On Sun, Mar 29, 2015 at 11:12 PM, Andy Lutomirski <[email protected]> wrote: > On Sun, Mar 29, 2015 at 12:36 PM, Denys Vlasenko > <[email protected]> wrote: >> The instruction would need a differentiator whether returned-to code >> is 64-bit or 32-bit. >> Then it probably can use the same approach SYSRET{O,L} uses: >> with REX.W, return is to 64-bit; without it, return is to 32-bit. >> >> Interrupt return then can check pt_regs->cs and use >> IRETL_FAST if it is USER32_CS; use IRETQ_FAST if it is USER_CS >> or KERNEL_CS; otherwise, fall back to slow but "universal" IRETQ.
Hmm. In fact since we'd need such checks, then instructions can be even simpler: they don't even need to check CPL, it can be hardcoded too. We'd need four instructions then: return to 64 and to 32 bits, to CPL0 and to CPL3. >> Do we have contacts at Intel to petition for this? :D > > Some of us do and have petitioned :) And what did Intel say? If there's any interest in doing this, Intel better *do* talk to us before they commit to implementing it. Their track record in implementing "fast syscalls" is nothing to write home about. SYSENTER is a design disaster; SYSRET is buggy. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
