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 A9E03CCFA04 for ; Tue, 4 Nov 2025 13:23:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=SmmRjIkYOPEXfWQtW27oBnH3jfo7JHhENvMCdY9nzZ4=; b=x5U+PgL2T6Tq1y3oXPPfbZ3Jim FfmfXaS/m4sgi4h+TCFcREeR2sWrHVLqDIKz9q4IrAvltVsW8bYLq+pAR/+a10igD+rlr2rG2QKl4 icCT4/rzUj+PWUl0TusZ8Y+vG+htsYE1M4w8eCLQf/lHAVSPDVn/T59HYRkoORAem5yaLdtR/k55B qPUsIgJQNcetjr3Zm8Om3Jjl9DnzhqSLuID+1sBCtu0DZgWmP+utREU2vjESN5mVNkiJjhS1PUrBL VVVLHuaAG5fYNm1B4W8YV8mXlr725gW4Y43QDhlswrnYPOtNHO+uB7HEDovXC2KWgZkVKq1iQAKkA 4qEg9BLw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vGH00-0000000BsYV-2ka9; Tue, 04 Nov 2025 13:23:00 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vGGzy-0000000BsXb-1q9x for linux-arm-kernel@lists.infradead.org; Tue, 04 Nov 2025 13:22:59 +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 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 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251104_052258_616249_EFFE9DB1 X-CRM114-Status: GOOD ( 19.86 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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