From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: jgross@suse.com, xen-devel@lists.xenproject.org,
Julien.Grall@arm.com, konrad.wilk@oracle.com
Subject: Re: [Xen-devel] [PATCH v2] xen/swiotlb: don't initialize swiotlb twice on arm64
Date: Tue, 4 Jun 2019 15:41:40 -0400 [thread overview]
Message-ID: <4e4bef15-3e0a-c4a3-7b82-ddadb687e684@oracle.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1906040949090.14041@sstabellini-ThinkPad-T480s>
On 6/4/19 12:51 PM, Stefano Stabellini wrote:
> On Mon, 3 Jun 2019, Boris Ostrovsky wrote:
>> On 6/3/19 2:25 PM, Stefano Stabellini wrote:
>>> On Tue, 28 May 2019, Boris Ostrovsky wrote:
>>>> On 5/28/19 6:48 PM, Stefano Stabellini wrote:
>>>>> From: Stefano Stabellini <stefanos@xilinx.com>
>>>>>
>>>>> On arm64 swiotlb is often (not always) already initialized by mem_init.
>>>>> We don't want to initialize it twice, which would trigger a second
>>>>> memory allocation. Moreover, the second memory pool is typically made of
>>>>> high pages and ends up replacing the original memory pool of low pages.
>>>>> As a side effect of this change, it is possible to have low pages in
>>>>> swiotlb-xen on arm64.
>>>>>
>>>>> Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
>>>> Has this been tested on x86?
>>> Yes, I managed to test it using QEMU. There are no effects on x86, as
>>> the check io_tlb_start != 0 returns false.
>> I wonder though whether this is always the case. When we are called
>> from pci_xen_swiotlb_init_late() for example.
> In that case, pci_xen_swiotlb_init_late() is called by
> pcifront_connect_and_init_dma, which does:
>
> if (!err && !swiotlb_nr_tbl()) {
> err = pci_xen_swiotlb_init_late();
> if (err)
> dev_err(&pdev->xdev->dev, "Could not setup SWIOTLB!\n");
> }
>
> pci_xen_swiotlb_init_late() is only called when swiotlb_nr_tbl() returns
> 0. If swiotlb_nr_tbl() returns 0, certainly the swiotlb has not been
> allocated yet, and the io_tlb_start != 0 check at the beginning of
> xen_swiotlb_init will also fail. The code will take the normal
> route, same as today. In short, there should be no effects on x86.
OK, thanks.
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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next prev parent reply other threads:[~2019-06-04 19:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-28 22:48 [PATCH v2] xen/swiotlb: don't initialize swiotlb twice on arm64 Stefano Stabellini
2019-05-28 22:48 ` [Xen-devel] " Stefano Stabellini
2019-05-28 23:50 ` Boris Ostrovsky
2019-05-28 23:50 ` [Xen-devel] " Boris Ostrovsky
2019-06-03 18:25 ` Stefano Stabellini
2019-06-03 18:25 ` [Xen-devel] " Stefano Stabellini
2019-06-03 23:16 ` Boris Ostrovsky
2019-06-03 23:16 ` [Xen-devel] " Boris Ostrovsky
2019-06-04 16:51 ` Stefano Stabellini
2019-06-04 19:41 ` Boris Ostrovsky [this message]
2019-06-05 14:13 ` Konrad Rzeszutek Wilk
2019-06-05 14:24 ` Juergen Gross
2019-06-13 14:23 ` Konrad Rzeszutek Wilk
2019-06-13 15:04 ` Juergen Gross
2019-06-13 21:00 ` Konrad Rzeszutek Wilk
2019-06-17 8:21 ` Christoph Hellwig
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