From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (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 2203C165F13; Thu, 16 Oct 2025 11:17:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760613433; cv=none; b=JhT2K2wZk2KcpR2W+cdwAwppZmHkhGKt2xDTbCAj0jQhTGSh9TIWOKZ6TzK/vNjmvL7LSTREd3Idk9m3JmBjN4x9K2HHBwOfjgcFAZ3JYeFiZkslpOEZWaucSo+QaWCyAODj0T5GqWUbXKBFfMP3ZpvrB6t9M+vvZEc/QT4JlKs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760613433; c=relaxed/simple; bh=DSWwjOXOC7bi7nAeIFr1fihi8RD0f4mgzm3t1e4srsw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Cs68DFeuRw8I3rbY1HKJQ+6/6fTBsk+lp6IYbxsKi/qVTI20RYYLySKFCv36M3oepC9eK/aXnS44gGNsLcf68lgu2SWCNDteky3ZFOdWsO5A6qji6swDu6xEvX34K3plyt0llh9y53av/OPPigY1QfPkKXjWczCIvpy8myVY7xg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=hxewQKBU; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="hxewQKBU" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1760613429; bh=DSWwjOXOC7bi7nAeIFr1fihi8RD0f4mgzm3t1e4srsw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=hxewQKBU4XBHVdn3n/KWzRglcS5kWQfTmJoEpRWVU198WIarQ/E/+omVH/nlKQX86 zAeUuogdHv/xjZLpNQ5nYCedzd5JkS8lINjMIOZ+2UbMzQLQO2ie1ZhE/JJ8+rSr1t gU6UQhHE0FeXHYklZgaWiD7c4UI1m1YLcHSrqe/gcID9ypINTXCRdjOjrQU9APyPJh IQ7djMFdCLeplC77JE9a1JNCPjJPBYOGMzeQ7JOk2pHwdEnPDqf8t9CWC5Mm6/lqIk +WSWiXPyBreEMGKgPGQZPAEGB887tu0Is9V//WxznJuFGUUVk/Z5bfYL3y1/LCK1en jE954CUpZbWmQ== Received: from [IPV6:2a01:e0a:5e3:6100:7aed:fe0e:8590:cbaa] (unknown [IPv6:2a01:e0a:5e3:6100:7aed:fe0e:8590:cbaa]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: loicmolinari) by bali.collaboradmins.com (Postfix) with ESMTPSA id 0F59C17E0C54; Thu, 16 Oct 2025 13:17:08 +0200 (CEST) Message-ID: Date: Thu, 16 Oct 2025 13:17:07 +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 v4 03/13] drm/shmem-helper: Map huge pages in fault handlers To: Matthew Wilcox Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Boris Brezillon , Rob Herring , Steven Price , Liviu Dudau , Melissa Wen , =?UTF-8?Q?Ma=C3=ADra_Canal?= , Hugh Dickins , Baolin Wang , Andrew Morton , Al Viro , =?UTF-8?Q?Miko=C5=82aj_Wasiak?= , Christian Brauner , Nitin Gote , Andi Shyti , Jonathan Corbet , Christopher Healy , Bagas Sanjaya , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, kernel@collabora.com References: <20251015153018.43735-1-loic.molinari@collabora.com> <20251015153018.43735-4-loic.molinari@collabora.com> Content-Language: fr From: =?UTF-8?Q?Lo=C3=AFc_Molinari?= Organization: Collabora Ltd In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi Matthew, On 15/10/2025 19:27, Matthew Wilcox wrote: > On Wed, Oct 15, 2025 at 05:30:07PM +0200, Loïc Molinari wrote: > > This looks fine, no need to resend to fix this, but if you'd written > the previous patch slightly differently, you'd've reduced the amount of > code you moved around in this patch, which would have made it easier to > review. > >> + /* Map a range of pages around the faulty address. */ >> + do { >> + pfn = page_to_pfn(pages[start_pgoff]); >> + ret = vmf_insert_pfn(vma, addr, pfn); >> + addr += PAGE_SIZE; >> + } while (++start_pgoff <= end_pgoff && ret == VM_FAULT_NOPAGE); > > It looks to me like we have an opportunity to do better here by > adding a vmf_insert_pfns() interface. I don't think we should delay > your patch series to add it, but let's not forget to do that; it can > have very good performnce effects on ARM to use contptes. Agreed. I initially wanted to provide such an interface based on set_ptes() to benefit from arm64 contptes but thought it'd better be a distinct patch series. > >> @@ -617,8 +645,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) > [...] >> >> - ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page)); >> + if (drm_gem_shmem_map_pmd(vmf, vmf->address, pages[page_offset])) { >> + ret = VM_FAULT_NOPAGE; >> + goto out; >> } > > Does this actually work? Yes, it does. Huge pages are successfully mapped from both map_pages and fault handlers. Anything wrong with it? There seems to be an another issue thought. There are failures [1], all looking like that one [2]. I think it's because map_pages is called with the RCU read lock taken and the DRM GEM map_pages handler must lock the GEM object before accessing pages with dma_resv_lock(). The locking doc says: "If it's not possible to reach a page without blocking, filesystem should skip it.". Unlocking the RCU read lock in the handler seems wrong and doing without a map_pages implementation would be unfortunate. What would you recommend here? Loïc [1] https://patchwork.freedesktop.org/series/156001/ [2] https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_156001v1/bat-dg1-7/igt@vgem_basic@dmabuf-mmap.html