From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org,
Dave Hansen <dave.hansen@linux.intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 42/43] x86/mm/kaiser: Allow KAISER to be enabled/disabled at runtime
Date: Sat, 25 Nov 2017 21:05:20 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.20.1711252100010.2316@nanos> (raw)
In-Reply-To: <47186975-1DCB-4767-8C4C-0816931E3595@amacapital.net>
On Sat, 25 Nov 2017, Andy Lutomirski wrote:
> > On Nov 25, 2017, at 12:18 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> >> On Fri, 24 Nov 2017, Ingo Molnar wrote:
> >>
> >> From: Dave Hansen <dave.hansen@linux.intel.com>
> >>
> >> The KAISER CR3 switches are expensive for many reasons. Not all systems
> >> benefit from the protection provided by KAISER. Some of them can not
> >> pay the high performance cost.
> >>
> >> This patch adds a debugfs file. To disable KAISER, you do:
> >>
> >> echo 0 > /sys/kernel/debug/x86/kaiser-enabled
> >>
> >> and to re-enable it, you can:
> >>
> >> echo 1 > /sys/kernel/debug/x86/kaiser-enabled
> >>
> >> This is a *minimal* implementation. There are certainly plenty of
> >> optimizations that can be done on top of this by using ALTERNATIVES
> >> among other things.
> >
> > It's not only minimal. It's naive and broken. That thing explodes when
> > toggled in the wrong moment. I did not even attempt to debug that, because
> > I think the approach is wrong.
> >
> > If you really want to make it runtime switchable, then:
> >
> > - the shadow tables need to be updated unconditionally. I did not check
> > whether thats done right now, but explosions are simpler to achieve when
> > switching it back on. Though switching it off crashes as well.
> >
> > - you need to make sure that no task is in user space or on the way to it.
> > The much I hate stop_machine(), that's probably the right tool.
> > Once everything is in stomp_machine() the switch can be flipped.
> >
> > - the poisoning/unpoisoning of the kernel tables does not need to be done
> > from stop_machine(). That can be done from regular context with a TIF
> > flag, so you can make sure that every task is up to date before
> > returning to user space. Though that needs a lot of thought.
> >
> > For now I really want to see that removed entirely and replaced by a simple
> > boot time switch. We can use the global variable for now and optimize it
> > later on.
> >
>
> Nah, let's do it right: use either X86_FEATURE_WHATEVER or a
> static_branch. We have nice asm support for both.
Agreed.
> Keep in mind that, for a static_branch, actually setting the thing needs
> to be deferred, but that's straightforward.
That's not an issue during boot. That would be an issue for a run time
switch.
Thanks,
tglx
next prev parent reply other threads:[~2017-11-25 20:05 UTC|newest]
Thread overview: 112+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-24 17:23 [PATCH 00/43] x86 entry-stack and Kaiser series, 2017/11/24, v2 version Ingo Molnar
2017-11-24 17:23 ` [PATCH 01/43] x86/decoder: Add new TEST instruction pattern Ingo Molnar
2017-11-24 17:23 ` [PATCH 02/43] x86/asm/64: Allocate and enable the SYSENTER stack Ingo Molnar
2017-11-24 17:23 ` [PATCH 03/43] x86/dumpstack: Add get_stack_info() support for " Ingo Molnar
2017-11-24 17:23 ` [PATCH 04/43] x86/gdt: Put per-cpu GDT remaps in ascending order Ingo Molnar
2017-11-24 17:23 ` [PATCH 05/43] x86/fixmap: Generalize the GDT fixmap mechanism Ingo Molnar
2017-11-24 17:23 ` [PATCH 06/43] x86/kasan/64: Teach KASAN about the cpu_entry_area Ingo Molnar
2017-11-24 17:23 ` [PATCH 07/43] x86/asm: Fix assumptions that the HW TSS is at the beginning of cpu_tss Ingo Molnar
2017-11-24 17:23 ` [PATCH 08/43] x86/dumpstack: Handle stack overflow on all stacks Ingo Molnar
2017-11-24 17:23 ` [PATCH 09/43] x86/asm: Move SYSENTER_stack to the beginning of struct tss_struct Ingo Molnar
2017-11-24 17:23 ` [PATCH 10/43] x86/asm: Remap the TSS into the cpu entry area Ingo Molnar
2017-11-24 17:23 ` [PATCH 11/43] x86/asm/64: Separate cpu_current_top_of_stack from TSS.sp0 Ingo Molnar
2017-11-24 17:23 ` [PATCH 12/43] x86/espfix/64: Stop assuming that pt_regs is on the entry stack Ingo Molnar
2017-11-24 18:25 ` Borislav Petkov
2017-11-24 19:12 ` Andy Lutomirski
2017-11-26 14:05 ` Ingo Molnar
2017-11-26 17:28 ` Borislav Petkov
2017-11-27 9:19 ` Ingo Molnar
2017-11-24 17:23 ` [PATCH 13/43] x86/asm/64: Use a percpu trampoline stack for IDT entries Ingo Molnar
2017-11-24 19:02 ` Borislav Petkov
2017-11-26 14:16 ` Ingo Molnar
2017-11-24 17:23 ` [PATCH 14/43] x86/asm/64: Return to userspace from the trampoline stack Ingo Molnar
2017-11-24 19:10 ` Borislav Petkov
2017-11-26 14:18 ` Ingo Molnar
2017-11-26 17:33 ` Borislav Petkov
2017-11-24 17:23 ` [PATCH 15/43] x86/entry/64: Create a percpu SYSCALL entry trampoline Ingo Molnar
2017-11-25 11:40 ` Borislav Petkov
2017-11-25 15:00 ` Andy Lutomirski
2017-11-26 14:26 ` [PATCH] " Ingo Molnar
2017-11-24 17:23 ` [PATCH 16/43] x86/irq: Remove an old outdated comment about context tracking races Ingo Molnar
2017-11-25 12:05 ` Borislav Petkov
2017-11-24 17:23 ` [PATCH 17/43] x86/irq/64: In the stack overflow warning, print the offending IP Ingo Molnar
2017-11-25 12:07 ` Borislav Petkov
2017-11-24 17:23 ` [PATCH 18/43] x86/entry/64: Move the IST stacks into cpu_entry_area Ingo Molnar
2017-11-25 12:34 ` Borislav Petkov
2017-11-24 17:23 ` [PATCH 19/43] x86/entry/64: Remove the SYSENTER stack canary Ingo Molnar
2017-11-25 15:29 ` Borislav Petkov
2017-11-24 17:23 ` [PATCH 20/43] x86/entry: Clean up SYSENTER_stack code Ingo Molnar
2017-11-25 16:39 ` Borislav Petkov
2017-11-25 16:50 ` Thomas Gleixner
2017-11-25 16:55 ` Andy Lutomirski
2017-11-25 17:03 ` Thomas Gleixner
2017-11-25 17:10 ` Borislav Petkov
2017-11-25 17:26 ` Andy Lutomirski
2017-11-27 9:27 ` Peter Zijlstra
2017-11-24 17:23 ` [PATCH 21/43] x86/mm/kaiser: Disable global pages by default with KAISER Ingo Molnar
2017-11-24 17:23 ` [PATCH 22/43] x86/mm/kaiser: Prepare assembly for entry/exit CR3 switching Ingo Molnar
2017-11-25 0:02 ` Thomas Gleixner
2017-11-25 12:41 ` Thomas Gleixner
2017-11-26 11:50 ` Borislav Petkov
2017-11-26 14:55 ` [PATCH v2] x86/mm/kaiser: Prepare the x86/entry assembly code " Ingo Molnar
2017-11-27 13:29 ` Josh Poimboeuf
2017-11-27 13:36 ` Thomas Gleixner
2017-11-24 17:23 ` [PATCH 23/43] x86/mm/kaiser: Introduce user-mapped per-cpu areas Ingo Molnar
2017-11-26 17:41 ` Borislav Petkov
2017-11-27 9:26 ` Ingo Molnar
2017-11-27 21:14 ` Dave Hansen
2017-11-24 17:23 ` [PATCH 24/43] x86/mm/kaiser: Mark per-cpu data structures required for entry/exit Ingo Molnar
2017-11-25 17:17 ` Thomas Gleixner
2017-11-26 15:54 ` Ingo Molnar
2017-11-24 17:23 ` [PATCH 25/43] x86/mm/kaiser: Unmap kernel from userspace page tables (core patch) Ingo Molnar
2017-11-26 18:51 ` Borislav Petkov
2017-11-27 9:30 ` Ingo Molnar
2017-11-26 20:49 ` Borislav Petkov
2017-11-27 10:38 ` Ingo Molnar
2017-11-26 22:25 ` [PATCH 25/43] x86/mm/kaiser: Unmap kernel from userspace page tables (core patch), noexec=off Borislav Petkov
2017-11-26 22:41 ` Thomas Gleixner
2017-11-24 17:23 ` [PATCH 26/43] x86/mm/kaiser: Allow NX poison to be set in p4d/pgd Ingo Molnar
2017-11-24 17:23 ` [PATCH 27/43] x86/mm/kaiser: Make sure static PGDs are 8k in size Ingo Molnar
2017-11-24 17:23 ` [PATCH 28/43] x86/mm/kaiser: Map cpu entry area Ingo Molnar
2017-11-25 21:40 ` Thomas Gleixner
2017-11-26 15:19 ` Ingo Molnar
2017-11-24 17:23 ` [PATCH 29/43] x86/mm/kaiser: Map dynamically-allocated LDTs Ingo Molnar
2017-11-24 17:23 ` [PATCH 30/43] x86/mm/kaiser: Map espfix structures Ingo Molnar
2017-11-24 17:23 ` [PATCH 31/43] x86/mm/kaiser: Map entry stack variable Ingo Molnar
2017-11-24 17:24 ` [PATCH 32/43] x86/mm/kaiser: Map virtually-addressed performance monitoring buffers Ingo Molnar
2017-11-24 17:24 ` [PATCH 33/43] x86/mm: Move CR3 construction functions Ingo Molnar
2017-11-24 17:24 ` [PATCH 34/43] x86/mm: Remove hard-coded ASID limit checks Ingo Molnar
2017-11-24 17:24 ` [PATCH 35/43] x86/mm: Put mmu-to-h/w ASID translation in one place Ingo Molnar
2017-11-24 17:24 ` [PATCH 36/43] x86/mm/kaiser: Allow flushing for future ASID switches Ingo Molnar
2017-11-24 17:24 ` [PATCH 37/43] x86/mm/kaiser: Use PCID feature to make user and kernel switches faster Ingo Molnar
2017-11-24 17:24 ` [PATCH 38/43] x86/mm/kaiser: Disable native VSYSCALL Ingo Molnar
2017-11-24 17:24 ` [PATCH 39/43] x86/mm/kaiser: Add debugfs file to turn KAISER on/off at runtime Ingo Molnar
2017-11-24 17:24 ` [PATCH 40/43] x86/mm/kaiser: Add a function to check for KAISER being enabled Ingo Molnar
2017-11-24 17:24 ` [PATCH 41/43] x86/mm/kaiser: Un-poison PGDs at runtime Ingo Molnar
2017-11-24 17:24 ` [PATCH 42/43] x86/mm/kaiser: Allow KAISER to be enabled/disabled " Ingo Molnar
2017-11-25 19:18 ` Thomas Gleixner
2017-11-25 19:53 ` Andy Lutomirski
2017-11-25 20:05 ` Thomas Gleixner [this message]
2017-11-25 22:10 ` Andy Lutomirski
2017-11-25 22:48 ` Thomas Gleixner
2017-11-26 0:21 ` Andy Lutomirski
2017-11-26 8:11 ` Thomas Gleixner
2017-11-24 17:24 ` [PATCH 43/43] x86/mm/kaiser: Add Kconfig Ingo Molnar
2017-11-24 20:22 ` [crash] PANIC: double fault, error_code: 0x0 Ingo Molnar
2017-11-24 20:59 ` Andy Lutomirski
2017-11-24 21:49 ` Ingo Molnar
2017-11-24 21:52 ` Ingo Molnar
2017-11-24 22:09 ` Ingo Molnar
2017-11-24 22:35 ` Andy Lutomirski
2017-11-24 22:53 ` Ingo Molnar
2017-11-25 9:21 ` Ingo Molnar
2017-11-25 9:32 ` Ingo Molnar
2017-11-25 9:39 ` Ingo Molnar
2017-11-25 11:17 ` [PATCH] x86/mm/kaiser: Fix IRQ entries text section mapping Ingo Molnar
2017-11-25 16:08 ` Thomas Gleixner
2017-11-25 20:06 ` Steven Rostedt
2017-11-27 8:14 ` Peter Zijlstra
2017-11-27 8:21 ` Peter Zijlstra
2017-11-25 4:09 ` [crash] PANIC: double fault, error_code: 0x0 Dave Hansen
2017-11-25 4:15 ` Dave Hansen
-- strict thread matches above, loose matches on Subject: below --
2017-11-24 9:14 [PATCH 00/43] x86 entry-stack and Kaiser series, 2017/11/24 version Ingo Molnar
2017-11-24 9:14 ` [PATCH 42/43] x86/mm/kaiser: Allow KAISER to be enabled/disabled at runtime Ingo Molnar
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