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 9D88F2F691B; Tue, 4 Nov 2025 13:22:55 +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=1762262577; cv=none; b=p5wvNTWY18mB5yPzNzfddO6vZKAofyZ+VgOX7JSraTq8VKpQ49zO8HGfJSlTqqUiHLmSO8s9vNmzW8bhgF14s2tyEFlhBORDA5joV/qhYQnPGnY2PHrnQFnIS8LUKdJ7Kn/POTzx9EZuQ6hKVfmf3XfB0wchTiuGDIRYumXalCA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762262577; c=relaxed/simple; bh=w1EXmzaomt43Vs7KKsVgrSwxeKJ4lAKIlz7ba/TQnoc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=TfGi8IPEhrlPk9tfJTqoPRaEyHG6LzQyUYXLvT+9qr3/719QciST2wIoL318YPGDfOcVH0aEFy/ube4IF3iTL1r0uzLLTHu5gCtfgfYuw4v5bBdMBYshk4IceRDcHFb5r2vL5ThG/GIo2p5wAl7tH8Osgylcxa/hADF0cPp55NQ= 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 3B4EB1CE0; Tue, 4 Nov 2025 05:22:47 -0800 (PST) Received: from [10.164.18.64] (unknown [10.164.18.64]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 225613F66E; Tue, 4 Nov 2025 05:22:51 -0800 (PST) Message-ID: <9f55664b-c510-4565-943b-0bed2d43898d@arm.com> Date: Tue, 4 Nov 2025 18:52:49 +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/pageattr: Propagate return value from __change_memory_common To: Will Deacon Cc: Yang Shi , catalin.marinas@arm.com, ryan.roberts@arm.com, rppt@kernel.org, shijie@os.amperecomputing.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20251103061306.82034-1-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 04/11/25 6:26 pm, Will Deacon wrote: > On Tue, Nov 04, 2025 at 09:06:12AM +0530, Dev Jain wrote: >> On 04/11/25 12:15 am, Yang Shi wrote: >>> On 11/3/25 7:16 AM, Will Deacon wrote: >>>> On Mon, Nov 03, 2025 at 11:43:06AM +0530, Dev Jain wrote: >>>>> Post a166563e7ec3 ("arm64: mm: support large block mapping when >>>>> rodata=full"), >>>>> __change_memory_common has a real chance of failing due to split >>>>> failure. >>>>> Before that commit, this line was introduced in c55191e96caa, >>>>> still having >>>>> a chance of failing if it needs to allocate pagetable memory in >>>>> apply_to_page_range, although that has never been observed to be true. >>>>> In general, we should always propagate the return value to the caller. >>>>> >>>>> Cc: stable@vger.kernel.org >>>>> Fixes: c55191e96caa ("arm64: mm: apply r/o permissions of VM >>>>> areas to its linear alias as well") >>>>> Signed-off-by: Dev Jain >>>>> --- >>>>> Based on Linux 6.18-rc4. >>>>> >>>>>   arch/arm64/mm/pageattr.c | 5 ++++- >>>>>   1 file changed, 4 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c >>>>> index 5135f2d66958..b4ea86cd3a71 100644 >>>>> --- a/arch/arm64/mm/pageattr.c >>>>> +++ b/arch/arm64/mm/pageattr.c >>>>> @@ -148,6 +148,7 @@ static int change_memory_common(unsigned >>>>> long addr, int numpages, >>>>>       unsigned long size = PAGE_SIZE * numpages; >>>>>       unsigned long end = start + size; >>>>>       struct vm_struct *area; >>>>> +    int ret; >>>>>       int i; >>>>>         if (!PAGE_ALIGNED(addr)) { >>>>> @@ -185,8 +186,10 @@ static int change_memory_common(unsigned >>>>> long addr, int numpages, >>>>>       if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY || >>>>>                   pgprot_val(clear_mask) == PTE_RDONLY)) { >>>>>           for (i = 0; i < area->nr_pages; i++) { >>>>> - __change_memory_common((u64)page_address(area->pages[i]), >>>>> +            ret = >>>>> __change_memory_common((u64)page_address(area->pages[i]), >>>>>                              PAGE_SIZE, set_mask, clear_mask); >>>>> +            if (ret) >>>>> +                return ret; >>>> Hmm, this means we can return failure half-way through the operation. Is >>>> that something callers are expecting to handle? If so, how can they tell >>>> how far we got? >>> IIUC the callers don't have to know whether it is half-way or not >>> because the callers will change the permission back (e.g. to RW) for the >>> whole range when freeing memory. >> Yes, it is the caller's responsibility to set VM_FLUSH_RESET_PERMS flag. >> Upon vfree(), it will change the direct map permissions back to RW. > Ok, but vfree() ends up using update_range_prot() to do that and if we > need to worry about that failing (as per your commit message), then > we're in trouble because the calls to set_area_direct_map() are unchecked. > > In other words, this patch is either not necessary or it is incomplete. I think we had concluded in the discussion of the linear map series that those calls will always succeed - I'll refresh my memory on that and get back to you later! > > Will