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Thu, 25 Oct 2018 11:46:02 +0000 Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserv0021.oracle.com (8.14.4/8.14.4) with ESMTP id w9PBk2N6002403 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 25 Oct 2018 11:46:02 GMT Received: from abhmp0020.oracle.com (abhmp0020.oracle.com [141.146.116.26]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w9PBk1Vm004899; Thu, 25 Oct 2018 11:46:02 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 25 Oct 2018 04:45:57 -0700 Subject: Re: [PATCH] xen-swiotlb: exchange memory with Xen only when pages are contiguous To: Joe Jin , Konrad Rzeszutek Wilk Cc: "DONGLI.ZHANG" , konrad@kernel.org, Christoph Helwig , John Sobecki , "xen-devel@lists.xenproject.org" , "linux-kernel@vger.kernel.org\"" References: <20181024130246.GA22616@localhost.localdomain> <83900cf4-690c-9725-d022-d427fdeb4f7d@oracle.com> <581cb7ea-3112-791d-918d-9bb887e4744f@oracle.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <581cb7ea-3112-791d-918d-9bb887e4744f@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9056 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1810250105 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/24/18 10:43 AM, Joe Jin wrote: > On 10/24/18 6:57 AM, Boris Ostrovsky wrote: >> On 10/24/18 9:02 AM, Konrad Rzeszutek Wilk wrote: >>> On Tue, Oct 23, 2018 at 08:09:04PM -0700, Joe Jin wrote: >>>> Commit 4855c92dbb7 "xen-swiotlb: fix the check condition for >>>> xen_swiotlb_free_coherent" only fixed memory address check condition >>>> on xen_swiotlb_free_coherent(), when memory was not physically >>>> contiguous and tried to exchanged with Xen via >>>> xen_destroy_contiguous_region it will lead kernel panic. >>> s/it will lead/which lead to/? >>> >>>> The correct check condition should be memory is in DMA area and >>>> physically contiguous. >>> "The correct check condition to make Xen hypercall to revert the >>> memory back from its 32-bit pool is if it is: >>> 1) Above its DMA bit mask (for example 32-bit devices can only address >>> up to 4GB, and we may want 4GB+2K), and >> Is this "and' or 'or'? >> >>> 2) If it not physically contingous >>> >>> N.B. The logic in the code is inverted, which leads to all sorts of >>> confusions." >> >> I would, in fact, suggest to make the logic the same in both >> xen_swiotlb_alloc_coherent() and xen_swiotlb_free_coherent() to avoid >> this. This will involve swapping if and else in the former. >> >> >>> Does that sound correct? >>> >>>> Thank you Boris for pointing it out. >>>> >>> Fixes: 4855c92dbb7 ("xen-sw..") ? >>> >>>> Signed-off-by: Joe Jin >>>> Cc: Konrad Rzeszutek Wilk >>>> Cc: Boris Ostrovsky >>> Reported-by: Boris Ostrovs... ? >>>> Cc: Christoph Helwig >>>> Cc: Dongli Zhang >>>> Cc: John Sobecki >>>> --- >>>> drivers/xen/swiotlb-xen.c | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c >>>> index f5c1af4ce9ab..aed92fa019f9 100644 >>>> --- a/drivers/xen/swiotlb-xen.c >>>> +++ b/drivers/xen/swiotlb-xen.c >>>> @@ -357,8 +357,8 @@ 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) && >>>> + !range_straddles_page_boundary(phys, size)) >>>> xen_destroy_contiguous_region(phys, order); >> >> I don't think this is right. >> >> if ((dev_addr + size - 1 > dma_mask) || range_straddles_page_boundary(phys, size)) >> >> No? > No this is not correct. > > When allocate memory, it tried to allocated from Dom0/Guest, then check if physical > address is DMA memory also contiguous, if no, exchange with Hypervisor, code as below: > > 326 phys = *dma_handle; > 327 dev_addr = xen_phys_to_bus(phys); > 328 if (((dev_addr + size - 1 <= dma_mask)) && > 329 !range_straddles_page_boundary(phys, size)) > 330 *dma_handle = dev_addr; > 331 else { > 332 if (xen_create_contiguous_region(phys, order, > 333 fls64(dma_mask), dma_handle) != 0) { > 334 xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs); > 335 return NULL; > 336 } > 337 } > > > On freeing, need to return the memory to Xen, otherwise DMA memory will be used > up(this is the issue the patch intend to fix), so when memory is DMAable and > contiguous then call xen_destroy_contiguous_region(), return DMA memory to Xen. So if you want to allocate 1 byte at address 0 (and dev_addr=phys), xen_create_contiguous_region() will not be called. And yet you will call xen_destroy_contiguous_region() in the free path. Is this the expected behavior? -boris