Messages in this thread | | | Date | Mon, 29 Jun 2015 21:46:33 +0200 | Subject | Re: [PATCH v4 00/17] x86: Rewrite exit-to-userspace code | From | Richard Weinberger <> |
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Andy,
On Mon, Jun 29, 2015 at 9:33 PM, Andy Lutomirski <luto@kernel.org> wrote: > This is the first big batch of x86 asm-to-C conversion patches. > > The exit-to-usermode code is copied in several places and is written > in a nasty combination of asm and C. It's not at all clear what > it's supposed to do, and the way it's structured makes it very hard > to work with. For example, it's not even clear why syscall exit > hooks are called only once per syscall right now. (It seems to be a > side effect of the way that rdi and rdx are handled in the asm loop, > and it seems reliable, but it's still pointlessly complicated.) The > existing code also makes context tracking overly complicated and > hard to understand. Finally, it's nearly impossible for anyone to > change what happens on exit to usermode, since the existing code is > so fragile. > > I tried to clean it up incrementally, but I decided it was too hard. > Instead, this series just replaces the code. It seems to work. > > Context tracking in particular works very differently now. The > low-level entry code checks that we're in CONTEXT_USER and switches > to CONTEXT_KERNEL. The exit code does the reverse. There is no > need to track what CONTEXT_XYZ state we came from, because we > already know. Similarly, SCHEDULE_USER is gone, since we can > reschedule if needed by simply calling schedule() from C code. > > The main things that are missing are that I haven't done the 32-bit > parts (anyone want to help?) and therefore I haven't deleted the old > C code. I also think this may break UML for trivial reasons. > > IRQ context tracking is still messy. One the cleanup progresses > to the point that we can enter CONTEXT_KERNEL in syscalls before > enabling interrupts, we can fully clean up IRQ context tracking. > > Once these land, I'll send some more :) > > Note: we might want to backport patches 1 and 2. > > Changes from v3: > - Add the syscall_arg_fault_32 test. > - Fix a pre-existing bad syscall arg buglet. > - Fix an asm glitch due to a bad rebase. > - Fix a CONFIG_PROVE_LOCKDEP warning. > Borislav: the end result of this series differs from the v3.91 that I > only in the removal of a single trailing tab. The badarg patch is in > a different place now, though, since we might want to backport it. > > Changes from v2: Misplaced the actual list -- sorry. > > Changes from v1: > - Fix bisection failure by squashing the 64-bit native and compat syscall > conversions together. The intermediate state didn't built, and fixing > it isn't worthwhile (the results will be harder to understand). > - Replace context_tracking_assert_state with CT_WARN_ON and ct_state. > - The last two patches are now. I incorrectly thought that we weren't > ready for them yet on 32-bit kernels, but I was wrong. > > Andy Lutomirski (16): > selftests/x86: Add a test for 32-bit fast syscall arg faults > x86/entry/64/compat: Fix bad fast syscall arg failure path > context_tracking: Add ct_state and CT_WARN_ON > notifiers: Assert that RCU is watching in notify_die > x86: Move C entry and exit code to arch/x86/entry/common.c > x86/traps: Assert that we're in CONTEXT_KERNEL in exception entries > x86/entry: Add enter_from_user_mode and use it in syscalls > x86/entry: Add new, comprehensible entry and exit hooks > x86/entry/64: Really create an error-entry-from-usermode code path > x86/entry/64: Migrate 64-bit and compat syscalls to new exit hooks > x86/asm/entry/64: Save all regs on interrupt entry > x86/asm/entry/64: Simplify irq stack pt_regs handling > x86/asm/entry/64: Migrate error and interrupt exit work to C > x86/entry: Remove exception_enter from most trap handlers > x86/entry: Remove SCHEDULE_USER and asm/context-tracking.h > x86/irq: Document how IRQ context tracking works and add an assertion > > Ingo Molnar (1): > uml: Fix do_signal() prototype
Do you have a git tree for that?
-- Thanks, //richard
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