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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 AE520C43461 for ; Tue, 15 Sep 2020 17:42:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 583D120936 for ; Tue, 15 Sep 2020 17:42:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600191749; bh=Wut+/LKuurJjV6yWdQ0LkAiD7T7c8wwiKIpWcqWDTyQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=TujMjvYkjfq13GV6Jq/PlwPD3b851f/GsRG7jCU0TCVH1w73zM7hB4UHsvNmrH+t7 cxgxeMw6V/JRmjsxf+qkLZARrAbK2Q8amTPyWOVIPmcCvE0IV6oqLjqqjesJOtP+WC A5Y947zV5lG9RrTaKknzrNCPxBA9X6aTyG5R0ePs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727895AbgIORmZ (ORCPT ); Tue, 15 Sep 2020 13:42:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:51006 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727753AbgIORSj (ORCPT ); Tue, 15 Sep 2020 13:18:39 -0400 Received: from kernel.org (unknown [87.71.73.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 33F3520872; Tue, 15 Sep 2020 17:18:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600190318; bh=Wut+/LKuurJjV6yWdQ0LkAiD7T7c8wwiKIpWcqWDTyQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YeUxScuVHsoRcQepFJGfs1FFAf2e1LA1+mSzjWkJRc8NB4Y0dZ0Yq79Hxs/lrBnxk pVbp2fKt9JCX5uVPX6sH97oaOJOt5ijiHPqC0TWMYPs7q/pJCrcD7UjG64D4R6O2M1 qX+5OQ6Q4SltpWyluJLoWn8FICTrQN6EcS6Jp4sg= Date: Tue, 15 Sep 2020 20:18:23 +0300 From: Mike Rapoport To: Vasily Gorbik Cc: Jason Gunthorpe , John Hubbard , Linus Torvalds , Gerald Schaefer , Alexander Gordeev , Peter Zijlstra , Dave Hansen , LKML , linux-mm , linux-arch , Andrew Morton , Russell King , Catalin Marinas , Will Deacon , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Jeff Dike , Richard Weinberger , Dave Hansen , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Arnd Bergmann , Andrey Ryabinin , linux-x86 , linux-arm , linux-power , linux-sparc , linux-um , linux-s390 , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda Subject: Re: [PATCH v2] mm/gup: fix gup_fast with dynamic page table folding Message-ID: <20200915171823.GJ2142832@kernel.org> References: <20200911200511.GC1221970@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 11, 2020 at 10:36:43PM +0200, Vasily Gorbik wrote: > Currently to make sure that every page table entry is read just once > gup_fast walks perform READ_ONCE and pass pXd value down to the next > gup_pXd_range function by value e.g.: > > static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, > unsigned int flags, struct page **pages, int *nr) > ... > pudp = pud_offset(&p4d, addr); > > This function passes a reference on that local value copy to pXd_offset, > and might get the very same pointer in return. This happens when the > level is folded (on most arches), and that pointer should not be iterated. > > On s390 due to the fact that each task might have different 5,4 or > 3-level address translation and hence different levels folded the logic > is more complex and non-iteratable pointer to a local copy leads to > severe problems. > > Here is an example of what happens with gup_fast on s390, for a task > with 3-levels paging, crossing a 2 GB pud boundary: > > // addr = 0x1007ffff000, end = 0x10080001000 > static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, > unsigned int flags, struct page **pages, int *nr) > { > unsigned long next; > pud_t *pudp; > > // pud_offset returns &p4d itself (a pointer to a value on stack) > pudp = pud_offset(&p4d, addr); > do { > // on second iteratation reading "random" stack value > pud_t pud = READ_ONCE(*pudp); > > // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 > next = pud_addr_end(addr, end); > ... > } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack > > return 1; > } > > This happens since s390 moved to common gup code with > commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") > and commit 1a42010cdc26 ("s390/mm: convert to the generic > get_user_pages_fast code"). s390 tried to mimic static level folding by > changing pXd_offset primitives to always calculate top level page table > offset in pgd_offset and just return the value passed when pXd_offset > has to act as folded. > > What is crucial for gup_fast and what has been overlooked is > that PxD_SIZE/MASK and thus pXd_addr_end should also change > correspondingly. And the latter is not possible with dynamic folding. > > To fix the issue in addition to pXd values pass original > pXdp pointers down to gup_pXd_range functions. And introduce > pXd_offset_lockless helpers, which take an additional pXd > entry value parameter. This has already been discussed in > https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 > > Cc: # 5.2+ > Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") > Reviewed-by: Gerald Schaefer > Reviewed-by: Alexander Gordeev > Signed-off-by: Vasily Gorbik Reviewed-by: Mike Rapoport > --- > v2: added brackets &pgd -> &(pgd) > > arch/s390/include/asm/pgtable.h | 42 +++++++++++++++++++++++---------- > include/linux/pgtable.h | 10 ++++++++ > mm/gup.c | 18 +++++++------- > 3 files changed, 49 insertions(+), 21 deletions(-) > > diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h > index 7eb01a5459cd..b55561cc8786 100644 > --- a/arch/s390/include/asm/pgtable.h > +++ b/arch/s390/include/asm/pgtable.h > @@ -1260,26 +1260,44 @@ static inline pgd_t *pgd_offset_raw(pgd_t *pgd, unsigned long address) > > #define pgd_offset(mm, address) pgd_offset_raw(READ_ONCE((mm)->pgd), address) > > -static inline p4d_t *p4d_offset(pgd_t *pgd, unsigned long address) > +static inline p4d_t *p4d_offset_lockless(pgd_t *pgdp, pgd_t pgd, unsigned long address) > { > - if ((pgd_val(*pgd) & _REGION_ENTRY_TYPE_MASK) >= _REGION_ENTRY_TYPE_R1) > - return (p4d_t *) pgd_deref(*pgd) + p4d_index(address); > - return (p4d_t *) pgd; > + if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) >= _REGION_ENTRY_TYPE_R1) > + return (p4d_t *) pgd_deref(pgd) + p4d_index(address); > + return (p4d_t *) pgdp; > } > +#define p4d_offset_lockless p4d_offset_lockless > > -static inline pud_t *pud_offset(p4d_t *p4d, unsigned long address) > +static inline p4d_t *p4d_offset(pgd_t *pgdp, unsigned long address) > { > - if ((p4d_val(*p4d) & _REGION_ENTRY_TYPE_MASK) >= _REGION_ENTRY_TYPE_R2) > - return (pud_t *) p4d_deref(*p4d) + pud_index(address); > - return (pud_t *) p4d; > + return p4d_offset_lockless(pgdp, *pgdp, address); > +} > + > +static inline pud_t *pud_offset_lockless(p4d_t *p4dp, p4d_t p4d, unsigned long address) > +{ > + if ((p4d_val(p4d) & _REGION_ENTRY_TYPE_MASK) >= _REGION_ENTRY_TYPE_R2) > + return (pud_t *) p4d_deref(p4d) + pud_index(address); > + return (pud_t *) p4dp; > +} > +#define pud_offset_lockless pud_offset_lockless > + > +static inline pud_t *pud_offset(p4d_t *p4dp, unsigned long address) > +{ > + return pud_offset_lockless(p4dp, *p4dp, address); > } > #define pud_offset pud_offset > > -static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address) > +static inline pmd_t *pmd_offset_lockless(pud_t *pudp, pud_t pud, unsigned long address) > +{ > + if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) >= _REGION_ENTRY_TYPE_R3) > + return (pmd_t *) pud_deref(pud) + pmd_index(address); > + return (pmd_t *) pudp; > +} > +#define pmd_offset_lockless pmd_offset_lockless > + > +static inline pmd_t *pmd_offset(pud_t *pudp, unsigned long address) > { > - if ((pud_val(*pud) & _REGION_ENTRY_TYPE_MASK) >= _REGION_ENTRY_TYPE_R3) > - return (pmd_t *) pud_deref(*pud) + pmd_index(address); > - return (pmd_t *) pud; > + return pmd_offset_lockless(pudp, *pudp, address); > } > #define pmd_offset pmd_offset > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index e8cbc2e795d5..90654cb63e9e 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -1427,6 +1427,16 @@ typedef unsigned int pgtbl_mod_mask; > #define mm_pmd_folded(mm) __is_defined(__PAGETABLE_PMD_FOLDED) > #endif > > +#ifndef p4d_offset_lockless > +#define p4d_offset_lockless(pgdp, pgd, address) p4d_offset(&(pgd), address) > +#endif > +#ifndef pud_offset_lockless > +#define pud_offset_lockless(p4dp, p4d, address) pud_offset(&(p4d), address) > +#endif > +#ifndef pmd_offset_lockless > +#define pmd_offset_lockless(pudp, pud, address) pmd_offset(&(pud), address) > +#endif > + > /* > * p?d_leaf() - true if this entry is a final mapping to a physical address. > * This differs from p?d_huge() by the fact that they are always available (if > diff --git a/mm/gup.c b/mm/gup.c > index e5739a1974d5..578bf5bd8bf8 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2485,13 +2485,13 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, > return 1; > } > > -static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, > +static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned long end, > unsigned int flags, struct page **pages, int *nr) > { > unsigned long next; > pmd_t *pmdp; > > - pmdp = pmd_offset(&pud, addr); > + pmdp = pmd_offset_lockless(pudp, pud, addr); > do { > pmd_t pmd = READ_ONCE(*pmdp); > > @@ -2528,13 +2528,13 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, > return 1; > } > > -static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, > +static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned long end, > unsigned int flags, struct page **pages, int *nr) > { > unsigned long next; > pud_t *pudp; > > - pudp = pud_offset(&p4d, addr); > + pudp = pud_offset_lockless(p4dp, p4d, addr); > do { > pud_t pud = READ_ONCE(*pudp); > > @@ -2549,20 +2549,20 @@ static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, > if (!gup_huge_pd(__hugepd(pud_val(pud)), addr, > PUD_SHIFT, next, flags, pages, nr)) > return 0; > - } else if (!gup_pmd_range(pud, addr, next, flags, pages, nr)) > + } else if (!gup_pmd_range(pudp, pud, addr, next, flags, pages, nr)) > return 0; > } while (pudp++, addr = next, addr != end); > > return 1; > } > > -static int gup_p4d_range(pgd_t pgd, unsigned long addr, unsigned long end, > +static int gup_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, unsigned long end, > unsigned int flags, struct page **pages, int *nr) > { > unsigned long next; > p4d_t *p4dp; > > - p4dp = p4d_offset(&pgd, addr); > + p4dp = p4d_offset_lockless(pgdp, pgd, addr); > do { > p4d_t p4d = READ_ONCE(*p4dp); > > @@ -2574,7 +2574,7 @@ static int gup_p4d_range(pgd_t pgd, unsigned long addr, unsigned long end, > if (!gup_huge_pd(__hugepd(p4d_val(p4d)), addr, > P4D_SHIFT, next, flags, pages, nr)) > return 0; > - } else if (!gup_pud_range(p4d, addr, next, flags, pages, nr)) > + } else if (!gup_pud_range(p4dp, p4d, addr, next, flags, pages, nr)) > return 0; > } while (p4dp++, addr = next, addr != end); > > @@ -2602,7 +2602,7 @@ static void gup_pgd_range(unsigned long addr, unsigned long end, > if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, > PGDIR_SHIFT, next, flags, pages, nr)) > return; > - } else if (!gup_p4d_range(pgd, addr, next, flags, pages, nr)) > + } else if (!gup_p4d_range(pgdp, pgd, addr, next, flags, pages, nr)) > return; > } while (pgdp++, addr = next, addr != end); > } > -- > ⣿⣿⣿⣿⢋⡀⣀⠹⣿⣿⣿⣿ > ⣿⣿⣿⣿⠠⣶⡦⠀⣿⣿⣿⣿ > ⣿⣿⣿⠏⣴⣮⣴⣧⠈⢿⣿⣿ > ⣿⣿⡏⢰⣿⠖⣠⣿⡆⠈⣿⣿ > ⣿⢛⣵⣄⠙⣶⣶⡟⣅⣠⠹⣿ > ⣿⣜⣛⠻⢎⣉⣉⣀⠿⣫⣵⣿ -- Sincerely yours, Mike.