I’ve been attempting to use kexec to write a network bootloader for an Acer R13 Chromebook. I initially tried on a 5.8.7 kernel, then moved on to 5.9-rc4 to see if that fixed the problem (spoiler: it didn’t).
When booted from kexec (instead of the native u-boot), the console is flooded with IOMMU fault messages (fortunately rate limited!) like these:
Code:
[ +0.001401] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xffb39000 pa=0xb6d39500 larb=0 port=0 layer=0 read
[ +0.001402] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xffbe4000 pa=0xb6de4400 larb=0 port=0 layer=0 read
[ +0.001377] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xffc90000 pa=0xb6e90400 larb=0 port=0 layer=0 read
[ +0.001357] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xffd3a000 pa=0xb6f3a500 larb=0 port=0 layer=0 read
[ +0.001342] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xffde0000 pa=0xb6fe0e00 larb=0 port=0 layer=0 read
[ +0.001336] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xffe86000 pa=0xb6886b00 larb=0 port=0 layer=0 read
[ +0.001316] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xfff2b001 pa=0xb7d5b700 larb=0 port=0 layer=1 read
[ +0.001323] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xfffcf001 pa=0xb7dff200 larb=0 port=0 layer=1 read
[ +0.001325] mtk-iommu 10205000.iommu: fault type=0x4 iova=0xff861000 pa=0xb7e61380 larb=0 port=0 layer=0 read
[ +4.991802] mtk_iommu_isr: 1209385 callbacks suppressed
That’s a log of suppressed messages, and a similar block is printed every 5 seconds.
The system appears to be perfectly functional otherwise, but the kernel is using ~70% of a CPU core at idle as opposed to ~10% after a non-kexec boot (as reported by htop).
So far I’ve identified
mtk_iommu_isr as the source of the message, and a call to
domain->handler(...) in
report_iommu_fault as responsible for the status code triggering the message. I’m still struggling to figure out where that handler is registered though.
Does anyone have any suggestions as to how I could go about getting to the bottom of this?
PS: I hope this is the right place to post this. If not, please let me know!
