On Wed, Nov 29, 2017 at 1:25 PM, Andy Lutomirski <[email protected]> wrote: > > >> On Nov 29, 2017, at 12:58 PM, Linus Torvalds <[email protected]> >> wrote: >> >>> On Wed, Nov 29, 2017 at 10:12 AM, Andy Lutomirski <[email protected]> wrote: >>> >>> Jarkko, can you try the attached patch? If it survives resume, can >>> you see if the log contains anything interesting? >> >> I'm not Jarkko, but I'm not a huge fan of that patch. >> >> If this was the cause of the problem (and it looks likely), wouldn't >> it be nicer to instead make sure that __restore_processor_state() is >> made to use only low-level code and easy to verify? >> >> That function is already marked "notrace" because it is so fragile, >> and it does the segment register reloads manually with inline asms. > > I completely agree, and I think it might be better to move more of that crap > to asm. Also, it looks quite buggy -- it restores segment registers before > it loads the LDT, so they had better not be user registers.
It does indeed restore user state. And it very well may need to work on Xen PV, too. Blech. > > Or we could load fixed values into the segment regs if they're not user > values. > >> >> Could we make it use "native_load_gs_index()" instead? Or even go all >> the way and make it do that user-space %gs load internally with inline >> asm, the way it already does the kernel space %gs? > > Dunno. If we need the exception handling, it can't be inlined. > > Anyway, this wasn't meant to be an upstreamable fix. It was meant to make > sure the problem I'm fixing is the right problem. > >> >> (Maybe "native_wrmsrl()" too?) >> >> Or is this actually all supposed to work even under PV? That sounds really >> iffy. >> >> Linus
