> -----Original Message----- > From: Xen-devel [mailto:xen-devel-boun...@lists.xenproject.org] On Behalf > Of Joe Jin > Sent: 30 October 2018 14:13 > To: Paul Durrant <paul.durr...@citrix.com>; Boris Ostrovsky > <boris.ostrov...@oracle.com>; Konrad Rzeszutek Wilk > <konrad.w...@oracle.com> > Cc: John Sobecki <john.sobe...@oracle.com>; DONGLI.ZHANG > <dongli.zh...@oracle.com>; linux-ker...@vger.kernel.org" <linux- > ker...@vger.kernel.org>; kon...@kernel.org; xen- > de...@lists.xenproject.org; Christoph Helwig <h...@lst.de> > Subject: Re: [Xen-devel] [PATCH] xen-swiotlb: exchange memory with Xen > only when pages are contiguous > > On 10/30/18 1:59 AM, Paul Durrant wrote: > >> On 10/25/18 11:56 AM, Joe Jin wrote: > >>> I just discussed this patch with Boris in private, his opinions(Boris, > >>> please correct me if any misunderstood) are: > >>> > >>> 1. With/without the check, both are incorrect, he thought we need to > >>> prevented unalloc'd free at here. > >>> 2. On freeing, if upper layer already checked the memory was DMA-able, > >>> the checking at here does not make sense, we can remove all checks. > >>> 3. xen_create_contiguous_region() and xen_destroy_contiguous_region() > >>> to come in pairs. > >> I tried to added radix_tree to track allocating/freeing and I found > some > >> memory only allocated but was not freed, I guess it caused by driver > used > >> dma_pool, that means if lots of such requests, the list will consume > lot > >> of memory for it. Will continue to work on it, if anyone have good idea > >> for it please let me know, I'd like to try it. > >> > > FWIW, in my Xen PV-IOMMU test patches, I have also tried keeping a list > of ranges mapped for DMA and have discovered apparent issues with some > drivers, particularly tg3, that seem to free mappings that have not been > allocated (or possibly double-free). I've never fully tracked down the > issue. > > Call trace of first called xen_swiotlb_alloc_coherent(The pages never > backed to Xen): > > [ 23.436333] [<ffffffff814040c9>] > xen_swiotlb_alloc_coherent+0x169/0x510 > [ 23.436623] [<ffffffff811eb38d>] ? kmem_cache_alloc_trace+0x1ed/0x280 > [ 23.436900] [<ffffffff811d72af>] dma_pool_alloc+0x11f/0x260 > [ 23.437190] [<ffffffff81537442>] ehci_qh_alloc+0x52/0x120 > [ 23.437481] [<ffffffff8153b80f>] ehci_setup+0x2bf/0x8e0 > [ 23.437760] [<ffffffff81476d06>] ? __dev_printk+0x46/0xa0 > [ 23.438042] [<ffffffff814770b3>] ? _dev_info+0x53/0x60 > [ 23.438327] [<ffffffff8153f620>] ehci_pci_setup+0xc0/0x5f0 > [ 23.438615] [<ffffffff81519fcd>] usb_add_hcd+0x25d/0xaf0 > [ 23.438901] [<ffffffff8152c9a6>] usb_hcd_pci_probe+0x406/0x520 > [ 23.439177] [<ffffffff8153f486>] ehci_pci_probe+0x36/0x40 > [ 23.439469] [<ffffffff8136e99a>] local_pci_probe+0x4a/0xb0 > [ 23.439752] [<ffffffff8136fba5>] ? pci_match_device+0xe5/0x110 > [ 23.440027] [<ffffffff8136fce1>] pci_device_probe+0xd1/0x120 > [ 23.440320] [<ffffffff8147b13c>] driver_probe_device+0x20c/0x4d0 > [ 23.440599] [<ffffffff8147b4eb>] __driver_attach+0x9b/0xa0 > [ 23.440879] [<ffffffff8147b450>] ? __device_attach+0x50/0x50 > > Above was EHCI used DMA pool to allocate DMA memory. > > During my testing, ~1000 entries was not freed, if more PCI devices > use DMA pool, the tree/list will have more entries, looks it's not a > good idea that use a list to track it. >
Yes, it seems pools can hang onto a serious number of allocations so a list is probably not wise. What I was pointing out, though, is that it appears you can't even track mappings (as opposed to allocations) with a list either because drivers apparently try to unmap things they have not mapped. Paul > Thanks, > Joe > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xenproject.org > https://lists.xenproject.org/mailman/listinfo/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel