linux-kernel - Re: [patch 00/10] x86/entry: Consolidation

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Message-ID: <51331157-eef1-f064-f098-faae7b2d25d7@oracle.com>
Date:   Thu, 27 Feb 2020 12:01:22 +0100
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [patch 00/10] x86/entry: Consolidation - Part I


On 2/25/20 10:36 PM, Thomas Gleixner wrote:
> Hi!
> 
> This is the first batch of a 73 patches series which consolidates the x86
> entry code.
> 
> This work started off as a trivial 5 patches series moving the heavy
> lifting of POSIX CPU timers out of interrupt context into thread/process
> context. This discovered that KVM is lacking to handle pending work items
> before entering guest mode and added the handling to the x86 KVM
> code. Review requested to make this a generic infrastructure.
> 
> The next series grew to 25 patches implementing the generic infrastructure,
> converting x86 (and as a POC ARM64) over, but it turned out that this was
> slightly incomplete and still had some entanglement with the rest of the
> x86 entry code as some of that functionality is shared between syscall and
> interrupt entry/exit. And it also unearthed the nastyness of IOPL which got
> already addressed in mainline.
> 
> This series addresses these issues in order to prepare for making the entry
> from userspace and exit to userspace (and it's counterpart enter guest) a
> generic infrastructure in order to restrict the necessary ASM work to the
> bare minimum.
> 
> The series is split into 5 parts:
> 
>      - General cleanups and bugfixes
> 
>      - Consolidation of the syscall entry/exit code
> 
>      - Autogenerate simple exception/trap code and reduce the difference
>        between 32 and 64 bit
> 
>      - Autogenerate complex exception/trap code and provide different entry
>        points for #DB and #MC exceptions which allows to address the
>        recently discovered RCU vs. world issues in a more structured way
> 
>      - Convert the device interrupt entry code to use the same mechanism as
>        exceptions and traps and finally convert the system vectors over as
>        well. The last step after all those cleanups is to move the return
>        from exception/interrupt logic (user mode work, kernel preemption)
>        completely from ASM into C-code, so the ASM code just has to take
>        care about returning from the exception, which is horrible and
>        convoluted enough already.
> 
> At the end the x86 entry code is ready to move the syscall parts out into
> generic code and finally tackle the initial problem which started all of
> this.
> 
> The complete series is available from git:
> 
>     git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git x86/entry
> 
> which contains all 73 patches. The individual parts are tagged, so this
> part can be retrieved via:
> 
>     git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git entry-v1-part1
> 
> Thanks,
> 
> 	tglx
> 
> 8<---------------
>   entry/entry_32.S          |   19 +++++++------------
>   include/asm/irq.h         |    2 +-
>   include/asm/mce.h         |    3 ---
>   include/asm/traps.h       |   17 +++++++----------
>   kernel/cpu/mce/core.c     |   12 ++++++++++--
>   kernel/cpu/mce/internal.h |    3 +++
>   kernel/irq.c              |    3 +--
>   kernel/traps.c            |   41 ++++++++++++++++++++++++++++++++++-------
>   8 files changed, 63 insertions(+), 37 deletions(-)
> 

For part I:

Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>

for all patches. I had a slight concern about patch 08 and propagating a different
error_code, but I agree with your argument that it is limited to 32-bit process and
now matches with the 64-bit behavior.

alex.