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Mon, 17 May 2021 16:14:52 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (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 C97A360E0B; Mon, 17 May 2021 16:14:49 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1liftH-001tNE-NC; Mon, 17 May 2021 17:14:47 +0100 Date: Mon, 17 May 2021 17:14:46 +0100 Message-ID: <87y2cdtk09.wl-maz@kernel.org> From: Marc Zyngier To: Steven Price Cc: Catalin Marinas , Will Deacon , James Morse , Julien Thierry , Suzuki K Poulose , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave Martin , Mark Rutland , Thomas Gleixner , qemu-devel@nongnu.org, Juan Quintela , "Dr. David Alan Gilbert" , Richard Henderson , Peter Maydell , Haibo Xu , Andrew Jones Subject: Re: [PATCH v12 3/8] arm64: mte: Sync tags for pages where PTE is untagged In-Reply-To: <20210517123239.8025-4-steven.price@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-4-steven.price@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave.Martin@arm.com, mark.rutland@arm.com, tglx@linutronix.de, qemu-devel@nongnu.org, quintela@redhat.com, dgilbert@redhat.com, richard.henderson@linaro.org, peter.maydell@linaro.org, Haibo.Xu@arm.com, drjones@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210517_091451_261261_A35ECC56 X-CRM114-Status: GOOD ( 32.13 ) 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 Mon, 17 May 2021 13:32:34 +0100, Steven Price wrote: > > A KVM guest could store tags in a page even if the VMM hasn't mapped > the page with PROT_MTE. So when restoring pages from swap we will > need to check to see if there are any saved tags even if !pte_tagged(). > > However don't check pages for which pte_access_permitted() returns false > as these will not have been swapped out. > > Signed-off-by: Steven Price > --- > arch/arm64/include/asm/pgtable.h | 9 +++++++-- > arch/arm64/kernel/mte.c | 16 ++++++++++++++-- > 2 files changed, 21 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 0b10204e72fc..275178a810c1 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -314,8 +314,13 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, > if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte)) > __sync_icache_dcache(pte); > > - if (system_supports_mte() && > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte)) > + /* > + * If the PTE would provide user space access to the tags associated > + * with it then ensure that the MTE tags are synchronised. Exec-only > + * mappings don't expose tags (instruction fetches don't check tags). I'm not sure I understand this comment. Of course, execution doesn't match tags. But the memory could still have tags associated with it. Does this mean such a page would lose its tags is swapped out? Thanks, M. > + */ > + if (system_supports_mte() && pte_present(pte) && > + pte_access_permitted(pte, false) && !pte_special(pte)) > mte_sync_tags(ptep, pte); > > __check_racy_pte_update(mm, ptep, pte); > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index c88e778c2fa9..a604818c52c1 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -33,11 +33,15 @@ DEFINE_STATIC_KEY_FALSE(mte_async_mode); > EXPORT_SYMBOL_GPL(mte_async_mode); > #endif > > -static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > +static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap, > + bool pte_is_tagged) > { > unsigned long flags; > pte_t old_pte = READ_ONCE(*ptep); > > + if (!is_swap_pte(old_pte) && !pte_is_tagged) > + return; > + > spin_lock_irqsave(&tag_sync_lock, flags); > > /* Recheck with the lock held */ > @@ -53,6 +57,9 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > } > } > > + if (!pte_is_tagged) > + goto out; > + > page_kasan_tag_reset(page); > /* > * We need smp_wmb() in between setting the flags and clearing the > @@ -76,10 +83,15 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > 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 (!test_bit(PG_mte_tagged, &page->flags)) > - mte_sync_page_tags(page, ptep, check_swap); > + mte_sync_page_tags(page, ptep, check_swap, > + pte_is_tagged); > } > } > > -- > 2.20.1 > > -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel