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 E08E9C982D2 for ; Fri, 18 Sep 2026 06:05:51 +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=2iSN1j31Sw9qmqTYVp6Ry3mKQfg4lt3sT+FCrOQ8mF4=; b=xtsznH5RKATxpNWF/uQtF1/bO1 2fnQe+9YMEEhLUuaseGLcR5oPcrsCCZR5VdBaErj9u26BumHz1AnZq3DCNKWrX87XEf9u7Rs6K0/p nRsobe3GM4Of7mJruXQAPaYkEj/Aojuvn+bzIY2R06dltjsvny6ndgY4gD2qam2e1flZ1wYd5oZXC xYXPf8FqJIkXfr56I7zp6QLWyjffw0wj2GCtphAhbmGCym7rwaurctIUvwO6/5NygtPFXkDc4t1fY lu9iv2UQRdWEjf/Dt1gDq6nNWSQfTC6m0Sktq1jVoj8D+WWE3ahiHoxISLaL7FzjR6JNVwxPc5UK6 HbnXQhTA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x7RjE-0000000DWuH-2GNL; Fri, 18 Sep 2026 06:05:44 +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 1x7RjD-0000000DWuB-3lYk for linux-arm-kernel@lists.infradead.org; Fri, 18 Sep 2026 06:05:44 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id B76F8601EF; Fri, 18 Sep 2026 06:05:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2DB971F000FF; Fri, 18 Sep 2026 06:05:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789711542; bh=2iSN1j31Sw9qmqTYVp6Ry3mKQfg4lt3sT+FCrOQ8mF4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HRYJtWuL74SbBnfcEwdWnfbXL/tQ2LS0eZcRDZCBlNLQXBydIBtYqkiENXlDagnbT C2yEEFg2K7h5z+2opnb1JHsi/x+l+mdBVTLNqkvv/DpshLB82Svt8wnmGViSmp38iu RqWJqCe9NjqFd7sIoVai7vkuR1L3g/ELqekIScdjqxdSM+2tF1sE2M5vUb+ybXhH2T qeHd1/7ezHu35c25/Re5wk4kWvG7SMvYr71yv/QjO7HFaVvMkPqGp28tk2Tjav58QQ 8Q3/O3ocmaqrfak5BYTC5KAwevQhgl+fUqMCEBp14MV+FG3sEjD8+8xfzUSXElZXjR UltrRtZcQGVSg== Message-ID: <2462f67c-f7d3-4eb3-a093-6a338ef49f14@kernel.org> Date: Fri, 18 Sep 2026 08:05:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 03/10] mm/vmalloc: use pte_set_huge()/pte_clear_huge() for PTE-level block mappings To: Barry Song , Wen Jiang Cc: akpm@linux-foundation.org, catalin.marinas@arm.com, linux-mm@kvack.org, urezki@gmail.com, will@kernel.org, Xueyuan.chen21@gmail.com, ajd@linux.ibm.com, anshuman.khandual@arm.com, david@kernel.org, dev.jain@arm.com, jiangwen6@xiaomi.com, leo.yan@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, rppt@kernel.org, ryan.roberts@arm.com References: <20260917052933.188679-1-jiangwenxiaomi@gmail.com> <20260917052933.188679-4-jiangwenxiaomi@gmail.com> <27072d94-13bf-4bea-948a-d8a67976601e@kernel.org> Content-Language: fr-FR From: "Christophe Leroy (CS GROUP)" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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 Le 17/09/2026 à 23:44, Barry Song a écrit : > On Thu, Sep 17, 2026 at 10:41 PM Wen Jiang wrote: >> >> On Thu, 17 Sept 2026 at 22:00, Christophe Leroy (CS GROUP) >> wrote: >>> >>> >>> >>> Le 17/09/2026 à 07:29, Wen Jiang a écrit : >>>> From: Wen Jiang >>>> >>>> vmap installs PTE-level block mappings by reusing set_huge_pte_at() and >>>> huge_ptep_get_and_clear() under #ifdef CONFIG_HUGETLB_PAGE. This makes >>>> the feature silently unavailable on CONFIG_HUGETLB_PAGE=n kernels and >>>> couples mm/vmalloc.c to HugeTLB internals it does not otherwise need. >>>> >>>> Now that arm64 and powerpc/8xx provide pte_set_huge() and >>>> pte_clear_huge(), add the generic fallbacks next to the existing >>>> pmd/pud_set_huge() family and convert vmap_pte_range() and >>>> vunmap_pte_range() to the new helpers. The CONFIG_HUGETLB_PAGE guards >>>> around the block-mapping paths are dropped, so PTE-level block mappings >>>> now also work on CONFIG_HUGETLB_PAGE=n kernels, and mm/vmalloc.c no >>>> longer includes . >>>> >>>> The fallbacks exist only to keep the build working on architectures >>>> without PTE-level block mapping support. They are unreachable there: >>>> the callers only run when arch_vmap_pte_range_map_size() or >>>> arch_vmap_pte_range_unmap_size() return a size other than PAGE_SIZE, >>>> which requires an arch implementation. WARN_ON_ONCE() makes that >>>> explicit rather than silently doing nothing. >>>> >>>> Signed-off-by: Wen Jiang >>>> --- >>>> include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++ >>>> mm/vmalloc.c | 19 ++++++------------- >>>> 2 files changed, 35 insertions(+), 13 deletions(-) >>>> >>>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >>>> index cdd68ed3ae1a9..349ced999f959 100644 >>>> --- a/include/linux/pgtable.h >>>> +++ b/include/linux/pgtable.h >>>> @@ -2134,6 +2134,35 @@ static inline int pmd_free_pte_page(pmd_t *pmd, unsigned long addr) >>>> } >>>> #endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */ >>>> >>>> +/* >>>> + * PTE-level block mappings for vmap. >>>> + * >>>> + * pte_set_huge() only has to be implemented by architectures whose >>>> + * arch_vmap_pte_range_map_size() can return a size other than PAGE_SIZE. >>>> + */ >>>> +#ifndef __HAVE_ARCH_PTE_SET_HUGE >>>> +static inline void pte_set_huge(pte_t *ptep, unsigned long addr, >>>> + phys_addr_t phys, pgprot_t prot, >>>> + unsigned long size) >>>> +{ >>>> + WARN_ON_ONCE(1); >>> >>> BUILD_BUG_ON() would be better here. >>> >>> It should be possible because fallback arch_vmap_pte_range_map_size() >>> will constant-fold PAGE_SIZE so pte_set_huge() will never be called. >>> >> >> Agreed. These fallbacks exist only to keep the build working on >> architectures with PTE-level block mappings and should never actually >> be reached, so BUILD_BUG_ON() is right. I'll make that change in v9. >> > > I am not quite sure. It won't be called at runtime because > `vmap size`/`unmap size` return `PAGE_SIZE`, so the code won't > reach this branch. But it will still be built. The fallbacks are defined as: #ifndef arch_vmap_pte_range_map_size static inline unsigned long arch_vmap_pte_range_map_size(unsigned long addr, unsigned long end, u64 pfn, unsigned int max_page_shift) { return PAGE_SIZE; } #endif #ifndef arch_vmap_pte_range_unmap_size static inline unsigned long arch_vmap_pte_range_unmap_size(unsigned long addr, pte_t *ptep) { return PAGE_SIZE; } #endif Therefore in: size = arch_vmap_pte_range_unmap_size(addr, pte); if (size != PAGE_SIZE) { GCC knows 'size' is const and its value is PAGE_SIZE, so it won't emit the branch at all. It is call constant folding, some explanation here: https://en.wikipedia.org/wiki/Constant_folding > > So, would a `BUILD_BUG_ON()` trigger a build failure here? It shouldn't, if it does it is a compiled bug or this is because someone has redefined arch_vmap_pte_range_map_size() and not pte_set_huge() which we'd better know at build time rather than at runtime. > > Best Regards > Barry >