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 CD498C282EC for ; Tue, 18 Mar 2025 11:19:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Vj4pnAv1lJriMVGawRz5JjDM9OZDa0vt2boAwaSGN9M=; b=w6VegEJeigmi5jSSgpsZ0lX7nn 14x1QBmrx7kLnWh6AjONFuvfFArhpVpaayiVE3SuSiFLZaXO1L+WWlfDHMe5rdcM2lxpTyXEUUGYX ++BoRJBfDADAP7JRq1AlxWolf9QuGkF6ZK0+7pVm6Ctc3CsfKfznWsLVUeDgWCpn3y281kWhQB7+x NH5uG0ZkeMkyLfIuDUj8yv6iNyesWtaID5JqaraaRmYInNXcu1J4s3T5+seSZWQabStYmQah5UlY6 UypKtx6CTar9eiQDE0KUVTIm7CiS1r88gr7qzZNHhNHXon7Pi9TxGxqm5hTQOGEeLIoHIvBwGSoJ6 JyCG0z9Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tuUyM-00000005h9z-35H7; Tue, 18 Mar 2025 11:19:02 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tuUwP-00000005gTK-1Qh5 for linux-arm-kernel@lists.infradead.org; Tue, 18 Mar 2025 11:17:02 +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 2685113D5; Tue, 18 Mar 2025 04:17:09 -0700 (PDT) Received: from J2N7QTR9R3 (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6A6BC3F694; Tue, 18 Mar 2025 04:16:59 -0700 (PDT) Date: Tue, 18 Mar 2025 11:16:54 +0000 From: Mark Rutland To: Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Ard Biesheuvel , Ryan Roberts , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] arm64/mm/hotplug: Drop redundant [pgd|p4d]_present() Message-ID: References: <20250221094449.1188427-1-anshuman.khandual@arm.com> <20250221094449.1188427-2-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250221094449.1188427-2-anshuman.khandual@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250318_041701_458295_4DF6DEA3 X-CRM114-Status: GOOD ( 15.56 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Feb 21, 2025 at 03:14:48PM +0530, Anshuman Khandual wrote: > [pgd|p4d]_present() are inverse to their corresponding [pgd|p4d]_none(). Maybe their implementations happen to be inverse today, but the semantic of pXX_present() is not the inverse of the semantic of pXX_none(). In general, !pXX_none() does not imply pXX_present(). > So [pgd|p4d]_present() test right after corresponding [pgd|p4d]_none() > inverse test does not make sense. Hence just drop these redundant > checks. I think the checks make sense in abstract, even if they're redundant today Is there any reason to remove these specific case? Surely the compiler optimizes these out when they're redundant? Mark. > > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Ard Biesheuvel > Cc: Ryan Roberts > Cc: Mark Rutland > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual > --- > arch/arm64/mm/mmu.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index b4df5bc5b1b8..66906c45c7f6 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -952,7 +952,6 @@ static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsigned long addr, > if (p4d_none(p4d)) > continue; > > - WARN_ON(!p4d_present(p4d)); > unmap_hotplug_pud_range(p4dp, addr, next, free_mapped, altmap); > } while (addr = next, addr < end); > } > @@ -978,7 +977,6 @@ static void unmap_hotplug_range(unsigned long addr, unsigned long end, > if (pgd_none(pgd)) > continue; > > - WARN_ON(!pgd_present(pgd)); > unmap_hotplug_p4d_range(pgdp, addr, next, free_mapped, altmap); > } while (addr = next, addr < end); > } > @@ -1114,7 +1112,6 @@ static void free_empty_p4d_table(pgd_t *pgdp, unsigned long addr, > if (p4d_none(p4d)) > continue; > > - WARN_ON(!p4d_present(p4d)); > free_empty_pud_table(p4dp, addr, next, floor, ceiling); > } while (addr = next, addr < end); > > @@ -1153,7 +1150,6 @@ static void free_empty_tables(unsigned long addr, unsigned long end, > if (pgd_none(pgd)) > continue; > > - WARN_ON(!pgd_present(pgd)); > free_empty_p4d_table(pgdp, addr, next, floor, ceiling); > } while (addr = next, addr < end); > } > -- > 2.30.2 >