On Tue, Nov 3, 2015 at 8:45 AM, Jason Harmening <jason.harmen...@gmail.com> wrote: > > On Sun, Nov 1, 2015 at 8:11 AM, Ian Lepore <i...@freebsd.org> wrote: >> >> >> It's almost certainly not related to sysinit ordering. This exception >> is happening during mmc probing after interrupts are enabled. >> >> It appears that the problem is the faulting code is running on one of >> the very early pre-allocated kernel stacks (perhaps in an interrupt >> handler on an idle thread stack), and these stacks are not in memory >> represented in the vm page arrays. The mmc code is using a 64-byte >> buffer on the stack and mapping it for DMA. Normally that causes a >> bounce for cacheline alignment, but unluckily in this case that buffer >> on the stack just happened to be aligned to a cacheline boundary and a >> multiple of the cacheline size, so no bounce. That causes the new sync >> logic that is based on keeping vm_page_t pointers and offsets to get a >> NULL pointer back from PHYS_TO_VM_PAGE when mapping, then it dies at >> sync time trying to dereference that. It used to work because the sync >> logic used to use the vaddr, not a page pointer. >> >> Michal was working on a patch yesterday. >> > > Ah, thanks for pointing that out Ian. I was left scratching my head > (admittedly on the road and w/o easy access to the code) wondering what on > earth would be trying to do DMA during SI_SUB_CPU. >
Using of fictitious pages is not so easy here as in case pointed by kib@ where they are allocated and freed inside one function. For sync list sake, they must be allocated when a buffer is loaded and freed when is unloaded. Michal uses pmap_kextract() in case when KVA of buffer is not zero in his proof-of-concept patch: https://gist.github.com/strejda/d5ca3ed202427a2e0557 When KVA of buffer is not zero, temporary mapping is not used at all, so vm_page_t array is not needed too. IMO, buffer's physical address can be saved in sync list to be used when its KVA is not zero. Thus pmap_kextract() won't be called in dma_dcache_sync(). _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
