[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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



On 13.06.19 16:23, Konrad Rzeszutek Wilk wrote:
On Wed, Jun 05, 2019 at 04:24:06PM +0200, Juergen Gross wrote:
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@xxxxxxxxxx>

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@xxxxxxxxxx>
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@xxxxxxxxxx>

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@xxxxxxxx/

are ready to go in.

#2 patch says:

        "> To be symmetric with setting the flag only after having made the 
region
        > contiguous, and to avoid (perhaps just theoretical) races, wouldn't 
it be
        > better to clear the flag before calling 
xen_destroy_contiguous_region()?
        > Even better would be a TestAndClear...() operation.

        I like that idea.
"
?

I was hoping for a clarification regarding the Xen specific page flag
names before posting V3.

As Christoph didn't react when I posted possible solutions I think I'll
just modify patch 3 according to Jan's comment and post V3.


Juergen

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.