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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Xie Yongji <xieyongji@bytedance.com>
Cc: xiaodong.liu@intel.com, linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	maxime.coquelin@redhat.com, stefanha@redhat.com,
	songmuchun@bytedance.com
Subject: Re: [PATCH v2 1/5] vduse: Remove unnecessary spin lock protection
Date: Wed, 13 Jul 2022 01:57:23 -0400	[thread overview]
Message-ID: <20220713015352-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20220706050503.171-2-xieyongji@bytedance.com>

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@bytedance.com>

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

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WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Xie Yongji <xieyongji@bytedance.com>
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
Date: Wed, 13 Jul 2022 01:57:23 -0400	[thread overview]
Message-ID: <20220713015352-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20220706050503.171-2-xieyongji@bytedance.com>

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@bytedance.com>

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


  parent reply	other threads:[~2022-07-13  5:57 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-07-06  5:04 [PATCH v2 0/5] VDUSE: Support registering userspace memory as bounce buffer Xie Yongji
2022-07-06  5:04 ` [PATCH v2 1/5] vduse: Remove unnecessary spin lock protection Xie Yongji
2022-07-13  5:43   ` Jason Wang
2022-07-13  5:43     ` Jason Wang
2022-07-13 11:08     ` Yongji Xie
2022-07-14  2:27       ` Jason Wang
2022-07-14  2:27         ` Jason Wang
2022-07-14  6:06         ` Yongji Xie
2022-07-13  5:57   ` Michael S. Tsirkin [this message]
2022-07-13  5:57     ` Michael S. Tsirkin
2022-07-13 10:39     ` Yongji Xie
2022-07-06  5:05 ` [PATCH v2 2/5] vduse: Use memcpy_{to,from}_page() in do_bounce() Xie Yongji
2022-07-13  5:59   ` Jason Wang
2022-07-13  5:59     ` Jason Wang
2022-07-06  5:05 ` [PATCH v2 3/5] vduse: Support using userspace pages as bounce buffer Xie Yongji
2022-07-06  5:05 ` [PATCH v2 4/5] vduse: Support querying IOLTB information Xie Yongji
2022-07-14  2:51   ` Jason Wang
2022-07-14  2:51     ` Jason Wang
2022-07-14  5:58     ` Yongji Xie
2022-07-06  5:05 ` [PATCH v2 5/5] vduse: Support registering userspace memory for IOTLB Xie Yongji
2022-07-06  6:08   ` kernel test robot
2022-07-06  6:08     ` kernel test robot
2022-07-07 23:01   ` kernel test robot
2022-07-07 23:01     ` kernel test robot
2022-07-08  1:14   ` kernel test robot
2022-07-08  1:14     ` kernel test robot
2022-07-06  9:30 ` [PATCH v2 0/5] VDUSE: Support registering userspace memory as bounce buffer Jason Wang
2022-07-06  9:30   ` Jason Wang
2022-07-06 10:15   ` Yongji Xie
2022-07-08  8:38     ` Jason Wang
2022-07-08  8:38       ` Jason Wang
2022-07-08  9:53       ` Yongji Xie
2022-07-11  6:02         ` Jason Wang
2022-07-11  6:02           ` Jason Wang
2022-07-11  7:24           ` Yongji Xie
2022-07-14  2:59             ` Jason Wang
2022-07-14  2:59               ` Jason Wang

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