From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1851A1E89C; Tue, 27 May 2025 17:16:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748366217; cv=none; b=hbEoBjcLo9aDXbDLcSZlTEan+itMhIepNABkVwVT7iRwegSZtEH7sb3j9OTtYfm3A1qjjA0wU6lEn0+eVhExtL9Ex6Gq3n+NkdZKv9wXZfKSIrNKiFxbyVy47xMGoNR8gAC+a1feGgxnTwHtcmfjZSqqIKu6hu5GkozVa+/+fW0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748366217; c=relaxed/simple; bh=Yqy9Uyvkm9+zumNQdiPHR16Cdosd92f+Lgj504gOn5o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=P8wlgzVNpZvsLzif8pEwaxawhm69E/L++3h9b9J9OBtsFeuSsK7lrjsTUSQgvgNkOdcLLJKRXMmJmwG9ZqZuqBWCniTJGArRr0oob3KwsekN8vll1XOxPLkv2epdDKWJvbmo72UgZs71kc+xovSxLb++2Mg3ZBiAy/L5JKEVUMc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=jVdl/ZII; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="jVdl/ZII" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B155C4CEE9; Tue, 27 May 2025 17:16:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1748366217; bh=Yqy9Uyvkm9+zumNQdiPHR16Cdosd92f+Lgj504gOn5o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jVdl/ZIIzGRt/6Emm9XBI+PWeCEtVvdVvqf3IqMc58DhKoHaaHTSkZ/nmuRfGPTUl Kl2oJbfPdFwKb1EZCAG30+jQhangCeG0TM8V9ftl4JZH89UaEfUSKbwe/ZLLot1Oqs 4/kcTAlVDKVrRoY6yA5tFq9+72HQQ4UBC8hkTChc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Bert Karwatzki , Balbir Singh , Ingo Molnar , Brian Gerst , Juergen Gross , "H. Peter Anvin" , Linus Torvalds , Andrew Morton , Christoph Hellwig , Pierre-Eric Pelloux-Prayer , Alex Deucher , =?UTF-8?q?Christian=20K=C3=B6nig?= , David Airlie , Simona Vetter Subject: [PATCH 6.12 625/626] x86/mm/init: Handle the special case of device private pages in add_pages(), to not increase max_pfn and trigger dma_addressing_limited() bounce buffers bounce buffers Date: Tue, 27 May 2025 18:28:38 +0200 Message-ID: <20250527162510.396791895@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250527162445.028718347@linuxfoundation.org> References: <20250527162445.028718347@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Balbir Singh commit 7170130e4c72ce0caa0cb42a1627c635cc262821 upstream. As Bert Karwatzki reported, the following recent commit causes a performance regression on AMD iGPU and dGPU systems: 7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems") It exposed a bug with nokaslr and zone device interaction. The root cause of the bug is that, the GPU driver registers a zone device private memory region. When KASLR is disabled or the above commit is applied, the direct_map_physmem_end is set to much higher than 10 TiB typically to the 64TiB address. When zone device private memory is added to the system via add_pages(), it bumps up the max_pfn to the same value. This causes dma_addressing_limited() to return true, since the device cannot address memory all the way up to max_pfn. This caused a regression for games played on the iGPU, as it resulted in the DMA32 zone being used for GPU allocations. Fix this by not bumping up max_pfn on x86 systems, when pgmap is passed into add_pages(). The presence of pgmap is used to determine if device private memory is being added via add_pages(). More details: devm_request_mem_region() and request_free_mem_region() request for device private memory. iomem_resource is passed as the base resource with start and end parameters. iomem_resource's end depends on several factors, including the platform and virtualization. On x86 for example on bare metal, this value is set to boot_cpu_data.x86_phys_bits. boot_cpu_data.x86_phys_bits can change depending on support for MKTME. By default it is set to the same as log2(direct_map_physmem_end) which is 46 to 52 bits depending on the number of levels in the page table. The allocation routines used iomem_resource's end and direct_map_physmem_end to figure out where to allocate the region. [ arch/powerpc is also impacted by this problem, but this patch does not fix the issue for PowerPC. ] Testing: 1. Tested on a virtual machine with test_hmm for zone device inseration 2. A previous version of this patch was tested by Bert, please see: https://lore.kernel.org/lkml/d87680bab997fdc9fb4e638983132af235d9a03a.camel@web.de/ [ mingo: Clarified the comments and the changelog. ] Reported-by: Bert Karwatzki Tested-by: Bert Karwatzki Fixes: 7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems") Signed-off-by: Balbir Singh Signed-off-by: Ingo Molnar Cc: Brian Gerst Cc: Juergen Gross Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Andrew Morton Cc: Christoph Hellwig Cc: Pierre-Eric Pelloux-Prayer Cc: Alex Deucher Cc: Christian König Cc: David Airlie Cc: Simona Vetter Link: https://lore.kernel.org/r/20250401000752.249348-1-balbirs@nvidia.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/mm/init_64.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -967,9 +967,18 @@ int add_pages(int nid, unsigned long sta ret = __add_pages(nid, start_pfn, nr_pages, params); WARN_ON_ONCE(ret); - /* update max_pfn, max_low_pfn and high_memory */ - update_end_of_memory_vars(start_pfn << PAGE_SHIFT, - nr_pages << PAGE_SHIFT); + /* + * Special case: add_pages() is called by memremap_pages() for adding device + * private pages. Do not bump up max_pfn in the device private path, + * because max_pfn changes affect dma_addressing_limited(). + * + * dma_addressing_limited() returning true when max_pfn is the device's + * addressable memory can force device drivers to use bounce buffers + * and impact their performance negatively: + */ + if (!params->pgmap) + /* update max_pfn, max_low_pfn and high_memory */ + update_end_of_memory_vars(start_pfn << PAGE_SHIFT, nr_pages << PAGE_SHIFT); return ret; }