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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9B249C77B75 for ; Wed, 17 May 2023 15:00:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=bgoYFXMO7I9ICIbtmb2LUw5H3NGWuNq84hZjAo+clQQ=; b=s8XZ5hCt2UtlKl dpFtaYfBWQpkvTjsHnXLTb7UdsB4MEbAF9tct8x7HOHN0Wci1ERVFzOYvw7OljQdiIBDRhLwmYA3z bH9W4MiEcfa4Xz0GC8jkcFJtA6ScPNnOkVy8grIEiR2phWb6QC/B0qDQfeiSk1m/cPYPokHrZx6Kt 1Oa/AEf5otvwGZSeIWWkpvlUZ2HcdVUGXYx4hsjTpDRwnOzDf42NGwZezvDeSRjPigqNKbI7ppmi3 39HfuZIXzZBXxbNhbc4LcKRd0nBRQV7uGDQqrwdGmAKjt58k+TSAembOjN3woCpjiMimZgucD/uUB S62zkUyS6+vhkfGvaKuw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1pzIdF-00AE2f-1Y; Wed, 17 May 2023 15:00:01 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1pzIdA-00ADzT-29 for linux-arm-kernel@lists.infradead.org; Wed, 17 May 2023 14:59:59 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6E33C113E; Wed, 17 May 2023 08:00:38 -0700 (PDT) Received: from [10.57.58.217] (unknown [10.57.58.217]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A69203F73F; Wed, 17 May 2023 07:59:50 -0700 (PDT) Message-ID: <993ee407-cd7a-ab14-9d66-2e1009e05d3a@arm.com> Date: Wed, 17 May 2023 15:59:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH v3 3/3] arm64: mte: Simplify swap tag restoration logic Content-Language: en-GB To: Peter Collingbourne , Catalin Marinas Cc: =?UTF-8?B?UXVuLXdlaSBMaW4gKOael+e+pOW0tCk=?= , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "surenb@google.com" , "david@redhat.com" , =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= , "kasan-dev@googlegroups.com" , =?UTF-8?B?S3Vhbi1ZaW5nIExlZSAo5p2O5Yag56mOKQ==?= , =?UTF-8?B?Q2FzcGVyIExpICjmnY7kuK3mpq4p?= , "gregkh@linuxfoundation.org" , vincenzo.frascino@arm.com, Alexandru Elisei , will@kernel.org, eugenis@google.com References: <20230517022115.3033604-1-pcc@google.com> <20230517022115.3033604-4-pcc@google.com> From: Steven Price In-Reply-To: <20230517022115.3033604-4-pcc@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230517_075956_830364_260E9B0E X-CRM114-Status: GOOD ( 30.14 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 17/05/2023 03:21, Peter Collingbourne wrote: > As a result of the previous two patches, there are no circumstances > in which a swapped-in page is installed in a page table without first > having arch_swap_restore() called on it. Therefore, we no longer need > the logic in set_pte_at() that restores the tags, so remove it. > > Because we can now rely on the page being locked, we no longer need to > handle the case where a page is having its tags restored by multiple tasks > concurrently, so we can slightly simplify the logic in mte_restore_tags(). > > Signed-off-by: Peter Collingbourne > Link: https://linux-review.googlesource.com/id/I8ad54476f3b2d0144ccd8ce0c1d7a2963e5ff6f3 This is much neater, thanks for figuring out a better way of implementing it. The set_pte_at() thing always felt like a hack, but it was always there for the non-swap case and I obviously never figured out a better solution. Reviewed-by: Steven Price > --- > v3: > - Rebased onto arm64/for-next/fixes, which already has a fix > for the issue previously tagged, therefore removed Fixes: > tag > > arch/arm64/include/asm/mte.h | 4 ++-- > arch/arm64/include/asm/pgtable.h | 14 ++---------- > arch/arm64/kernel/mte.c | 37 ++++++-------------------------- > arch/arm64/mm/mteswap.c | 7 +++--- > 4 files changed, 14 insertions(+), 48 deletions(-) > > diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h > index c028afb1cd0b..4cedbaa16f41 100644 > --- a/arch/arm64/include/asm/mte.h > +++ b/arch/arm64/include/asm/mte.h > @@ -90,7 +90,7 @@ static inline bool try_page_mte_tagging(struct page *page) > } > > void mte_zero_clear_page_tags(void *addr); > -void mte_sync_tags(pte_t old_pte, pte_t pte); > +void mte_sync_tags(pte_t pte); > void mte_copy_page_tags(void *kto, const void *kfrom); > void mte_thread_init_user(void); > void mte_thread_switch(struct task_struct *next); > @@ -122,7 +122,7 @@ static inline bool try_page_mte_tagging(struct page *page) > static inline void mte_zero_clear_page_tags(void *addr) > { > } > -static inline void mte_sync_tags(pte_t old_pte, pte_t pte) > +static inline void mte_sync_tags(pte_t pte) > { > } > static inline void mte_copy_page_tags(void *kto, const void *kfrom) > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 0bd18de9fd97..e8a252e62b12 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -337,18 +337,8 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr, > * don't expose tags (instruction fetches don't check tags). > */ > if (system_supports_mte() && pte_access_permitted(pte, false) && > - !pte_special(pte)) { > - pte_t old_pte = READ_ONCE(*ptep); > - /* > - * We only need to synchronise if the new PTE has tags enabled > - * or if swapping in (in which case another mapping may have > - * set tags in the past even if this PTE isn't tagged). > - * (!pte_none() && !pte_present()) is an open coded version of > - * is_swap_pte() > - */ > - if (pte_tagged(pte) || (!pte_none(old_pte) && !pte_present(old_pte))) > - mte_sync_tags(old_pte, pte); > - } > + !pte_special(pte) && pte_tagged(pte)) > + mte_sync_tags(pte); > > __check_safe_pte_update(mm, ptep, pte); > > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index 7e89968bd282..c40728046fed 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -35,41 +35,18 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode); > EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode); > #endif > > -static void mte_sync_page_tags(struct page *page, pte_t old_pte, > - bool check_swap, bool pte_is_tagged) > -{ > - if (check_swap && is_swap_pte(old_pte)) { > - swp_entry_t entry = pte_to_swp_entry(old_pte); > - > - if (!non_swap_entry(entry)) > - mte_restore_tags(entry, page); > - } > - > - if (!pte_is_tagged) > - return; > - > - if (try_page_mte_tagging(page)) { > - mte_clear_page_tags(page_address(page)); > - set_page_mte_tagged(page); > - } > -} > - > -void mte_sync_tags(pte_t old_pte, pte_t pte) > +void mte_sync_tags(pte_t pte) > { > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > - bool check_swap = nr_pages == 1; > - bool pte_is_tagged = pte_tagged(pte); > - > - /* Early out if there's nothing to do */ > - if (!check_swap && !pte_is_tagged) > - return; > > /* if PG_mte_tagged is set, tags have already been initialised */ > - for (i = 0; i < nr_pages; i++, page++) > - if (!page_mte_tagged(page)) > - mte_sync_page_tags(page, old_pte, check_swap, > - pte_is_tagged); > + for (i = 0; i < nr_pages; i++, page++) { > + if (try_page_mte_tagging(page)) { > + mte_clear_page_tags(page_address(page)); > + set_page_mte_tagged(page); > + } > + } > > /* ensure the tags are visible before the PTE is set */ > smp_wmb(); > diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c > index cd508ba80ab1..3a78bf1b1364 100644 > --- a/arch/arm64/mm/mteswap.c > +++ b/arch/arm64/mm/mteswap.c > @@ -53,10 +53,9 @@ void mte_restore_tags(swp_entry_t entry, struct page *page) > if (!tags) > return; > > - if (try_page_mte_tagging(page)) { > - mte_restore_page_tags(page_address(page), tags); > - set_page_mte_tagged(page); > - } > + WARN_ON_ONCE(!try_page_mte_tagging(page)); > + mte_restore_page_tags(page_address(page), tags); > + set_page_mte_tagged(page); > } > > void mte_invalidate_tags(int type, pgoff_t offset) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel