From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0ED5ECA9EA1 for ; Fri, 18 Oct 2019 06:42:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E33FA20820 for ; Fri, 18 Oct 2019 06:42:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2504432AbfJRGmf (ORCPT ); Fri, 18 Oct 2019 02:42:35 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:42106 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730508AbfJRGmf (ORCPT ); Fri, 18 Oct 2019 02:42:35 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=luoben@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0TfNs02I_1571380952; Received: from bn0418deMacBook-Pro.local(mailfrom:luoben@linux.alibaba.com fp:SMTPD_---0TfNs02I_1571380952) by smtp.aliyun-inc.com(127.0.0.1); Fri, 18 Oct 2019 14:42:33 +0800 Subject: Re: [PATCH] vfio/type1: remove hugepage checks in is_invalid_reserved_pfn() To: alex.williamson@redhat.com Cc: aarcange@redhat.com, linux-kernel@vger.kernel.org References: <1d6b7e1c40783f2db4c6cb15bf679a94222ec6a3.1570073993.git.luoben@linux.alibaba.com> <20191003164133.GG13922@redhat.com> From: Ben Luo Message-ID: Date: Fri, 18 Oct 2019 14:42:32 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191003164133.GG13922@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A friendly reminder :) Thanks,     Ben 在 2019/10/4 上午12:41, Andrea Arcangeli 写道: > On Thu, Oct 03, 2019 at 11:49:42AM +0800, Ben Luo wrote: >> Currently, no hugepage split code can transfer the reserved bit >> from head to tail during the split, so checking the head can't make >> a difference in a racing condition with hugepage spliting. >> >> The buddy wouldn't allow a driver to allocate an hugepage if any >> subpage is reserved in the e820 map at boot, if any driver sets the >> reserved bit of head page before mapping the hugepage in userland, >> it needs to set the reserved bit in all subpages to be safe. >> >> Signed-off-by: Ben Luo > Reviewed-by: Andrea Arcangeli > > >> --- >> drivers/vfio/vfio_iommu_type1.c | 26 ++++---------------------- >> 1 file changed, 4 insertions(+), 22 deletions(-) >> >> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c >> index 054391f..e2019ba 100644 >> --- a/drivers/vfio/vfio_iommu_type1.c >> +++ b/drivers/vfio/vfio_iommu_type1.c >> @@ -287,31 +287,13 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async) >> * Some mappings aren't backed by a struct page, for example an mmap'd >> * MMIO range for our own or another device. These use a different >> * pfn conversion and shouldn't be tracked as locked pages. >> + * For compound pages, any driver that sets the reserved bit in head >> + * page needs to set the reserved bit in all subpages to be safe. >> */ >> static bool is_invalid_reserved_pfn(unsigned long pfn) >> { >> - if (pfn_valid(pfn)) { >> - bool reserved; >> - struct page *tail = pfn_to_page(pfn); >> - struct page *head = compound_head(tail); >> - reserved = !!(PageReserved(head)); >> - if (head != tail) { >> - /* >> - * "head" is not a dangling pointer >> - * (compound_head takes care of that) >> - * but the hugepage may have been split >> - * from under us (and we may not hold a >> - * reference count on the head page so it can >> - * be reused before we run PageReferenced), so >> - * we've to check PageTail before returning >> - * what we just read. >> - */ >> - smp_rmb(); >> - if (PageTail(tail)) >> - return reserved; >> - } >> - return PageReserved(tail); >> - } >> + if (pfn_valid(pfn)) >> + return PageReserved(pfn_to_page(pfn)); >> >> return true; >> } >> -- >> 1.8.3.1 >>