From: Thomas Gleixner <tglx@linutronix.de>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at,
michael.schwarz@iaik.tugraz.at,
richard.fellner@student.tugraz.at, luto@kernel.org,
torvalds@linux-foundation.org, keescook@google.com,
hughd@google.com, x86@kernel.org
Subject: Re: [PATCH 05/30] x86, kaiser: prepare assembly for entry/exit CR3 switching
Date: Mon, 20 Nov 2017 13:17:52 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.20.1711201226370.1734@nanos> (raw)
In-Reply-To: <20171110193107.67B798C3@viggo.jf.intel.com>
On Fri, 10 Nov 2017, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> This is largely code from Andy Lutomirski. I fixed a few bugs
> in it, and added a few SWITCH_TO_* spots.
>
> KAISER needs to switch to a different CR3 value when it enters
> the kernel and switch back when it exits. This essentially
> needs to be done before leaving assembly code.
>
> This is extra challenging because the switching context is
> tricky: the registers that can be clobbered can vary. It is also
> hard to store things on the stack because there is an established
> ABI (ptregs) or the stack is entirely unsafe to use.
Changelog nitpicking starts here
> This patch establishes a set of macros that allow changing to
s/This patch establishes/Establish/
> the user and kernel CR3 values.
>
> Interactions with SWAPGS: previous versions of the KAISER code
> relied on having per-cpu scratch space to save/restore a register
> that can be used for the CR3 MOV. The %GS register is used to
> index into our per-cpu space, so SWAPGS *had* to be done before
s/our/the/
> the CR3 switch. That scratch space is gone now, but the semantic
> that SWAPGS must be done before the CR3 MOV is retained. This is
> good to keep because it is not that hard to do and it allows us
s/us//
> to do things like add per-cpu debugging information to help us
> figure out what goes wrong sometimes.
the part after 'information' is fairy tale mode and redundant. Debugging
information says it all, right?
> What this does in the NMI code is worth pointing out. NMIs
> can interrupt *any* context and they can also be nested with
> NMIs interrupting other NMIs. The comments below
> ".Lnmi_from_kernel" explain the format of the stack during this
> situation. Changing the format of this stack is not a fun
> exercise: I tried. Instead of storing the old CR3 value on the
> stack, this patch depend on the *regular* register save/restore
> mechanism and then uses %r14 to keep CR3 during the NMI. It is
> callee-saved and will not be clobbered by the C NMI handlers that
> get called.
The comments below ".Lnmi_from_kernel" explain the format of the stack
during this situation. Changing this stack format is too complex and
risky, so the following solution has been used:
Instead of storing the old CR3 value on the stack, depend on the regular
register save/restore mechanism and use %r14 to hold CR3 during the
NMI. r14 is callee-saved and will not be clobbered by the C NMI handlers
that get called.
End of nitpicking
> +.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
> + movq %cr3, %r\scratch_reg
> + movq %r\scratch_reg, \save_reg
> + /*
> + * Is the switch bit zero? This means the address is
> + * up in real KAISER patches in a moment.
* If the switch bit is zero, CR3 points at the kernel page tables
* already.
Hmm?
> /*
> @@ -1189,6 +1201,7 @@ ENTRY(paranoid_exit)
> testl %ebx, %ebx /* swapgs needed? */
> jnz .Lparanoid_exit_no_swapgs
> TRACE_IRQS_IRETQ
> + RESTORE_CR3 %r14
You have the named macro arguments everywhere, just not here.
Other than that.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
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next prev parent reply other threads:[~2017-11-20 12:17 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-10 19:30 [PATCH 00/30] [v3] KAISER: unmap most of the kernel from userspace page tables Dave Hansen
2017-11-10 19:31 ` [PATCH 01/30] x86, mm: do not set _PAGE_USER for init_mm " Dave Hansen
2017-11-10 19:31 ` [PATCH 02/30] x86, tlb: Make CR4-based TLB flushes more robust Dave Hansen
2017-11-10 19:31 ` [PATCH 03/30] x86/mm: Document X86_CR4_PGE toggling behavior Dave Hansen
2017-11-10 19:31 ` [PATCH 04/30] x86, kaiser: disable global pages by default with KAISER Dave Hansen
2017-11-14 19:38 ` Rik van Riel
2017-11-26 14:48 ` Ingo Molnar
2017-11-27 11:37 ` Thomas Gleixner
2017-11-27 13:20 ` [PATCH v2] x86/mm/kaiser: Disable " Ingo Molnar
2017-11-27 13:23 ` Thomas Gleixner
2017-11-27 13:27 ` Ingo Molnar
2017-11-10 19:31 ` [PATCH 05/30] x86, kaiser: prepare assembly for entry/exit CR3 switching Dave Hansen
2017-11-20 12:17 ` Thomas Gleixner [this message]
2017-11-10 19:31 ` [PATCH 06/30] x86, kaiser: introduce user-mapped per-cpu areas Dave Hansen
2017-11-10 19:31 ` [PATCH 07/30] x86, kaiser: mark per-cpu data structures required for entry/exit Dave Hansen
2017-11-10 19:31 ` [PATCH 08/30] x86, kaiser: unmap kernel from userspace page tables (core patch) Dave Hansen
2017-11-20 17:21 ` Thomas Gleixner
2017-11-22 22:45 ` Dave Hansen
2017-11-22 22:50 ` Dave Hansen
2017-11-22 22:54 ` Dave Hansen
2017-11-22 23:11 ` Dave Hansen
2017-11-10 19:31 ` [PATCH 09/30] x86, kaiser: only populate shadow page tables for userspace Dave Hansen
2017-11-20 20:12 ` Thomas Gleixner
2017-11-21 7:05 ` Ingo Molnar
2017-11-21 22:09 ` Dave Hansen
2017-11-22 3:44 ` Andy Lutomirski
2017-11-22 23:30 ` Dave Hansen
2017-11-10 19:31 ` [PATCH 10/30] x86, kaiser: allow NX poison to be set in p4d/pgd Dave Hansen
2017-11-10 19:31 ` [PATCH 11/30] x86, kaiser: make sure static PGDs are 8k in size Dave Hansen
2017-11-10 19:31 ` [PATCH 12/30] x86, kaiser: map GDT into user page tables Dave Hansen
2017-11-20 20:22 ` Thomas Gleixner
2017-11-20 20:46 ` Andy Lutomirski
2017-11-20 20:55 ` Thomas Gleixner
2017-11-21 21:19 ` Dave Hansen
2017-11-21 22:46 ` Andy Lutomirski
2017-11-21 23:17 ` Dave Hansen
2017-11-21 23:32 ` Andy Lutomirski
2017-11-21 23:42 ` Dave Hansen
2017-11-22 0:17 ` Andy Lutomirski
2017-11-22 0:37 ` Dave Hansen
2017-11-21 22:12 ` Dave Hansen
2017-11-10 19:31 ` [PATCH 13/30] x86, kaiser: map dynamically-allocated LDTs Dave Hansen
2017-11-10 19:31 ` [PATCH 14/30] x86, kaiser: map espfix structures Dave Hansen
2017-11-10 19:31 ` [PATCH 15/30] x86, kaiser: map entry stack variables Dave Hansen
2017-11-10 19:31 ` [PATCH 16/30] x86, kaiser: map trace interrupt entry Dave Hansen
2017-11-10 19:31 ` [PATCH 17/30] x86, kaiser: map debug IDT tables Dave Hansen
2017-11-20 20:40 ` Thomas Gleixner
2017-11-21 22:16 ` Dave Hansen
2017-11-20 20:44 ` Andy Lutomirski
2017-11-20 20:54 ` Thomas Gleixner
2017-11-10 19:31 ` [PATCH 18/30] x86, kaiser: map virtually-addressed performance monitoring buffers Dave Hansen
2017-11-14 18:20 ` Peter Zijlstra
2017-11-14 18:28 ` Dave Hansen
2017-11-14 19:10 ` Hugh Dickins
2017-11-14 19:24 ` Andy Lutomirski
2017-11-15 9:41 ` Peter Zijlstra
2017-11-10 19:31 ` [PATCH 19/30] x86, mm: Move CR3 construction functions Dave Hansen
2017-11-10 19:31 ` [PATCH 20/30] x86, mm: remove hard-coded ASID limit checks Dave Hansen
2017-11-20 20:47 ` Thomas Gleixner
2017-11-10 19:31 ` [PATCH 21/30] x86, mm: put mmu-to-h/w ASID translation in one place Dave Hansen
2017-11-10 22:03 ` Andy Lutomirski
2017-11-10 22:09 ` Dave Hansen
2017-11-10 22:10 ` Andy Lutomirski
2017-11-10 19:31 ` [PATCH 22/30] x86, pcid, kaiser: allow flushing for future ASID switches Dave Hansen
2017-11-10 19:31 ` [PATCH 23/30] x86, kaiser: use PCID feature to make user and kernel switches faster Dave Hansen
2017-11-16 19:19 ` Andrea Arcangeli
2017-11-16 19:25 ` Dave Hansen
2017-11-10 19:31 ` [PATCH 24/30] x86, kaiser: disable native VSYSCALL Dave Hansen
2017-11-10 19:31 ` [PATCH 25/30] x86, kaiser: add debugfs file to turn KAISER on/off at runtime Dave Hansen
2017-11-10 19:31 ` [PATCH 26/30] x86, kaiser: add a function to check for KAISER being enabled Dave Hansen
2017-11-10 19:31 ` [PATCH 27/30] x86, kaiser: un-poison PGDs at runtime Dave Hansen
2017-11-10 19:31 ` [PATCH 28/30] x86, kaiser: allow KAISER to be enabled/disabled " Dave Hansen
2017-11-10 19:32 ` [PATCH 29/30] x86, kaiser: add Kconfig Dave Hansen
2017-11-10 19:32 ` [PATCH 30/30] x86, kaiser, xen: Dynamically disable KAISER when running under Xen PV Dave Hansen
2017-11-20 16:02 ` [PATCH 00/30] [v3] KAISER: unmap most of the kernel from userspace page tables Juerg Haefliger
-- strict thread matches above, loose matches on Subject: below --
2017-11-08 19:46 [PATCH 00/30] [v2] " Dave Hansen
2017-11-08 19:46 ` [PATCH 05/30] x86, kaiser: prepare assembly for entry/exit CR3 switching Dave Hansen
2017-11-09 13:20 ` Borislav Petkov
2017-11-09 15:34 ` Dave Hansen
2017-11-09 15:59 ` Borislav Petkov
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