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bh=A8kNEVeRCF9+y3k5ZAIQfT6doRtq7dwlic2ox+e/gW4=; b=VQCAfW+E+2zzTIA2q7fl4CNhsLRj8mqleSCdQwEOPDACiazeODfe1erklKQk+eNBXHBXYX Wu3Yflca3ko2MKcIRDyWbUt1f/5xjKzOPM42PRhZmTzgCHh5g6480mf9PwbIySwSG6AYKc jHGD7G3gbYd1tb5PDRlDZm3XCVW8Hl4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-392-fR5KWv9UPeW1nysCpKfoew-1; Fri, 05 Jun 2020 08:52:38 -0400 X-MC-Unique: fR5KWv9UPeW1nysCpKfoew-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3807C100AA2C; Fri, 5 Jun 2020 12:52:36 +0000 (UTC) Received: from [10.36.114.72] (ovpn-114-72.ams2.redhat.com [10.36.114.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5830B891C1; Fri, 5 Jun 2020 12:52:33 +0000 (UTC) Subject: Re: [PATCH] iommu/mediatek: Use totalram_pages to setup enable_4GB From: David Hildenbrand To: Christoph Hellwig References: <20200604080120.2628-1-miles.chen@mediatek.com> <55820901-430b-14c4-9426-7a4991ca0eed@redhat.com> <1591264174.12661.17.camel@mtkswgap22> <20200604150643.GA29193@infradead.org> Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Cc: wsd_upstream@mediatek.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Chao Hao , Miles Chen , linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Matthias Brugger , yingjoe.chen@mediatek.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 04.06.20 17:27, David Hildenbrand wrote: > On 04.06.20 17:06, Christoph Hellwig wrote: >> On Thu, Jun 04, 2020 at 01:32:40PM +0200, David Hildenbrand wrote: >>> Just a thought: If memory hotplug is applicable as well, you might >>> either want to always assume data->enable_4GB, or handle memory hotplug >>> events from the memory notifier, when new memory gets onlined (not sure >>> how tricky that is). >> >> We probably want a highest_pfn_possible() or similar API instead of >> having drivers poking into random VM internals. > > Well, memory notifiers are a reasonable api used accross the kernel to > get notified when new memory is onlined to the buddy that could be used > for allocations. > > highest_pfn_possible() would have to default to something linked to > MAX_PHYSMEM_BITS whenever memory hotplug is configured, I am not sure > how helpful that is (IOW, you can just default to enable_4GB=true in > that case instead in most cases). Correction: At least on x86-64 we have max_possible_pfn, which will consult the ACPI SRAT table to figure out the maximum possible PFN. (Without SRAT, max_possible_pfn will point at the end of initial boot memory and not consider hotplug memory - something that e.g., newer QEMU versions work around by creating SRAT tables if memory hotplug might be possible, even if there is no actual NUMA configuration). pci-swiotlb.c similarly relies on that to figure out if there are any !DMA addresses to handle. -- Thanks, David / dhildenb _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu