Hello Konrad, On Tue, Jun 23, 2020 at 09:38:43AM -0400, Konrad Rzeszutek Wilk wrote: > On Mon, Apr 27, 2020 at 06:53:18PM +0000, Ashish Kalra wrote: > > Hello Konrad, > > > > On Mon, Mar 30, 2020 at 10:25:51PM +0000, Ashish Kalra wrote: > > > Hello Konrad, > > > > > > On Tue, Mar 03, 2020 at 12:03:53PM -0500, Konrad Rzeszutek Wilk wrote: > > > > On Tue, Feb 04, 2020 at 07:35:00PM +0000, Ashish Kalra wrote: > > > > > Hello Konrad, > > > > > > > > > > Looking fwd. to your feedback regarding support of other memory > > > > > encryption architectures such as Power, S390, etc. > > > > > > > > > > Thanks, > > > > > Ashish > > > > > > > > > > On Fri, Jan 24, 2020 at 11:00:08PM +0000, Ashish Kalra wrote: > > > > > > 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. > > > > > > > > Oh dear. That I hadn't considered. > > > > > > > > > > > > >> > > > > > > >> 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. > > > > > > > > Then it looks like the best bet is to do it from within swiotlb_init? > > > > We really can't do it from swiotlb_size_or_default - that function > > > > should just return a value and nothing else. > > > > > > > > > > Actually, we need to do it in swiotlb_size_or_default() as this gets > > > called by > > > reserve_crashkernel_low() in arch/x86/kernel/setup.c and used to > > > reserve low crashkernel memory. If we adjust swiotlb size later in > > > swiotlb_init() which gets called later than reserve_crashkernel_low(), > > > then any swiotlb size changes/expansion will conflict/overlap with the > > > low memory reserved for crashkernel. > > > > > and will also potentially cause SWIOTLB buffer allocation failures. > > > > Do you have any feedback, comments on the above ? > > > The init boot chain looks like this: > > initmem_init > pci_iommu_alloc > -> pci_swiotlb_detect_4gb > -> swiotlb_init > > reserve_crashkernel > reserve_crashkernel_low > -> swiotlb_size_or_default > .. > > > (rootfs code): > pci_iommu_init > -> a bunch of the other IOMMU late_init code gets called.. > -> pci_swiotlb_late_init > > I have to say I am lost to how your patch fixes "If we adjust swiolb > size later .. then any swiotlb size .. will overlap with the low memory > reserved for crashkernel"? >
Actually as per the boot flow : setup_arch() calls reserve_crashkernel() and pci_iommu_alloc() is invoked through mm_init()/mem_init() and not via initmem_init(). start_kernel: ... setup_arch() reserve_crashkernel reserve_crashkernel_low -> swiotlb_size_or_default ... ... mm_init() mem_init() pci_iommu_alloc -> pci_swiotlb_detect_4gb -> swiotlb_init So as per the above boot flow, reserve_crashkernel() can get called before swiotlb_detect/init, and hence, if we don't fixup or adjust the SWIOTLB buffer size in swiotlb_size_or_default() then crash kernel will reserve memory which will conflict/overlap with any SWIOTLB bounce buffer allocated memory (adjusted or fixed up later). Therefore, we need to adjust/fixup SWIOTLB bounce buffer memory in swiotlb_size_or_default() function itself, before swiotlb detect/init funtions get invoked. Thanks, Ashish > Or are you saying that 'reserve_crashkernel_low' is the _culprit_ and it > is the one changing the size? And hence it modifying the swiotlb size > will fix this problem? Aka _before_ all the other IOMMU get their hand > on it? > > If so why not create an > IOMMU_INIT(crashkernel_adjust_swiotlb,pci_swiotlb_detect_override, > NULL, NULL); > > And crashkernel_adjust_swiotlb would change the size of swiotlb buffer > if conditions are found to require it. > > You also may want to put a #define DEBUG in arch/x86/kernel/pci-iommu_table.c > to check out whether the tree structure of IOMMU entries is correct. > > > > But still I am lost - if say the AMD one does decide for unknown reason > to expand the SWIOTLB you are still stuck with the 'overlap with > the low memory reserved' or so. > > Perhaps add a late_init that gets called as the last one to validate > this ? And maybe if the swiotlb gets turned off you also take proper > steps? > > > As such i feel, this patch is complete otherwise and can be included as > > it is. > > > > Thanks, > > Ashish _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu