> Am 26.08.2020 um 20:03 schrieb Andy Lutomirski <luto@xxxxxxxxxx>: > >> 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. I like that option much better than the orig_ax hacks. Is this going to be something useable enough for stable? Also, Thomas, will you have a look at moving the vector info? If so, I'd hold still on this patch for a bit. Alex Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
