From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH v5 06/25] mm: Add PG_ARCH_2 page flag Date: Wed, 24 Jun 2020 11:33:07 -0700 Message-ID: <20200624113307.6165b3db2404c9d37b870a90@linux-foundation.org> References: <20200624175244.25837-1-catalin.marinas@arm.com> <20200624175244.25837-7-catalin.marinas@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from mail.kernel.org ([198.145.29.99]:45040 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405820AbgFXSdJ (ORCPT ); Wed, 24 Jun 2020 14:33:09 -0400 In-Reply-To: <20200624175244.25837-7-catalin.marinas@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon , Dave P Martin , Vincenzo Frascino , Szabolcs Nagy , Kevin Brodsky , Andrey Konovalov , Peter Collingbourne , Steven Price On Wed, 24 Jun 2020 18:52:25 +0100 Catalin Marinas wrote: > From: Steven Price > > For arm64 MTE support it is necessary to be able to mark pages that > contain user space visible tags that will need to be saved/restored e.g. > when swapped out. > > To support this add a new arch specific flag (PG_ARCH_2) that arch code > can opt into using ARCH_USES_PG_ARCH_2. > > ... > > --- a/fs/proc/page.c > +++ b/fs/proc/page.c > @@ -217,6 +217,9 @@ u64 stable_page_flags(struct page *page) > u |= kpf_copy_bit(k, KPF_PRIVATE_2, PG_private_2); > u |= kpf_copy_bit(k, KPF_OWNER_PRIVATE, PG_owner_priv_1); > u |= kpf_copy_bit(k, KPF_ARCH, PG_arch_1); > +#ifdef CONFIG_ARCH_USES_PG_ARCH_2 > + u |= kpf_copy_bit(k, KPF_ARCH_2, PG_arch_2); > +#endif Do we need CONFIG_ARCH_USES_PG_ARCH_2? What would be the downside to giving every architecture a PG_arch_2, but only arm64 uses it (at present)?