On Mon, Jul 16, 2007 at 03:53:18PM +0400, Sergey Rogozhkin wrote: > >Big loud bell began ringing. The RM7000 fetches and decodes multiple > >instructions in one go. And just like the E9000 cores it does > >throw an exception if it doesn't like one of the opcodes even if that > >doesn't actually get executed. The kernel has a workaround for this > >PMC-Sierra peculiarity (I call it a bug) but it's only being activated > >for E9000 platforms. > > We have had a similar problems with shell on RM7000 based system. It > seems, the reason listed above is only half of the problem, another is: > linux works incorrectly with RM7000 caches hierarchy. One visible effect > is errors in userspace on signal delivery trampolines. > Lets imagine we deliver a signal to application: we write signal > trampoline instructions to stack, writeback (and invalidate) > corresponding dcache line, invalidate corresponding icache line. Thats > all, and we think that we can safely execute the trampoline, but this is > wrong on RM7000! Our trampoline is now in scache, and everything seems > to be ok, but after some number of load/stores corresponding scache line > can be moved to dcache, replaced in scache by another data and not > written to memory (this is a feature of RM7000 caches, its dcache is not > a subset of scache, you can find a possible scenario of similar (but not > the same) cache line transference in RM7000 manual (7.1.5 Orphaned Cache > Lines)). After that it is possible that on signal trampoline execution > icache fetch old memory content instead of instruction written. If we > want to execute instruction written by cpu, we must not only writeback > corresponding dcache lines, but also writeback corresponding scache > lines after it. The error is very sensitively to kernel/user code and > data arrangement, it can be visible with one kernel configuration and > irreproducible with another. > The problem affects not only signal trampoline flush to memory, but most > cases of icache invalidation in kernel. Hmm... Makes sense. I guess I can cook up a patch based on that analysis. Thanks! Ralf
