Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751292AbdFAPiv (ORCPT ); Thu, 1 Jun 2017 11:38:51 -0400 Received: from foss.arm.com ([217.140.101.70]:57548 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751078AbdFAPit (ORCPT ); Thu, 1 Jun 2017 11:38:49 -0400 Subject: Re: [PATCH] xen/privcmd: Support correctly 64KB page granularity when mapping memory To: Boris Ostrovsky , xen-devel@lists.xen.org References: <20170531130357.14492-1-julien.grall@arm.com> <7199e366-f56a-acc8-ffa5-0c85d6975049@oracle.com> <592886a8-1443-6475-e318-85cb9acecead@arm.com> <0b91491d-8f67-fa22-8b27-7692f00bba51@arm.com> Cc: sstabellini@kernel.org, jgross@suse.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Feng Kan From: Julien Grall Message-ID: <1f38dcc0-8538-b8e5-a792-85867ea1c44d@arm.com> Date: Thu, 1 Jun 2017 16:38:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2885 Lines: 83 Hi Boris, On 01/06/17 16:16, Boris Ostrovsky wrote: > On 06/01/2017 10:01 AM, Julien Grall wrote: >> Hi Boris, >> >> On 01/06/17 14:33, Boris Ostrovsky wrote: >>> On 06/01/2017 08:50 AM, Julien Grall wrote: >>>> Hi Boris, >>>> >>>> On 31/05/17 14:54, Boris Ostrovsky wrote: >>>>> On 05/31/2017 09:03 AM, Julien Grall wrote: >>>>>> Commit 5995a68 "xen/privcmd: Add support for Linux 64KB page >>>>>> granularity" did >>>>>> not go far enough to support 64KB in mmap_batch_fn. >>>>>> >>>>>> The variable 'nr' is the number of 4KB chunk to map. However, when >>>>>> Linux >>>>>> is using 64KB page granularity the array of pages >>>>>> (vma->vm_private_data) >>>>>> contain one page per 64KB. Fix it by incrementing st->index >>>>>> correctly. >>>>>> >>>>>> Furthermore, st->va is not correctly incremented as PAGE_SIZE != >>>>>> XEN_PAGE_SIZE. >>>>>> >>>>>> Fixes: 5995a68 ("xen/privcmd: Add support for Linux 64KB page >>>>>> granularity") >>>>>> CC: stable@vger.kernel.org >>>>>> Reported-by: Feng Kan >>>>>> Signed-off-by: Julien Grall >>>>>> --- >>>>>> drivers/xen/privcmd.c | 4 ++-- >>>>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c >>>>>> index 7a92a5e1d40c..feca75b07fdd 100644 >>>>>> --- a/drivers/xen/privcmd.c >>>>>> +++ b/drivers/xen/privcmd.c >>>>>> @@ -362,8 +362,8 @@ static int mmap_batch_fn(void *data, int nr, >>>>>> void *state) >>>>>> st->global_error = 1; >>>>>> } >>>>>> } >>>>>> - st->va += PAGE_SIZE * nr; >>>>>> - st->index += nr; >>>>>> + st->va += XEN_PAGE_SIZE * nr; >>>>>> + st->index += nr / XEN_PFN_PER_PAGE; >>>>>> >>>>>> return 0; >>>>>> } >>>>> >>>>> >>>>> Are we still using PAGE_MASK for xen_remap_domain_gfn_array()? >>>> >>>> Do you mean in the xen_xlate_remap_gfn_array implementation? If so >>>> there are no use of PAGE_MASK as the code has been converted to >>>> support 64K page granularity. >>>> >>>> If you mean the x86 version of xen_remap_domain_gfn_array, then we >>>> don't really care as x86 only use 4KB page granularity. >>> >>> >>> I meant right above the change that you made. Should it also be replaced >>> with XEN_PAGE_MASK? (Sorry for being unclear.) >> >> Oh. The code in xen_remap_domain_gfn_array is relying on st->va to be >> page aligned. So I think we want to keep PAGE_MASK here. > > Doe this imply then that 'nr' 4K pages is integral number of PAGE_SIZE > (i.e. (nr*XEN_PAGE_SIZE) % PAGE_SIZE == 0) and if yes --- do we test > this somewhere? I don't see it. nr might be smaller for the last batch. But all the intermediate batch should have ((nr * XEN_PAGE_SIZE) % PAGE_SIZE == 0). I think the BUILD_BUG_ON in privcmd_ioctl_mmap_batch ensure that all the intermediate batch will always be an integral number of PAGE_SIZE. Cheers, -- Julien Grall