Re: [Xen-devel] [PATCH v2] xen/swiotlb: don't initialize swiotlb twice on arm64

From: Juergen Gross <jgross@suse.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: xen-devel@lists.xenproject.org, Julien.Grall@arm.com,
	Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [Xen-devel] [PATCH v2] xen/swiotlb: don't initialize swiotlb twice on arm64
Date: Wed, 5 Jun 2019 16:24:06 +0200	[thread overview]
Message-ID: <9d5a5e02-842f-fd2e-1b85-dd8a68600704@suse.com> (raw)
In-Reply-To: <20190605141354.GA16635@char.us.oracle.com>

On 05.06.19 16:13, Konrad Rzeszutek Wilk wrote:
> On Tue, Jun 04, 2019 at 03:41:40PM -0400, Boris Ostrovsky wrote:
>> 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>
> 
> Pushed in devel/for-linus-5.2 and will eventually move it to stable and push to Linus next-week.
> 
> Are there any other patches I should pick up?
> 

I think at least the first two patches from my series:

https://patchew.org/Xen/20190529090407.1225-1-jgross@suse.com/

are ready to go in.

Juergen

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