linux-kernel - [PATCH 0/3] KVM: s390: Use generic VIRT_XFER_TO_GUEST

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Message-Id: <20251125-s390-kvm-xfer-to-guest-work-v1-0-091281a34611@linux.ibm.com>
Date: Tue, 25 Nov 2025 18:45:51 +1100
From: Andrew Donnellan <ajd@...ux.ibm.com>
To: kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>
Cc: Nicholas Miehlbradt <nicholas@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        David Hildenbrand <david@...nel.org>
Subject: [PATCH 0/3] KVM: s390: Use generic VIRT_XFER_TO_GUEST_WORK entry
 helpers

This series enables VIRT_XFER_TO_GUEST_WORK on s390.

This requires:

  1) adding a signal_exits stats counter, which is used by
     kvm_handle_signal_exit()
  2) moving the point where interrupts are enabled and disabled in the
     guest entry path, so that interrupts aren't enabled until after the
     __TI_sie flag is set
  3) enabling VIRT_XFER_TO_GUEST_WORK and adding the appropriate calls to
     check for and handle outstanding work in __vcpu_run() and the VSIE
     path.

With this series applied, the kvm-unit-tests suite passes on both the host
and an L1 guest with nested KVM enabled, and benchmarks done using the
exittime tests from kvm-unit-tests show that the impact on entry path
performance is generally small enough to be noise (in my tests, around
+/-3%, running directly in an LPAR and in a L1 KVM guest).

Thanks to Heiko for feedback and guidance on this.

Signed-off-by: Andrew Donnellan <ajd@...ux.ibm.com>
---
Andrew Donnellan (2):
      KVM: s390: Add signal_exits counter
      KVM: s390: Use generic VIRT_XFER_TO_GUEST_WORK functions

Heiko Carstens (1):
      KVM: s390: Enable and disable interrupts in entry code

 arch/s390/include/asm/kvm_host.h   |  1 +
 arch/s390/include/asm/stacktrace.h |  1 +
 arch/s390/kernel/asm-offsets.c     |  1 +
 arch/s390/kernel/entry.S           |  2 ++
 arch/s390/kvm/Kconfig              |  1 +
 arch/s390/kvm/kvm-s390.c           | 34 +++++++++++++++++++++-------------
 arch/s390/kvm/vsie.c               | 17 ++++++++++++-----
 7 files changed, 39 insertions(+), 18 deletions(-)
---
base-commit: ac3fd01e4c1efce8f2c054cdeb2ddd2fc0fb150d
change-id: 20251105-s390-kvm-xfer-to-guest-work-3eaba6c0ea04


--
Andrew Donnellan    OzLabs, ADL Canberra
ajd@...ux.ibm.com   IBM Australia Limited