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Re: [Xen-devel] [PATCH 1/3] xen/swiotlb: fix condition for calling xen_destroy_contiguous_region()
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Thu, 25 Apr 2019 10:55:33 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, lkml <linux-kernel@xxxxxxxxxxxxxxx>, stable@xxxxxxxxxxxxxxx, iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Delivery-date: Thu, 25 Apr 2019 08:55:40 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 25/04/2019 10:53, Jan Beulich wrote:
>>>> On 23.04.19 at 12:54, <jgross@xxxxxxxx> wrote:
>> --- a/drivers/xen/swiotlb-xen.c
>> +++ b/drivers/xen/swiotlb-xen.c
>> @@ -360,8 +360,8 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t
>> size, void *vaddr,
>> /* Convert the size to actually allocated. */
>> size = 1UL << (order + XEN_PAGE_SHIFT);
>>
>> - if (((dev_addr + size - 1 <= dma_mask)) ||
>> - range_straddles_page_boundary(phys, size))
>> + if ((dev_addr + size - 1 <= dma_mask) &&
>> + !WARN_ON(range_straddles_page_boundary(phys, size)))
>> xen_destroy_contiguous_region(phys, order);
>
> On the allocation side we have
>
> if (((dev_addr + size - 1 <= dma_mask)) &&
> !range_straddles_page_boundary(phys, size))
> *dma_handle = dev_addr;
> else {
> if (xen_create_contiguous_region(phys, order,
> fls64(dma_mask), dma_handle)
> != 0) {
> xen_free_coherent_pages(hwdev, size, ret,
> (dma_addr_t)phys, attrs);
> return NULL;
> }
> }
>
> which is (as far as the function call is concerned)
>
> if ((dev_addr + size - 1 > dma_mask) ||
> range_straddles_page_boundary(phys, size))
> xen_create_contiguous_region(...);
>
> So I don't think your transformation is correct. Even worse, both
> parts of the condition in xen_swiotlb_free_coherent() act on an
> address that is the _result_ of the prior
> xen_create_contiguous_region(), i.e. the address should always
> match _both_ criteria anyway. Whereas what you really want is
> undo the xen_create_contiguous_region() only when it actually
> was called. Otherwise you also shatter contiguous allocations
> that were contiguous already for other reasons (perhaps just
> luck).
Yes, that is what patch 3 does.
Juergen
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