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 <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: >
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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
