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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 BF08DC10F14 for ; Thu, 3 Oct 2019 16:41:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A050A206BB for ; Thu, 3 Oct 2019 16:41:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405079AbfJCQlq (ORCPT ); Thu, 3 Oct 2019 12:41:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34588 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405064AbfJCQlj (ORCPT ); Thu, 3 Oct 2019 12:41:39 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 590FE18C4290; Thu, 3 Oct 2019 16:41:39 +0000 (UTC) Received: from mail (ovpn-120-134.rdu2.redhat.com [10.10.120.134]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0481C5C226; Thu, 3 Oct 2019 16:41:33 +0000 (UTC) Date: Thu, 3 Oct 2019 12:41:33 -0400 From: Andrea Arcangeli To: Ben Luo Cc: alex.williamson@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] vfio/type1: remove hugepage checks in is_invalid_reserved_pfn() Message-ID: <20191003164133.GG13922@redhat.com> References: <1d6b7e1c40783f2db4c6cb15bf679a94222ec6a3.1570073993.git.luoben@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1d6b7e1c40783f2db4c6cb15bf679a94222ec6a3.1570073993.git.luoben@linux.alibaba.com> User-Agent: Mutt/1.12.2 (2019-09-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.62]); Thu, 03 Oct 2019 16:41:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >