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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

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?

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