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 6B37A330B20 for ; Fri, 17 Oct 2025 15:50:18 +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=1760716220; cv=none; b=djumVi0aI2tSghLomzKNZUYcUjsAT5O4H6834LGttElaOfpS21bptAWJUK6HnBnGiVl6vSaFDWNfUC+3qOzX4Gzg4UNWBgbQch6u0mvKS9ROMD2FECUz/XD0vM35EM0/j3Mj+bu1LrciH8qPF8Ra0S+rpLq4dlniVxk61U1ZOBw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760716220; c=relaxed/simple; bh=wWWU0Gyd+dk7dAb3argi3LBrZh2fIuZUjix4Eb0LtYU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XApT5+uqW5lLt1wi4BzMDq3Xi0ld2GuT3JAnao2lnEy4IUu6Pl9hQYjvS6QX9fWdSFqJk/VM5Oq86X5/gLbu1Tqu5un4Zjq+bEa+SvCD/GjkemPejI1cx4Uz56kfSrl9r8okddxdcKUih0PifkWrv2IUibYFFc+4meMdhkEXz28= 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 722161595; Fri, 17 Oct 2025 08:50:09 -0700 (PDT) Received: from [10.163.68.204] (unknown [10.163.68.204]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A5A7C3F66E; Fri, 17 Oct 2025 08:50:14 -0700 (PDT) Message-ID: Date: Fri, 17 Oct 2025 21:20:10 +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 2/2] arm64: mm: relax VM_ALLOW_HUGE_VMAP if BBML2_NOABORT is supported To: Yang Shi , ryan.roberts@arm.com, cl@gentwo.org, catalin.marinas@arm.com, will@kernel.org Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20251013232803.3065100-1-yang@os.amperecomputing.com> <20251013232803.3065100-3-yang@os.amperecomputing.com> <05331884-9723-48ff-a3ce-c2ea023bbabd@os.amperecomputing.com> Content-Language: en-US From: Dev Jain In-Reply-To: <05331884-9723-48ff-a3ce-c2ea023bbabd@os.amperecomputing.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 17/10/25 12:20 am, Yang Shi wrote: > > > On 10/14/25 11:50 PM, Dev Jain wrote: >> >> On 14/10/25 4:57 am, Yang Shi wrote: >>> When changing permissions for vmalloc area, VM_ALLOW_HUGE_VMAP area is >>> exclueded because kernel can't split the va mapping if it is called on >>> partial range. >>> It is no longer true if the machines support BBML2_NOABORT after commit >>> a166563e7ec3 ("arm64: mm: support large block mapping when >>> rodata=full"). >>> So we can relax this restriction and update the comments accordingly. >>> >>> Fixes: a166563e7ec3 ("arm64: mm: support large block mapping when >>> rodata=full") >>> Signed-off-by: Yang Shi >>> --- >>>   arch/arm64/mm/pageattr.c | 13 +++++++------ >>>   1 file changed, 7 insertions(+), 6 deletions(-) >>> >>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c >>> index c21a2c319028..b4dcae6273a8 100644 >>> --- a/arch/arm64/mm/pageattr.c >>> +++ b/arch/arm64/mm/pageattr.c >>> @@ -157,13 +157,13 @@ static int change_memory_common(unsigned long >>> addr, int numpages, >>>         /* >>>        * Kernel VA mappings are always live, and splitting live section >>> -     * mappings into page mappings may cause TLB conflicts. This means >>> -     * we have to ensure that changing the permission bits of the >>> range >>> -     * we are operating on does not result in such splitting. >>> +     * mappings into page mappings may cause TLB conflicts on the >>> machines >>> +     * which don't support BBML2_NOABORT. >>>        * >>>        * Let's restrict ourselves to mappings created by vmalloc (or >>> vmap). >>> -     * Disallow VM_ALLOW_HUGE_VMAP mappings to guarantee that only >>> page >>> -     * mappings are updated and splitting is never needed. >>> +     * Disallow VM_ALLOW_HUGE_VMAP mappings if the systems don't >>> support >>> +     * BBML2_NOABORT to guarantee that only page mappings are >>> updated and >>> +     * splitting is never needed on those machines. >>>        * >>>        * So check whether the [addr, addr + size) interval is entirely >>>        * covered by precisely one VM area that has the VM_ALLOC flag >>> set. >>> @@ -171,7 +171,8 @@ static int change_memory_common(unsigned long >>> addr, int numpages, >>>       area = find_vm_area((void *)addr); >>>       if (!area || >>>           end > (unsigned long)kasan_reset_tag(area->addr) + >>> area->size || >>> -        ((area->flags & (VM_ALLOC | VM_ALLOW_HUGE_VMAP)) != VM_ALLOC)) >>> +        !(area->flags & VM_ALLOC) || ((area->flags & >>> VM_ALLOW_HUGE_VMAP) && >>> +        !system_supports_bbml2_noabort())) >>>           return -EINVAL; >>>         if (!numpages) >> >> This will conflict with my upcoming vmalloc-huge series, so best to >> leave it to me, >> I already have this included :) > > My point is that I hope this can be merged as a hotfix for 6.18. I > have no strong opinion on either the maintainers take this one or from > your series. But if this will go into 6.18 as a hotfix, it should be > also a prerequisite patch (standalone)  in your series, and the rest > of your series should be based on top of it. Of course this argument > will not stand if we don't care to have it fixed for 6.18. I see what you mean, but I don't think this patch should be treated as a hotfix. We forgot to relax a restriction - that's fine. That is not an incorrectness in the linear map series. A fix usually fixes an incorrectness. > > Thanks, > Yang > >