# git rev-parse -q --verify 74f02dbcaa622a8fa4171dcc6e12f86d2cb007d0^{commit}
74f02dbcaa622a8fa4171dcc6e12f86d2cb007d0
already have revision, skipping fetch
# git checkout -q -f -B kisskb 74f02dbcaa622a8fa4171dcc6e12f86d2cb007d0
# git clean -qxdf
# < git log -1
# commit 74f02dbcaa622a8fa4171dcc6e12f86d2cb007d0
# Author: Gautam Menghani <gautam@linux.ibm.com>
# Date:   Mon Oct 28 14:34:09 2024 +0530
# 
#     KVM: PPC: Book3S HV: Mask off LPCR_MER for a vCPU before running it to avoid spurious interrupts
#     
#     Running a L2 vCPU (see [1] for terminology) with LPCR_MER bit set and no
#     pending interrupts results in that L2 vCPU getting an infinite flood of
#     spurious interrupts. The 'if check' in kvmhv_run_single_vcpu() sets the
#     LPCR_MER bit if there are pending interrupts.
#     
#     The spurious flood problem can be observed in 2 cases:
#     1. Crashing the guest while interrupt heavy workload is running
#       a. Start a L2 guest and run an interrupt heavy workload (eg: ipistorm)
#       b. While the workload is running, crash the guest (make sure kdump
#          is configured)
#       c. Any one of the vCPUs of the guest will start getting an infinite
#          flood of spurious interrupts.
#     
#     2. Running LTP stress tests in multiple guests at the same time
#        a. Start 4 L2 guests.
#        b. Start running LTP stress tests on all 4 guests at same time.
#        c. In some time, any one/more of the vCPUs of any of the guests will
#           start getting an infinite flood of spurious interrupts.
#     
#     The root cause of both the above issues is the same:
#     1. A NMI is sent to a running vCPU that has LPCR_MER bit set.
#     2. In the NMI path, all registers are refreshed, i.e, H_GUEST_GET_STATE
#        is called for all the registers.
#     3. When H_GUEST_GET_STATE is called for LPCR, the vcpu->arch.vcore->lpcr
#        of that vCPU at L1 level gets updated with LPCR_MER set to 1, and this
#        new value is always used whenever that vCPU runs, regardless of whether
#        there was a pending interrupt.
#     4. Since LPCR_MER is set, the vCPU in L2 always jumps to the external
#        interrupt handler, and this cycle never ends.
#     
#     Fix the spurious flood by masking off the LPCR_MER bit before running a
#     L2 vCPU to ensure that it is not set if there are no pending interrupts.
#     
#     [1] Terminology:
#     1. L0 : PAPR hypervisor running in HV mode
#     2. L1 : Linux guest (logical partition) running on top of L0
#     3. L2 : KVM guest running on top of L1
#     
#     Fixes: ec0f6639fa88 ("KVM: PPC: Book3S HV nestedv2: Ensure LPCR_MER bit is passed to the L0")
#     Cc: stable@vger.kernel.org # v6.8+
#     Signed-off-by: Gautam Menghani <gautam@linux.ibm.com>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://patch.msgid.link/20241028090411.34625-1-gautam@linux.ibm.com
# < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 74f02dbcaa622a8fa4171dcc6e12f86d2cb007d0
# make -s -j 40 ARCH=powerpc O=/kisskb/build/powerpc-fixes_skiroot_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  skiroot_defconfig
# < make -s -j 40 ARCH=powerpc O=/kisskb/build/powerpc-fixes_skiroot_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 40 ARCH=powerpc O=/kisskb/build/powerpc-fixes_skiroot_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
# make -s -j 40 ARCH=powerpc O=/kisskb/build/powerpc-fixes_skiroot_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_skiroot_defconfig_powerpc-gcc5
# Build took: 0:01:02.683926