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 <r...@linux.ibm.com> > > Signed-off-by: Miles Chen <miles.c...@mediatek.com> > > Cc: David Hildenbrand <da...@redhat.com> > > Cc: Yong Wu <yong...@mediatek.com> > > Cc: Chao Hao <chao....@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...@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: e.g., DRAM start @0x4000_0000 and DRAM size is 0x1_0000_0000 but we reserve large amount of memory, which makes totalram_pages() < 3GB but it is possible to allocate a pfn >= 4GB. I will discuss this internally. Miles > . > > 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. >
