From: David Hildenbrand <david@redhat.com>
To: Miles Chen <miles.chen@mediatek.com>
Cc: wsd_upstream@mediatek.com, linux-kernel@vger.kernel.org,
Chao Hao <chao.hao@mediatek.com>,
iommu@lists.linux-foundation.org,
linux-mediatek@lists.infradead.org,
Matthias Brugger <matthias.bgg@gmail.com>,
yingjoe.chen@mediatek.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] iommu/mediatek: Use totalram_pages to setup enable_4GB
Date: Thu, 4 Jun 2020 13:32:40 +0200 [thread overview]
Message-ID: <f02c8c9d-ed75-6513-f8a9-a2fdbb11b750@redhat.com> (raw)
In-Reply-To: <1591264174.12661.17.camel@mtkswgap22>
On 04.06.20 11:49, Miles Chen wrote:
> On Thu, 2020-06-04 at 10:25 +0200, David Hildenbrand wrote:
>> On 04.06.20 10:01, Miles Chen wrote:
>>> To build this driver as a kernel module, we cannot use
>>> the unexported symbol "max_pfn" to setup enable_4GB.
>>>
>>> Use totalram_pages() instead to setup enable_4GB.
>>>
>>> Suggested-by: Mike Rapoport <rppt@linux.ibm.com>
>>> Signed-off-by: Miles Chen <miles.chen@mediatek.com>
>>> Cc: David Hildenbrand <david@redhat.com>
>>> Cc: Yong Wu <yong.wu@mediatek.com>
>>> Cc: Chao Hao <chao.hao@mediatek.com>
>>> ---
>>> drivers/iommu/mtk_iommu.c | 5 ++---
>>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
>>> index 5f4d6df59cf6..c2798a6e0e38 100644
>>> --- a/drivers/iommu/mtk_iommu.c
>>> +++ b/drivers/iommu/mtk_iommu.c
>>> @@ -3,7 +3,6 @@
>>> * Copyright (c) 2015-2016 MediaTek Inc.
>>> * Author: Yong Wu <yong.wu@mediatek.com>
>>> */
>>> -#include <linux/memblock.h>
>>> #include <linux/bug.h>
>>> #include <linux/clk.h>
>>> #include <linux/component.h>
>>> @@ -626,8 +625,8 @@ static int mtk_iommu_probe(struct platform_device *pdev)
>>> return -ENOMEM;
>>> data->protect_base = ALIGN(virt_to_phys(protect), MTK_PROTECT_PA_ALIGN);
>>>
>>> - /* Whether the current dram is over 4GB */
>>> - data->enable_4GB = !!(max_pfn > (BIT_ULL(32) >> PAGE_SHIFT));
>>> + /* Whether the current dram is over 4GB, note: DRAM start at 1GB */
>>> + data->enable_4GB = !!(totalram_pages() > ((SZ_2G + SZ_1G) >> PAGE_SHIFT));
>>
>> A similar thing seems to be done by
>> drivers/media/platform/mtk-vpu/mtk_vpu.c:
>> vpu->enable_4GB = !!(totalram_pages() > (SZ_2G >> PAGE_SHIFT));
>>
>> I do wonder if some weird memory hotplug setups might give you false
>> negatives.
>>
>> E.g., start a VM with 1GB and hotplug 1GB - it will be hotplugged on
>> x86-64 above 4GB, turning max_pfn into 5GB. totalram_pages() should
>> return something < 2GB.
>>
>> Same can happen when you have a VM and use ballooning to fake-unplug
>> memory, making totalram_pages() return something < 4GB, but leaving
>> usable pfns >= 4GB
>
> Yes. Yingjoe also told me that this patch is not correct.
>
> Thanks for pointing this out. totalram_pages() does not work
> for some cases:
>
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).
--
Thanks,
David / dhildenb
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next prev parent reply other threads:[~2020-06-04 11:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-04 8:01 [PATCH] iommu/mediatek: Use totalram_pages to setup enable_4GB Miles Chen
2020-06-04 8:25 ` David Hildenbrand
2020-06-04 9:49 ` Miles Chen
2020-06-04 11:32 ` David Hildenbrand [this message]
2020-06-04 15:06 ` Christoph Hellwig
2020-06-04 15:27 ` David Hildenbrand
2020-06-05 12:52 ` David Hildenbrand
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