linux-kernel - Re: [RFC patch 00/15] entry: Provide generic implementation for host and guest entry/exit work

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Date:   Fri, 20 Sep 2019 16:12:40 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-arch@...r.kernel.org, James Morse <james.morse@....com>
Subject: Re: [RFC patch 00/15] entry: Provide generic implementation for host
 and guest entry/exit work

Hi Thomas,

As a heads-up, I'm going to be away next week, and I likely won't have
the chance to look at this in detail before October.

On Thu, Sep 19, 2019 at 05:03:14PM +0200, Thomas Gleixner wrote:
> When working on a way to move out the posix cpu timer expiry out of the
> timer interrupt context, I noticed that KVM is not handling pending task
> work before entering a guest. A quick hack was to add that to the x86 KVM
> handling loop. The discussion ended with a request to make this a generic
> infrastructure possible with also moving the per arch implementations of
> the enter from and return to user space handling generic.
> 
>   https://lore.kernel.org/r/89E42BCC-47A8-458B-B06A-D6A20D20512C@amacapital.net
> 
> You asked for it, so don't complain that you have to review it :)

I never asked for this! ;)

> The series implements the syscall enter/exit and the general exit to
> userspace work handling along with the pre guest enter functionality.
> 
> The series converts x86 and ARM64. x86 is fully tested including selftests
> etc. ARM64 is only compile tested for now as my only ARM64 testbox is not
> available right now.

I've been working on converting the arm64 entry code to C for a while
now [1], gradually upstreaming the bits I can.

James has picked up some of that [2] as a prerequisite for some RAS
error handling, and I think building the arm64 bits atop of that would
be preferable. IIUC that should get posted as a series come -rc1.

Since there's immense scope for subtle breakage, I'd prefer that we do
the arm64-specific asm->C conversion before migrating arm64 to generic
code. That way us arm64 folk can ensure the asm->C conversion retains
the existing behaviour, and it'll be easier for everyone to compare the
arm64 and generic C implementations.

Thanks,
Mark.

[1] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git
[2] git://linux-arm.org/linux-jm.git -b deasm_sync_only/v1

> 
> Thanks,
> 
> 	tglx
> 
> ---
>  /Makefile                               |    3 
>  arch/Kconfig                            |    3 
>  arch/arm64/Kconfig                      |    1 
>  arch/arm64/include/asm/kvm_host.h       |    1 
>  arch/arm64/kernel/entry.S               |   18 -
>  arch/arm64/kernel/ptrace.c              |   65 ------
>  arch/arm64/kernel/signal.c              |   45 ----
>  arch/arm64/kernel/syscall.c             |   49 ----
>  arch/x86/Kconfig                        |    1 
>  arch/x86/entry/common.c                 |  265 +-------------------------
>  arch/x86/entry/entry_32.S               |   13 -
>  arch/x86/entry/entry_64.S               |   12 -
>  arch/x86/entry/entry_64_compat.S        |   21 --
>  arch/x86/include/asm/signal.h           |    1 
>  arch/x86/include/asm/thread_info.h      |    9 
>  arch/x86/kernel/signal.c                |    2 
>  arch/x86/kvm/x86.c                      |   17 -
>  b/arch/arm64/include/asm/entry-common.h |   76 +++++++
>  b/arch/x86/include/asm/entry-common.h   |  104 ++++++++++
>  b/include/linux/entry-common.h          |  324 ++++++++++++++++++++++++++++++++
>  b/kernel/entry/common.c                 |  220 +++++++++++++++++++++
>  kernel/Makefile                         |    1 
>  22 files changed, 776 insertions(+), 475 deletions(-)
> 
>