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 91591C4332F for ; Mon, 21 Nov 2022 12:29:00 +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:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=R9ywnGV8TnmyOjC3z53eVQpKxnha1zPa1Mu9tZRsyq8=; b=12AEa//bCZ6rm4 oUkSpGmuBYtr/jURed7sI5u/5T6sWtrlpUQ7snuuFfDqkmprechV03Lj3apOUy1TWqBXGz22ASfma fIrdvLwRodmYEC+BmiAJw+YALeDw147/k7rPssxNCVfny3UGNq/0nWZLndkXbPcb6PQgIIcsW+A2t GdmuTyzlBBV2fcxEZ85XVr6ryWJ83HyRm3x62T2Kcz9Mu+ROq5WpKmeFQCeqhLiJiiac51wUR+69B FstNpuaB61ITGveLXJ4+CjdhNsTPwkcijfdWDP+xDXGWFN56pZYPBk/6lpxD4XoX9P35ZDeMU9Gms KeSkl781G/VCr944pWfg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ox5u5-00DVz6-W3; Mon, 21 Nov 2022 12:28:02 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ox5u3-00DVxQ-1P for linux-arm-kernel@lists.infradead.org; Mon, 21 Nov 2022 12:28:00 +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 B8ACB23A; Mon, 21 Nov 2022 04:28:01 -0800 (PST) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.25.132]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 299953F7D8; Mon, 21 Nov 2022 04:27:54 -0800 (PST) Date: Mon, 21 Nov 2022 12:27:51 +0000 From: Mark Rutland To: Anshuman Khandual Cc: Nathan Chancellor , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Andrew Morton , linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH] arm64/mm: Drop redundant BUG_ON(!pgtable_alloc) Message-ID: References: <20221118053102.500216-1-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221121_042759_193670_FEE78B52 X-CRM114-Status: GOOD ( 30.36 ) 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, Nov 21, 2022 at 11:00:42AM +0530, Anshuman Khandual wrote: > Hello Nathan, > > Thanks for the report. > > On 11/20/22 21:46, Nathan Chancellor wrote: > > Hi Anshuman, > > I just bisected a boot failure in our QEMU-based continuous integration > > setup to this change as commit 9ed2b4616d4e ("arm64/mm: Drop redundant > > BUG_ON(!pgtable_alloc)") in the arm64 tree. There is no output so the > > panic clearly happens early at boot. If I move back to the previous > > commit and add a WARN_ON() like so: > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > > index d386033a074c..9280a92ff920 100644 > > --- a/arch/arm64/mm/mmu.c > > +++ b/arch/arm64/mm/mmu.c > > @@ -383,6 +383,7 @@ static void __create_pgd_mapping_locked(pgd_t *pgdir, phys_addr_t phys, > > phys &= PAGE_MASK; > > addr = virt & PAGE_MASK; > > end = PAGE_ALIGN(virt + size); > > + WARN_ON(!pgtable_alloc); > > > > do { > > next = pgd_addr_end(addr, end); > > > > I do see some stacktraces. I have attached the boot log from QEMU. > > > > If there is any additional information I can provide or patches I can > > test, I am more than happy to do so. > > There are couple of instances, where __create_pgd_mapping() function gets called > without a valid pgtable alloc function (NULL is passed on instead), as it is not > expected to allocate page table pages, during the mapping process. The following > change after this patch should solve the reported problem. > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 9ea8e9039992..a00563122fcb 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -42,6 +42,7 @@ > #define NO_BLOCK_MAPPINGS BIT(0) > #define NO_CONT_MAPPINGS BIT(1) > #define NO_EXEC_MAPPINGS BIT(2) /* assumes FEAT_HPDS is not used */ > +#define NO_ALLOC_MAPPINGS BIT(3) /* does not allocate page table pages */ > > int idmap_t0sz __ro_after_init; > > @@ -380,7 +381,7 @@ static void __create_pgd_mapping_locked(pgd_t *pgdir, phys_addr_t phys, > phys &= PAGE_MASK; > addr = virt & PAGE_MASK; > end = PAGE_ALIGN(virt + size); > - BUG_ON(!pgtable_alloc); > + BUG_ON(!(flags & NO_ALLOC_MAPPINGS) && !pgtable_alloc); > > do { > next = pgd_addr_end(addr, end); > @@ -453,7 +454,7 @@ static void __init create_mapping_noalloc(phys_addr_t phys, unsigned long virt, > return; > } > __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL, > - NO_CONT_MAPPINGS); > + NO_CONT_MAPPINGS | NO_ALLOC_MAPPINGS); > } > > void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys, > @@ -481,7 +482,7 @@ static void update_mapping_prot(phys_addr_t phys, unsigned long virt, > } > > __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL, > - NO_CONT_MAPPINGS); > + NO_CONT_MAPPINGS | NO_ALLOC_MAPPINGS); > > /* flush the TLBs after updating live kernel mappings */ > flush_tlb_kernel_range(virt, virt + size); This is now more complicated than what we had originally, and it doesn't catch the case where the caller sets NO_ALLOC_MAPPINGS but the callee ends up needing to perform an allocation, which the old code would have caught. This is clearly more subtle than we thought initially; for now could we please just drop the patch? Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel