On Thu, Nov 5, 2015 at 1:11 AM, Jason Harmening <jason.harmen...@gmail.com> wrote: > > On Wed, Nov 4, 2015 at 2:17 PM, Svatopluk Kraus <onw...@gmail.com> wrote: >> >> 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(). > > > I like the idea of storing off the physical address. If you want to save > space in the sync list, I think you can place busaddr and pages in a union, > using vaddr == 0 to select which field to use. Some people frown upon use > of unions, though. > > Any reason the panics on PHYS_TO_VM_PAGE in load_buffer() and load_phys() > shouldn't be KASSERTs instead?
KASSERTs are fine. I have looked at Michal's patch again and only KASSERT should be in load_phys() as such buffers are unmapped, temporary mapping must be used and so, they must be in vm_page_array. And maybe some inline function for getting PA from sync list would be nice too. I would like to review final patch if you are going to make it. And it would be nice if Ganbold will test it. Phabricator? _______________________________________________ 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"
