Messages in this thread | | | Subject | Re: [PATCH] iommu/mediatek: Use totalram_pages to setup enable_4GB | From | David Hildenbrand <> | Date | Thu, 4 Jun 2020 10:25:15 +0200 |
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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.
but ... I don't know if I understood what "enable_4GB" needs/implies ... I don't know if this is applicable to VMs at all (on real HW such memory hotplug setups should not exist) ... I don't know how this code would react to memory hotplug, so if the condition changes after the driver loaded and enable_4GB would suddenly apply. Again, most probably not relevant on real HW, only for VMs.
-- Thanks,
David / dhildenb
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