain.c > @@ -211,17 +211,14 @@ static struct page * > vduse_domain_get_bounce_page(struct vduse_iova_domain *domain, u64 iova) > { > struct vduse_bounce_map *map; > - struct page *page = NULL; > + struct page *page; > > - spin_lock(&domain->iotlb_lock); > map = &domain->bounce_maps[iova >> PAGE_SHIFT]; > if (!map->bounce_page) > - goto out; > + return NULL; > > page = map->bounce_page; > get_page(page); > -out: > - spin_unlock(&domain->iotlb_lock); > > return page; > } > -- > 2.20.1