Messages in this thread | | | Date | Tue, 10 Oct 2006 13:31:28 +0100 | From | Christoph Hellwig <> | Subject | Re: ptrace and pfn mappings |
| |
On Tue, Oct 10, 2006 at 11:16:27AM +1000, Benjamin Herrenschmidt wrote: > And the last of my "issues" here: > > get_user_pages() can't handle pfn mappings, thus access_process_vm() > can't, and thus ptrace can't. When they were limited to dodgy /dev/mem > things, it was probably ok. But with more drivers needing that, like the > DRM, sound drivers, and now with SPU problem state registers and local > store mapped that way, it's becoming a real issues to be unable to > access any of those mappings from gdb. > > The "easy" way out I can see, but it may have all sort of bad side > effects I haven't thought about at this point, is to switch the mm in > access_process_vm (at least if it's hitting such a VMA).
Switching the mm is definitly no acceptable. Too many things could break when violating the existing assumptions.
> That do you guys think ? Any better idea ? The problem with mappings > like what SPUfs or the DRM want is that they can change (be remapped > between HW and backup memory, as described in previous emails), thus we > don't want to get struct pages even if available and peek at them as > they might not be valid anymore, same with PFNs (we could imagine > ioremap'ing those PFN's but that would be racy too). The only way that > is guaranteed not to be racy is to do exactly what a user do, that is do > user accesses via the target process vm itself....
I think the best idea is to add a new ->access method to the vm_operations that's called by access_process_vm() when it exists and VM_IO or VM_PFNMAP are set. ->access would take the required object locks and copy out the data manually. This should work both for spufs and drm. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |