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From: Christoph Helwig <hch@lst.de>
To: Joe Jin <joe.jin@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	"DONGLI.ZHANG" <dongli.zhang@oracle.com>,
	konrad@kernel.org, Christoph Helwig <hch@lst.de>,
	John Sobecki <john.sobecki@oracle.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] xen-swiotlb: exchange memory with Xen only when pages are contiguous
Date: Fri, 26 Oct 2018 09:48:02 +0200	[thread overview]
Message-ID: <20181026074802.GA4768@lst.de> (raw)
In-Reply-To: <5b64850f-9142-0360-fe4e-9e7bc74d2368@oracle.com>

On Thu, Oct 25, 2018 at 11:56:02AM -0700, Joe Jin wrote:
> I just discussed this patch with Boris in private, his opinions(Boris,
> please correct me if any misunderstood) are:
> 
> 1. With/without the check, both are incorrect, he thought we need to
>    prevented unalloc'd free at here. 
> 2. On freeing, if upper layer already checked the memory was DMA-able,
>    the checking at here does not make sense, we can remove all checks.
> 3. xen_create_contiguous_region() and xen_destroy_contiguous_region()
>    to come in pairs.
> 
> For #1 and #3, I think we need something associate it, like a list, on
> allocating, add addr to it, on freeing, check if in the list.

Is there any way to figure out based on an address if the exchange
operation happened?

> For #2, I'm was not found anywhere validated the address on 
> dma_free_coherent() callpath, not just xen-swiotlb.

At least for simple direct mappings there is no easy way to verify that
without keeping a list, and for some of the ops that do vmap like
operations we have basic santiy checks, but nothing that really catches
a wrong free.

  reply	other threads:[~2018-10-26  7:48 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-24  3:09 Joe Jin
2018-10-24 13:02 ` Konrad Rzeszutek Wilk
2018-10-24 13:57   ` Boris Ostrovsky
2018-10-24 14:43     ` Joe Jin
2018-10-25 11:45       ` Boris Ostrovsky
2018-10-25 14:23         ` Joe Jin
2018-10-25 16:10           ` Boris Ostrovsky
2018-10-25 16:28             ` Joe Jin
2018-10-25 18:56               ` Joe Jin
2018-10-26  7:48                 ` Christoph Helwig [this message]
2018-10-26  8:54                   ` Dongli Zhang
2018-10-26 14:48                     ` Joe Jin
2018-10-26 14:40                   ` Joe Jin
2018-10-30  2:51                 ` Joe Jin
     [not found]                   ` <57e5593233c64dc0a36c7d4c750a1ed4@AMSPEX02CL03.citrite.net>
2018-10-30 14:12                     ` [Xen-devel] " Joe Jin
     [not found]                       ` <097f1f6f16f7415aa3a52a7c4f5e52dc@AMSPEX02CL03.citrite.net>
2018-10-30 14:48                         ` Joe Jin
2018-10-24 16:05   ` Joe Jin

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