From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3DAF637C0F7 for ; Mon, 8 Jun 2026 12:43:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780922639; cv=none; b=m04HmNlPmYf5t9Em7OTxZPwxrmI7/UG2ya06PGM5gveWe5Y4/wFLFFwvi1cPriwNt/M5RGrc8z1pypHloKKcduc2MyGUcgSgc3fnFuS+v9Ecnf/iqjxgz+Ru2Dq15gzVB6Hqyh2O/7xjtkalcWnHIm3ELHKReETk2hi//4WLW8Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780922639; c=relaxed/simple; bh=/gToq6YVE1uIZ4c2/SMMkiRTrGl6wf6v7ynCmQ2aI5I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Mo2Q9a+q1PWD3NR1jo954ef5wHc3TBZOYRhpu9vvVeE7+9njjTi/Ix64HspTLm3J049RNgrHt608KJiEltp708J07d2ocKMsUVfGtytH+MBIRfAYcpZuBZmCGWatuIu7bWYREvyhHJHkXIyMcYjNEOzlyz261swVEPIthaIdr2A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DHnK39Pr; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DHnK39Pr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B54371F00893; Mon, 8 Jun 2026 12:43:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780922637; bh=jLcAgrGvi7SdC6jzoWYkO8ugj2qnlkxJAEGttFGnMYI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=DHnK39PrKhgM7DYyE01pxLC54LX0SCxyFWnIQzirig+X6sZr2BHTLJf6S2tHfhKvL eO7n9PDRIir2s2KuMp6sM0ondR+wUlGC+jLXoElgEEzFubTr5tpX/U4heFDIpvBgdT WBqn+pZeyDxEtzZbSbJclOQ+p9AMnn2KM6RdmMVnMoOqVQYFNgIZgf6RtNnDKDRunW um9mx6AV8C82N/6ZLatVW2MQJL0kdSA/nKNyVtED30vgmaIuhzBgVs/DA1e2ex6uMl xtYvnMRJXGNhVz9BbXsztfLcfTX88DXUXhfGU+wv/5v3mQtX58GiiqB42UVneQ2Tqf MSh7xYhvgNZAQ== Message-ID: <3c88dee8-6fcd-4f72-9a73-17044214b087@kernel.org> Date: Mon, 8 Jun 2026 14:43:52 +0200 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 v3] riscv: mm: Avoid spurious fault after hotplugging vmemmap To: Vivian Wang , Paul Walmsley , Palmer Dabbelt , Alexandre Ghiti , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260605-mark-after-vmemmap-populate-v3-1-a06001ac9264@iscas.ac.cn> <953d7a60-456d-4629-b133-afce62cc5b3e@iscas.ac.cn> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <953d7a60-456d-4629-b133-afce62cc5b3e@iscas.ac.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/8/26 04:24, Vivian Wang wrote: > On 6/5/26 17:16, David Hildenbrand (Arm) wrote: >> On 6/5/26 07:23, Vivian Wang wrote: >>> section_activate() does not flush TLB after populating new vmemmap >>> pages. On most architectures, this is okay. However it is a problem on >>> RISC-V since there the TLB caching non-present entries is permitted, >>> which causes spurious faults on some hardwares. >>> >>> This seems to be most easily reproduced with DEBUG_VM=y and >>> PAGE_POISONING=y, which causes these newly mapped struct pages to be >>> poisoned i.e. written to immediately after mapping. >>> >>> Add a hook vmemmap_populate_finalize() in __populate_section_memmap() >>> after population, to allow architectures to handle such situations as >>> needed. Then implement it on RISC-V to arrange for the existing >>> exception handler code to deal with these faults if they happen. >>> >>> Signed-off-by: Vivian Wang >>> --- >>> Depends on my earlier kfence fixes for mark_new_valid_map() [1]. >>> >>> Found while testing AMD_HSA/ZONE_DEVICE on SpacemiT K3. Using >>> ZONE_DEVICE requires another fix [2]. >>> >>> [1]: https://lore.kernel.org/linux-riscv/20260303-handle-kfence-protect-spurious-fault-v2-0-f80d8354d79d@iscas.ac.cn >>> [2]: https://lore.kernel.org/linux-riscv/20260309-riscv-sparsemem-vmemmap-limits-v1-2-f40efe18e3cd@iscas.ac.cn >>> --- >>> Changes in v3: >>> - Merged back into one patch (Mike) >>> - (No code changes otherwise.) >>> - Link to v2: https://patch.msgid.link/20260604-mark-after-vmemmap-populate-v2-0-ab6a7d03b434@iscas.ac.cn >>> >>> Changes in v2: >>> - Split patch in two, hook point and riscv hook >>> - Explain hook necessity in patch 1 message (Mike) >>> - Make hook #define based (Mike) >>> - Call finalize hook only on populate success >>> - Link to v1: https://patch.msgid.link/20260525-mark-after-vmemmap-populate-v1-1-e698d859ba16@iscas.ac.cn >>> --- >>> arch/riscv/include/asm/pgtable.h | 4 ++++ >>> arch/riscv/mm/init.c | 6 ++++++ >>> mm/sparse-vmemmap.c | 8 ++++++++ >>> 3 files changed, 18 insertions(+) >>> >>> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h >>> index a1a7c6520a09..aa0f50e3d534 100644 >>> --- a/arch/riscv/include/asm/pgtable.h >>> +++ b/arch/riscv/include/asm/pgtable.h >>> @@ -1243,6 +1243,10 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte) >>> #define TASK_SIZE FIXADDR_START >>> #endif >>> >>> +/* Needed on SPARSEMEM_VMEMMAP */ >>> +#define vmemmap_populate_finalize vmemmap_populate_finalize >>> +void __meminit vmemmap_populate_finalize(void); >>> + >>> #else /* CONFIG_MMU */ >>> >>> #define PAGE_SHARED __pgprot(0) >>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c >>> index 706f43523935..cf9ae4099f82 100644 >>> --- a/arch/riscv/mm/init.c >>> +++ b/arch/riscv/mm/init.c >>> @@ -1360,6 +1360,12 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, >>> */ >>> return vmemmap_populate_hugepages(start, end, node, altmap); >>> } >>> + >>> +void __meminit vmemmap_populate_finalize(void) >>> +{ >>> + /* Avoid faults on cached non-present TLB entries. */ >>> + mark_new_valid_map(); >>> +} >>> #endif >> How does mark_new_valid_map() handle concurrent access? >> >> There is some comment in there, but I am not sure if that actually implies that >> mark_new_valid_map() can be called concurrently from arbitrary context? > > AFAICT, yes, it is intended to be used concurrently from arbitrary > context, and this is why I used them. > > I had not originally written the code, so some riscv maintainer can > maybe chime in on this, but as I understand it the idea is that we only > ever set bits in the bitmap in mark_new_valid_map() while "allocating", > whereas the assembly code in handle_exception in > arch/riscv/kernel/entry.S only ever clears individual bits. So at least > the access to the bitmap itself should be fine. Right, flush_cache_vmap() looks like a bitmap_set() -- non-atomically. .Lnew_vmalloc_kernel_address does an atomic bitmap clearing ("Atomically reset the current cpu bit in new_vmalloc"). I am primarily wondering whether we'd want atomic bit-setting as well? > > This was added in commit 503638e0babf ("riscv: Stop emitting preventive > sfence.vma for new vmalloc mappings"). > > Do you think the mark_new_valid_map() function needs extra > synchronization like smp_wmb()? Right, I wonder about atomic access, but also about memory barriers. -- Cheers, David