Messages in this thread |  | | Date | Fri, 24 Jan 2020 23:00:08 +0000 | From | Ashish Kalra <> | Subject | Re: [PATCH v2] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests. |
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On Tue, Jan 21, 2020 at 03:54:03PM -0500, Konrad Rzeszutek Wilk wrote: > > > > Additional memory calculations based on # of PCI devices and > > their memory ranges will make it more complicated with so > > many other permutations and combinations to explore, it is > > essential to keep this patch as simple as possible by > > adjusting the bounce buffer size simply by determining it > > from the amount of provisioned guest memory. >> >> Please rework the patch to: >> >> - Use a log solution instead of the multiplication. >> Feel free to cap it at a sensible value.
Ok.
>> >> - Also the code depends on SWIOTLB calling in to the >> adjust_swiotlb_default_size which looks wrong. >> >> You should not adjust io_tlb_nslabs from swiotlb_size_or_default.
>> That function's purpose is to report a value. >> >> - Make io_tlb_nslabs be visible outside of the SWIOTLB code. >> >> - Can you utilize the IOMMU_INIT APIs and have your own detect which would >> modify the io_tlb_nslabs (and set swiotbl=1?).
This seems to be a nice option, but then IOMMU_INIT APIs are x86-specific and this swiotlb buffer size adjustment is also needed for other memory encryption architectures like Power, S390, etc.
>> >> Actually you seem to be piggybacking on pci_swiotlb_detect_4gb - so >> perhaps add in this code ? Albeit it really should be in it's own >> file, not in arch/x86/kernel/pci-swiotlb.c
Actually, we piggyback on pci_swiotlb_detect_override which sets swiotlb=1 as x86_64_start_kernel() and invocation of sme_early_init() forces swiotlb on, but again this is all x86 architecture specific.
Thanks, Ashish
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