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? _______________________________________________ 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"
