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 E74561E832A for ; Wed, 3 Dec 2025 07:07:59 +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=1764745682; cv=none; b=e+3xinXpsiCtc6eAL7y4P+z2VvM1Tf6tstbR1UHU/42eKOXnfi7ng6g6RItXN6wOCzAWUGr7bAJ+54jUHUDgcsZ8Hip1FNwMYvkCzmNJR3v7dll6xTVXrLS3cgzZ32mRzZ/Ygji0M7WbC2xeIpsCT0oQ2/eWtTzwvuwSEWI+0ow= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764745682; c=relaxed/simple; bh=2NNStnlqEJHLzzZUCya4VlhNXnvZKJe9RpBhkKY00bE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qAEXxD4Qv9si8xuSN6fF2SnVxyAkXjkb10zoF8+jfNZ5ia5XlmfY/cvnePKLHPTPXtsh5GwG3jttskYx1uk+xBsUnO82wMueTP6v9Bae69ub8znfafCn9/ZYIntml2grz3OzMATtesn4Sq8bQqgAy7d04HQ00rCRaWigE/WcwA0= 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 67AA8339; Tue, 2 Dec 2025 23:07:46 -0800 (PST) Received: from [10.163.49.22] (unknown [10.163.49.22]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 91BC43F59E; Tue, 2 Dec 2025 23:07:51 -0800 (PST) Message-ID: <296f9c4b-8c93-4464-9b75-e06770a4bd31@arm.com> Date: Wed, 3 Dec 2025 12:37:48 +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: [v2 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: <20251202022707.2720933-1-jianpeng.chang.cn@windriver.com> <381a3974-aafa-419f-a7ad-ed6e4c1671f0@arm.com> <58d796ec-b430-4fc0-9a1c-8f1a6150f051@windriver.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <58d796ec-b430-4fc0-9a1c-8f1a6150f051@windriver.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 02/12/25 1:25 PM, Jianpeng Chang wrote: > > On 12/2/25 2:57 PM, Anshuman Khandual wrote: >> CAUTION: This email comes from a non Wind River email account! >> Do not click links or open attachments unless you recognize the sender and know the content is safe. >> >> On 02/12/25 7:57 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 >> via pte_mkdirty() ? > Sorry, for this. > > Fix this by marking pages dirty with pte_mkdirty() in _copy_pte(), which > ensures pte_mkwrite_novma() clears PTE_RDONLY for both kexec and > hibernation, making all pages in the temporary mapping writable > regardless of their dirty state. Fair enough. >> >>> 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 >>> --- >>> v2: >>> - Use pte_mkwrite_novma(pte_mkdirty(pte)) instead of manual bit manipulation >>> - Updated comments to clarify pte_mkwrite_novma() alone cannot be used >>> v1: https://lore.kernel.org/all/20251127034350.3600454-1-jianpeng.chang.cn@windriver.com/ >>> >>> arch/arm64/mm/trans_pgd.c | 9 +++++++-- >>> 1 file changed, 7 insertions(+), 2 deletions(-) >>> >>> diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c >>> index 18543b603c77..08f5ee6643e1 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 to all >>> + * pages in the linear mapping to copy the new kernel image. >>> + * Mark pages dirty first to ensure pte_mkwrite_novma() >>> + * clears PTE_RDONLY. >>> */ >> /* >> * For both kexec and hibernation, writable accesses are required >> * for all pages in the linear map to copy over new kernel image. >> * Hence mark these pages dirty first via pte_mkdirty() to ensure >> * pte_mkwrite_novma() subsequently clears PTE_RDONLY - providing >> * required write access for the pages. >> */ > I will change it. >> >>> - __set_pte(dst_ptep, pte_mkwrite_novma(pte)); >>> + __set_pte(dst_ptep, pte_mkwrite_novma(pte_mkdirty(pte))); >>> } else if (!pte_none(pte)) { >>> /* >>> * debug_pagealloc will removed the PTE_VALID bit if >>> @@ -57,7 +62,7 @@ static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr) >>> */ >>> BUG_ON(!pfn_valid(pte_pfn(pte))); >>> >> The comments should be replicated here as well given the same special situation. > I will change it. >> >>> - __set_pte(dst_ptep, pte_mkvalid(pte_mkwrite_novma(pte))); >>> + __set_pte(dst_ptep, pte_mkvalid(pte_mkwrite_novma(pte_mkdirty(pte)))); >>> } >>> } >>> >> static inline pte_t pte_mkwrite_novma(pte_t pte) >> { >> pte = set_pte_bit(pte, __pgprot(PTE_WRITE)); >> if (pte_sw_dirty(pte)) >> pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY)); >> return pte; >> } >> >> static inline pte_t pte_mkdirty(pte_t pte) >> { >> pte = set_pte_bit(pte, __pgprot(PTE_DIRTY)); >> >> if (pte_write(pte)) >> pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY)); >> >> return pte; >> } >> >> So if pte_write() is true, there will be a redundant PTE_RDONLY clearing which is OK. >> Should this be mentioned in the commit message ? > TBH, I don't have a better idea - any suggestions? > > Or, let's add some lines: > > Using pte_mkdirty() causes redundant bit operations, but this is > acceptable since it's not a hot path. Makes sense - better to call out potential redundancies.