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 5282523FC54 for ; Fri, 28 Nov 2025 04:34:05 +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=1764304447; cv=none; b=tz+2rPGmvkkeAdty1Dg7WU3hKkcvOrjp+80uMhIrVdrlqWViz8J8OmzU1tfFby6T0HvVRU+5AlGxKCyappnLyCt1QIIxEUR0g2nXHcUJWwqx7fY2Mj1KFNvzM0T1NSE7tBD7IE/RuP+6F2pHp3YlNXXPBokS52yDkNcn7eOvxMs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764304447; c=relaxed/simple; bh=T3m27R48qVkcj9dV+15P5ZyZgBnYuAkA/LjESmV62rI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VtBmJ6Z4n/RumLPmZRl0oiGW5qtBNzwlHfi0JzqoWwliw0qL+Tzme6ieRc3hW67vaRluKYOJ+Fmg1tB4mUxNA6fKK0TnNMo+oYts0b8/Z5Mt9nkJ31yFImSSxrQxCyd1YXdrjBkev5lMYljHDebiURC4ZgrpdmNUK6KhkFtBkNU= 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 17CA01575; Thu, 27 Nov 2025 20:33:57 -0800 (PST) Received: from [10.164.18.52] (unknown [10.164.18.52]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 849603F73B; Thu, 27 Nov 2025 20:34:02 -0800 (PST) Message-ID: Date: Fri, 28 Nov 2025 10:03:59 +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: "Chang, Jianpeng (CN)" , 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> <95c6e425-2436-42da-b408-4ec48752a2aa@windriver.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <95c6e425-2436-42da-b408-4ec48752a2aa@windriver.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 27/11/25 3:54 PM, Chang, Jianpeng (CN) wrote: > > On 11/27/2025 1:41 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 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. > I'll add this to make it clear that we can't use pte_mkwrite_novma(). >> >>> -             __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. > I'll make this change. >> >>> +             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. > > Thank you for the review! I appreciate your suggestions. > > You're right that a local helper would make the code more readable and clearly > > document the difference from pte_mkwrite_novma(). > > I have a small concern about placing PTE manipulation functions outside of > > pgtable.h - is this a good way? Or would you prefer this as a local static inline > > helper within trans_pgd.c given its specific use case for kexec/hibernation? A local static helper function in trans_pgd.c documenting the difference with standard pgtable helper pte_mkwrite_novma() would be better as it is not used else where. > > > I'll implement whichever approach you think is more appropriate in v2. > Let's wait some more time for other opinions as well. > > Best regards, > > Jianpeng >