From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AAAE12C21EA for ; Thu, 27 Nov 2025 05:41:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764222092; cv=none; b=iKhRIBw4hzR/gVmOC/wglIt7ioYIjx1avlDW3cVMZOPEDoMIDuFBwv4TF2eo1lUCEgRWeJTipYsDEEGlSEzm9Xp1LO0kxOm97jR4YtR9ln66flvrCIrlX/I/xRxIqnVgSu+8c+zIBWETnUUIs/jN/dcXPuZLYbcfRTS9W/45jbE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764222092; c=relaxed/simple; bh=nk+BGNbENl7c6f97a/IQX48zEfcoWKd4PDj6NN4FHZE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ITqV77IIWMqCal1ljOqp352lwHWxuduZOStz4ihWj5Qcwrh59i1xpHAGG0Jcbv8vTWpLZ1aDMtioRb/RwzE2z67/ncOxa+d0+B1QS7smJeFjpoWeKrihwRXh1O9/3UvGWn/Ups0lGGroS/3riIW1XwJcLcKezxy0W4EbXU02DTc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 027EC1477; Wed, 26 Nov 2025 21:41:22 -0800 (PST) Received: from [10.163.48.177] (unknown [10.163.48.177]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B54343F66E; Wed, 26 Nov 2025 21:41:26 -0800 (PST) Message-ID: Date: Thu, 27 Nov 2025 11:11:20 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: mm: Fix kexec failure after pte_mkwrite_novma() change To: Jianpeng Chang , catalin.marinas@arm.com, will@kernel.org, ardb@kernel.org, ying.huang@linux.alibaba.com Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20251127034350.3600454-1-jianpeng.chang.cn@windriver.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <20251127034350.3600454-1-jianpeng.chang.cn@windriver.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 27/11/25 9:13 AM, Jianpeng Chang wrote: > Commit 143937ca51cc ("arm64, mm: avoid always making PTE dirty in > pte_mkwrite()") modified pte_mkwrite_novma() to only clear PTE_RDONLY > when the page is already dirty (PTE_DIRTY is set). While this optimization > prevents unnecessary dirty page marking in normal memory management paths, > it breaks kexec on some platforms like NXP LS1043. > > The issue occurs in the kexec code path: > 1. machine_kexec_post_load() calls trans_pgd_create_copy() to create a > writable copy of the linear mapping > 2. _copy_pte() calls pte_mkwrite_novma() to ensure all pages in the copy > are writable for the new kernel image copying > 3. With the new logic, clean pages (without PTE_DIRTY) remain read-only > 4. When kexec tries to copy the new kernel image through the linear > mapping, it fails on read-only pages, causing the system to hang > after "Bye!" > > The same issue affects hibernation which uses the same trans_pgd code path. > > Fix this by explicitly clearing PTE_RDONLY in _copy_pte() for both > kexec and hibernation, ensuring all pages in the temporary mapping are > writable regardless of their dirty state. This preserves the original > commit's optimization for normal memory management while fixing the > kexec/hibernation regression. > > Fixes: 143937ca51cc ("arm64, mm: avoid always making PTE dirty in pte_mkwrite()") > Signed-off-by: Jianpeng Chang > --- > arch/arm64/mm/trans_pgd.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c > index 18543b603c77..ad4e5e4fcc91 100644 > --- a/arch/arm64/mm/trans_pgd.c > +++ b/arch/arm64/mm/trans_pgd.c > @@ -40,8 +40,13 @@ static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr) > * Resume will overwrite areas that may be marked > * read only (code, rodata). Clear the RDONLY bit from > * the temporary mappings we use during restore. > + * > + * For kexec/hibernation, we need writable access regardless > + * of the page's dirty state, so force clear PTE_RDONLY. > */ Hence pte_mkwrite_novma() helper cannot be used here as would have normally expected. Might be good idea to add to the above comment. > - __set_pte(dst_ptep, pte_mkwrite_novma(pte)); > + pte = set_pte_bit(pte, __pgprot(PTE_WRITE)); > + pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY)); > + __set_pte(dst_ptep, pte); > } else if (!pte_none(pte)) { > /* > * debug_pagealloc will removed the PTE_VALID bit if > @@ -57,7 +62,10 @@ static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr) > */ > BUG_ON(!pfn_valid(pte_pfn(pte))); > > - __set_pte(dst_ptep, pte_mkvalid(pte_mkwrite_novma(pte))); > + pte = pte_mkvalid(pte); Probably better to move pte_mkvalid() just after clearing PTE_RDONLY. > + pte = set_pte_bit(pte, __pgprot(PTE_WRITE)); > + pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY)); > + __set_pte(dst_ptep, pte); > } > } > Just wondering if it would be worth adding a local helper for the set PTE_WRITE --> clear PTR_RDONLY sequence describing its difference with now updated pte_mkwrite_novma() helper with the earlier comment.