linux-kernel - Re: [PATCH 0/2] KVM: s390: Fix latent guest entry/exit bugs

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Message-ID: <447aafca-124a-45fc-85b2-8a653466fa34@linux.ibm.com>
Date: Wed, 9 Jul 2025 11:22:27 +0200
From: Janosch Frank <frankja@...ux.ibm.com>
To: Andrew Donnellan <ajd@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org
Cc: Mark Rutland <mark.rutland@....com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Heiko Carstens
 <hca@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Sven Schnelle
 <svens@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andy Lutomirski
 <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/2] KVM: s390: Fix latent guest entry/exit bugs

On 7/8/25 11:27 AM, Andrew Donnellan wrote:
> In [0], the guest_{enter,exit}_irqoff() helpers were deprecated, in favour
> of guest_timing_{enter,exit}_irqoff() and
> guest_context_{enter,exit}_irqoff(). This was to fix a number of latent
> guest entry/exit bugs, relating to the enabling of interrupts during an
> RCU extended quiescent state, instrumentation code, and correct handling
> of lockdep and tracing.
> 
> However, while arm64, mips, riscv and x86 have been migrated to the new
> helpers, s390 hasn't been. There was an initial attempt at [1] to do this,
> but that didn't work for reasons discussed at [2].
> 
> Since then, Claudio Imbrenda has reworked much of the interrupt handling.
> Moving interrupt handling into vcpu_post_run() avoids the issues in [2],
> so we can now move to the new helpers.
> 
> I've rebased Mark's patches from [1]. kvm-unit-tests, the kvm selftests,
> and IBM's internal test suites pass under debug_defconfig.
> 
> These patches do introduce some overhead - in my testing, a few of the
> tests in the kvm-unit-tests exittime test suite appear 6-11% slower, but
> some noticeable overhead may be unavoidable (we introduce a new function
> call and the irq entry/exit paths change a bit).
> 

This series has been part of our CI runs for some while and hasn't 
caused issues.

Series:
Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>