From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sender4-pp-f112.zoho.com (sender4-pp-f112.zoho.com [136.143.188.112]) (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 BA5991974FE for ; Sun, 19 Jan 2025 20:23:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.112 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737318235; cv=pass; b=P6Ntsn6SZr0gFbaHdDXn2iTTCLOfUz00HqhiyxBj/RBg1tyPZRW6EaRHUnyz06rsBB4ZfowbQMKI4LIcjyrBtAw0M9kD/AySej7/iDpeZujUPNb0aXMUkHYyWsLj1zDdwLNk7TiHuL91Bq1uf/umOaYs4WnRZW5gDYEMHKlhtsk= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737318235; c=relaxed/simple; bh=tWfSI+1MtUACMBfnv4RFYgj8AtEb/70TFPYM8QfC13U=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=VxqK8kyJPl6Ch45VElmfioeIbnQI/UkEL1oEYP4oHND7Cu7SCKUzu9R5hFCCxT1ryJCshVX/9YjZ6bTohVX3OlxVOiGPWm4Tm2D+GCP05tFCMSFKVt5DDG6I4UNRFY+fKsHpzuVBchjXBWPlfiwmzeQDUPX+ovGlsFPKfS3h8Ac= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (1024-bit key) header.d=collabora.com header.i=dmitry.osipenko@collabora.com header.b=P3C4eoQQ; arc=pass smtp.client-ip=136.143.188.112 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 (1024-bit key) header.d=collabora.com header.i=dmitry.osipenko@collabora.com header.b="P3C4eoQQ" ARC-Seal: i=1; a=rsa-sha256; t=1737318217; cv=none; d=zohomail.com; s=zohoarc; b=FcVt7sT55FRfJnB7hDpCceMyLgXI6PVICfZtYwJVkQz7FG8zkQ3pH/cw22u5+cqY4MCqarQPX/j4Pw6/U08oJUKVwZ/IQ5vz8jmKUxrny6grkPp3MvGJcREbUuogE8IM5X4JahjxaDSqB3+l8n9E5+sUiym+cX2D2QmeZBPPngk= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1737318217; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:Subject:To:To:Message-Id:Reply-To; bh=UPtfCtUKIAnqCQybAVHnv01lXRb06TK7ijHh2KLOKpk=; b=QLyDDeQzWVmPkipHItdkWgXSEjyJez6LsV5kHK32jNeu/pFZK3gTBcXX+Mau9EQNL2VZNJUwCX2NMTOr3Y3ce0VJiuPHqY6aSeixCGNPYktysV2jWK00TsNh5kVNc+sT6jnnRMX4IZHttStq0v2axsJFCAwbyExVi8mshKHpn7c= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=collabora.com; spf=pass smtp.mailfrom=dmitry.osipenko@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1737318217; s=zohomail; d=collabora.com; i=dmitry.osipenko@collabora.com; h=Message-ID:Date:Date:MIME-Version:Subject:Subject:From:From:To:To:Cc:Cc:References:In-Reply-To:Content-Type:Content-Transfer-Encoding:Message-Id:Reply-To; bh=UPtfCtUKIAnqCQybAVHnv01lXRb06TK7ijHh2KLOKpk=; b=P3C4eoQQZOIsO+77wHpza70B2I5iAoJtkIEYKhtBrRp4mn6L5IqcwdxR0B7MG3w6 63xUpCIPNfPlm7Q6BDiPYN15kJuLXgbV4vFTPZWEYW9LRkjxD40C22KaE0tc0DgwpG1 HRYedFS/q1ASzNpgD/AfVtQzWtYcdTGN3yLdcTiM= Received: by mx.zohomail.com with SMTPS id 1737318215647463.5943389283731; Sun, 19 Jan 2025 12:23:35 -0800 (PST) Message-ID: <0820162d-f6d2-400e-b14b-86954d475d37@collabora.com> Date: Sun, 19 Jan 2025 23:23:31 +0300 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] drm/virtio: Support partial maps of GEM objects From: Dmitry Osipenko To: Sasha Finkelstein Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Simona Vetter , dri-devel@lists.freedesktop.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, asahi@lists.linux.dev References: <20250109-virtgpu-gem-partial-map-v1-1-a914b48776bd@gmail.com> <2f51584c-0590-432b-a4db-7a2af99cde15@collabora.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ZohoMailClient: External On 1/19/25 23:02, Dmitry Osipenko wrote: > On 1/19/25 19:18, Sasha Finkelstein wrote: >> On Sun, 19 Jan 2025 at 12:50, Dmitry Osipenko >> wrote: >>>> ret = io_remap_pfn_range(vma, vma->vm_start, >>>> - vram->vram_node.start >> PAGE_SHIFT, >>>> + (vram->vram_node.start >> PAGE_SHIFT) + vma->vm_pgoff, >>>> vm_size, vma->vm_page_prot); >>>> return ret; >>>> } >>> >>> The vma->vm_pgoff is fake in DRM, it's used for looking up DRM GEM >>> object based on the vma->vm_pgoff value when mmap is invoked. >> >> If my understanding is correct, vm_pgoff gets "unfaked" by >> https://elixir.bootlin.com/linux/v6.12.6/source/drivers/gpu/drm/virtio/virtgpu_vram.c#L48 >> >>> vma->vm_pgoff should be treated as zero here. Hence we can map a part of >>> GEM, but only from its start. See drm_gem_mmap(). >> >> I've had a "v0" (not on ml) of this patch that always treated vma->vm_pgoff as >> zero. This broke when anything tried to mmap with a non-zero offset. Adding >> vm_pgoff made it work correctly. > > I've tested this patch. Partial mapping with a non-zero offset doesn't > work because drm_gem_mmap() rejects it. I'd want to see your sample code > that performs mmaping, maybe I'm missing something. > >>> Please correct vma->vm_pgoff in v2. >> >> I need apps to be able to mmap with a non-zero offset for my usecase. >> While the correct value may be something else other than what is in >> the current patch, 0 is definitely incorrect for at least some workloads. > > drm_gem_mmap() uses drm_vma_offset_exact_lookup_locked() that doesn't > allow vma->vm_pgoff != node.start. AFAICT, no one driver supports > mapping with a non-zero offset, perhaps for a reason that I don't know > about. See now that a non-zero mapping of a dmabuf might work. Will test it. -- Best regards, Dmitry