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 2C485C9830E for ; Thu, 24 Sep 2026 17:06:42 +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:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=9TixM1+IUrYtSdrp0PZoLfQTpUcfWhPbpy3zROHng5c=; b=jmIeVVoNHskjF0GBM59en6S/DK wY1uSkM//Fh75nZtIHhYfpF/bNRgRc+7xuIO9wtnEjZMiAtYuR85d2mX+hG3fnAXtM9Kol8tg9IIH lRub/IA9eYxZtLiZLOOPPDCcL7FTOzQ/bX5ANP5zYY6F/Rg/z5Xcbw60ua5ZeR34/Vy+9b7NLBjtn bzOdrXL4ZYDQFpJbBIdqtvTJzyxDPEnD6eugl63XmP3ZFVA1JV8EoWI2D/f8ZLo/0IST1OudKkU83 7LvlY6KFGUq0QYliFikwLUmc0B+v9KXJGe6L7Jnrchj6s9j+Lq0Wvi6JRo+fnTdH6GVvvtMBuEJjG +hnTS94Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x9mu3-0000000BgmO-1ceP; Thu, 24 Sep 2026 17:06:35 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x9mu1-0000000Bgm1-1BPJ for linux-arm-kernel@lists.infradead.org; Thu, 24 Sep 2026 17:06:33 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 5D1EF601DE; Thu, 24 Sep 2026 17:06:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 305E71F000FF; Thu, 24 Sep 2026 17:06:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790269592; bh=9TixM1+IUrYtSdrp0PZoLfQTpUcfWhPbpy3zROHng5c=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=btBZn0S9HCNXjZe78EQsL/onpDdftjtBgAhc7zkF9MAd7ZxdIvXKc52S7kB3QRR2r whw0vvQkjE+AGmj39xNkQyG9q4EI3f2yGyJWCLID36R0LijAmvVKr/Xf1IfJOhKHFm SG+c6PT6vnS4xhtWi2qvmm8B+PUlMOu9OF5BkpsLhhH5Vi5RiR6c3ztfZtKihJCCsm t1JeQfD4QZgbUCcCB2XZKsJdpTgJD+s0RQ8Yc0bpWl1q+In26PWBQeIFpnk4UZwBmF /Xfg0Y6QiO7CQqsUE0jzOE+S2ENZv+Uzsg3NGUuDEu04o7EMetVMsb9szct3iZDnow CNoW6ITZHfoPw== Date: Thu, 24 Sep 2026 20:06:26 +0300 From: Mike Rapoport To: Ard Biesheuvel Cc: Vladimir Murzin , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , liulhong617 Subject: Re: [PATCH] arm64: mm: Fix pfn_is_map_memory() misreporting mapped memory Message-ID: References: <20260908162033.74509-1-vladimir.murzin@arm.com> <947a1506-dfe4-4906-9673-6a7227946433@app.fastmail.com> <01f1f6d9-e10f-43f9-b731-f6393010a11c@app.fastmail.com> <7a6793e4-b2ef-46e0-a068-9166d3f10ea3@app.fastmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7a6793e4-b2ef-46e0-a068-9166d3f10ea3@app.fastmail.com> 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 Thu, Sep 24, 2026 at 12:59:15PM +0200, Ard Biesheuvel wrote: > On Tue, 22 Sep 2026, at 07:50, Mike Rapoport wrote: > > On Thu, Sep 17, 2026 at 05:17:45PM +0200, Ard Biesheuvel wrote: > >> On Thu, 17 Sep 2026, at 16:29, Mike Rapoport wrote: > >> > On Thu, Sep 17, 2026 at 02:34:57PM +0200, Ard Biesheuvel wrote: > >> >> > >> >> > >> >> On Thu, 17 Sep 2026, at 14:26, Vladimir Murzin wrote: > >> >> > On 9/16/26 11:13, Ard Biesheuvel wrote: > >> >> >> (cc Mike) > >> >> >> > >> >> >> On Tue, 8 Sep 2026, at 18:20, Vladimir Murzin wrote: > >> >> >>> Commit 7ace06a01efa ("arm64: mm: fix accidental linear mapping of > >> >> >>> no-map reserved memory") removed sub-page no-map regions from the > >> >> >>> linear mapping. However, pfn_is_map_memory() can still report that > >> >> >>> such a region is mapped. > >> >> >>> > >> >> >>> For instance, with 64K pages, say we have > >> >> >>> > >> >> >>> normal: ...–0xa2007fff > >> >> >>> no-map: 0xa2008000–0xa200ffff > >> >> >>> normal: 0xa2010000–... > >> >> >>> > >> >> >>> The range 0xa2000000–0xa200ffff is not linearly mapped, but > >> >> >>> pfn_is_map_memory(__phys_to_pfn(0xa2008000)) aligns the address to > >> >> >>> page granularity and passes 0xa2000000 to memblock_is_map_memory(). > >> >> >>> That address belongs to the preceding normal memblock region, so the > >> >> >>> no-map region is ignored and the function returns true. > >> >> >>> > >> >> >>> Fix that by checking if entire page is subset of memory block. > >> >> >>> > >> >> >>> Fixes: 7ace06a01efa ("arm64: mm: fix accidental linear mapping of > >> >> >>> no-map reserved memory") > >> >> >>> Assisted-by: LLM > >> >> >>> Signed-off-by: Vladimir Murzin > >> >> >>> --- > >> >> >>> arch/arm64/mm/init.c | 3 ++- > >> >> >>> 1 file changed, 2 insertions(+), 1 deletion(-) > >> >> >>> > >> >> >>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > >> >> >>> index fbf215ecc7d0..5da80e1e1727 100644 > >> >> >>> --- a/arch/arm64/mm/init.c > >> >> >>> +++ b/arch/arm64/mm/init.c > >> >> >>> @@ -172,7 +172,8 @@ int pfn_is_map_memory(unsigned long pfn) > >> >> >>> if (PHYS_PFN(addr) != pfn) > >> >> >>> return 0; > >> >> >>> > >> >> >>> - return memblock_is_map_memory(addr); > >> >> >>> + return memblock_is_region_memory(addr, PAGE_SIZE) && > >> >> >>> + memblock_is_map_memory(addr); > >> >> >>> } > >> >> >>> EXPORT_SYMBOL(pfn_is_map_memory); > >> >> >>> > >> >> >> memblock_is_region_memory() only tells you whether the range in > >> >> >> question is covered by a single entry in memblock.memory.regions[]. > >> >> >> > >> >> >> memblock has other flags, which may or may not be set on sub-page > >> >> >> regions too. So I don't think this is the right solution in the > >> >> >> general case, even if it fixes your example. > >> >> >> > >> >> > > >> >> > Ack. > >> >> > > >> >> >> Given that the no-map attribute fundamentally only applies to page > >> >> >> granular regions, it would make sense to round those outwards > >> >> >> whenever they are created. > >> >> >> > >> >> >> --- a/mm/memblock.c > >> >> >> +++ b/mm/memblock.c > >> >> >> @@ -1119,6 +1119,10 @@ > >> >> >> int __init_memblock memblock_mark_nomap(phys_addr_t base, phys_addr_t size) > >> >> >> { > >> >> >> + phys_addr_t end = PAGE_ALIGN(base + size); > >> >> >> + > >> >> >> + base &= PAGE_MASK; > >> >> >> + size = end - base; > >> >> >> return memblock_setclr_flag(&memblock.memory, base, size, 1, MEMBLOCK_NOMAP); > >> >> >> } > >> >> >> > >> >> >> > >> >> > > >> >> > Should the same be applied to memblock_clear_nomap()? > >> >> > > >> >> > >> >> Yes. > >> >> > >> >> > This is indeed much nicer way to fix the problem! Now, when no-map is > >> >> > rounded outwards, do we still need 7ace06a01efa? > >> >> > > >> >> > >> >> Probably not, but there are some corner cases to consider before we > >> >> go down this route: > >> >> - what happens when marking a range no-map where the outward rounding > >> >> would exceed the limits of the existing memblock memory range? > >> >> - what happens when removing a non-page aligned region from memblock > >> >> that intersects with a (page aligned) no-map region? > >> > > >> > Another thing is that maybe we should force memblock.memory only to page > >> > aligned ranges. x86 uses memblock_trim_memory() for that since, like, > >> > forever. > >> > > >> > >> Interesting. It would make sense to do the same on arm64. > >> > >> But if a NOMAP region ends in the middle of a page, that code will trim on > >> both sides, and throw away the shared page entirely. > > > > Honestly, I think the whole sub-page NOMAP is firmware's problem. > > Not entirely. The firmware does not know whether the OS will use 4k pages > or 64k pages, and rounding up all reservations to 64k just in case might > be wasteful. I keep forgetting about 64k pages :) > So I think it is reasonable to require 4k alignment for NOMAP regions, > and the OS should decide whether to round outward or not. It does mean > that the firmware should avoid treating the misaligned pieces at the > edges as memory where it can place things like initrd etc. > > > While > > rounding up in _mark_nomap() makes sense because we cannot "not map" a > > sub-page range, I would add a big fat WARN_ON("FIX YOUR FIRMWARE") if the > > rounding actually happens. > > > > I don't think that is very productive for 4k -> 64k rounding. I agree that the strict requirement should be for 4k. Or without loss of generality "minimal supported base page size" :) > > As for the trimming on arm64, I believe that's relevant, because again, we > > cannot really work with sub-page ranges in memblock.memory and they are > > anyway discarded by for_each_mem_pfn_range() that's used all over mm > > initialization. > > > > Yeah I think the rounding is needed in any case, but I don't think it is > the firmware's job to mark unrelated adjacent memory as no-map only because > the OS might decide to use a coarser granule. I afraid this will create weird edge cases where firmware mixes parts of a 64k pages for no-map and other things at 4k granularity. -- Sincerely yours, Mike.