On Thu, 2018-06-07 at 13:59 -0700, Joe Jin wrote: > On 6/7/18 1:28 PM, Ben Hutchings wrote: > > On Mon, 2018-05-28 at 11:59 +0200, Greg Kroah-Hartman wrote: > > > 4.4-stable review patch. If anyone has any objections, please let me know. > > > > > > ------------------ > > > > > > From: Joe Jin <joe.jin@xxxxxxxxxx> > > > > > > commit 4855c92dbb7b3b85c23e88ab7ca04f99b9677b41 upstream. > > > > > > When run raidconfig from Dom0 we found that the Xen DMA heap is reduced, > > > but Dom Heap is increased by the same size. Tracing raidconfig we found > > > that the related ioctl() in megaraid_sas will call dma_alloc_coherent() > > > to apply memory. If the memory allocated by Dom0 is not in the DMA area, > > > it will exchange memory with Xen to meet the requiment. Later drivers > > > call dma_free_coherent() to free the memory, on xen_swiotlb_free_coherent() > > > the check condition (dev_addr + size - 1 <= dma_mask) is always false, > > > > I think this was meant to say (dev_addr + size - 1 > dma_mask), i.e. > > Hi Ben, > > Yes you are right, sorry I made the mistake, thanks for catch it. > Is there any way to fix description from git repo? No there isn't, but that wasn't my main point. Please address the rest of my message. Ben. > Regards, > Joe > > > the condition that is replaced by this commit. If that's always false, > > the new condition (the logical inverse) must always be true. > > > > [...] > > > --- a/drivers/xen/swiotlb-xen.c > > > +++ b/drivers/xen/swiotlb-xen.c > > > @@ -359,7 +359,7 @@ xen_swiotlb_free_coherent(struct device > > > * physical address */ > > > phys = xen_bus_to_phys(dev_addr); > > > > > > - if (((dev_addr + size - 1 > dma_mask)) || > > > + if (((dev_addr + size - 1 <= dma_mask)) || > > > range_straddles_page_boundary(phys, size)) > > > xen_destroy_contiguous_region(phys, order); > > > > > > > So now we will always call xen_destroy_contiguous_region(), whether or > > not xen_create_contiguous_region() was called during allocation. Is > > that really the intent? If so, the entire condition could be removed > > to make this clear. > > > > Alternately, if the commit message is correct, the condition could be > > simplified to range_straddles_page_boundary(...). > > > > But I'm not at all convinced that either of these is correct. It seems > > like you need to either find a way of distinguishing between memory > > allocated with or without the use of xen_create_contiguous_region(), or > > to use it unconditionally. > > > > Ben. > > > > -- Ben Hutchings, Software Developer Codethink Ltd https://www.codethink.co.uk/ Dale House, 35 Dale Street Manchester, M1 2HF, United Kingdom
