On Wed, Aug 26, 2020 at 10:47 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > Andy, > > On Wed, Aug 26 2020 at 09:13, Andy Lutomirski wrote: > > On Wed, Aug 26, 2020 at 7:27 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > >> The below nasty hack cures it, but I hate it with a passion. I'll look > >> deeper for a sane variant. > >> > > Fundamentally, the way we overload orig_ax is problematic. I have a > > half-written series to improve it, but my series is broken. I think > > it's fixable, though. > > > > First is this patch to use some __csh bits to indicate the entry type. > > As far as I know, this patch is correct: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry&id=dfff54208072a27909ae97ebce644c251a233ff2 > > Yes, that looks about right. > > > Then I wrote this incorrect patch: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry&id=3a5087acb8a2cc1e88b1a55fa36c2f8bef370572 > > > > That one is wrong because the orig_ax wreckage seems to have leaked > > into user ABI -- user programs think that orig_ax has certain > > semantics on user-visible entries. > > Yes, orig_ax is pretty much user ABI for a very long time. > > > But I think that the problem in this thread could be fixed quite > > nicely by the first patch, plus a new CS_ENTRY_IRQ and allocating > > eight bits of __csh to store the vector. Then we could read out the > > vector. > > That works. Alternatively I can just store the vector in the irq > descriptor itself. That's trivial enough and can be done completely in C > independent of the stuff above. The latter sounds quite sensible to me. It does seem vaguely ridiculous to be trying to fish the vector out of pt_regs in the APIC code. --Andy
