On 2021-01-04 15:47, Qian Cai wrote:
On Thu, 2020-12-10 at 08:30 +0000, Marc Zyngier wrote:
We reset the guest's view of PMCR_EL0 unconditionally, based on
the host's view of this register. It is however legal for an
imnplementation not to provide any PMU, resulting in an UNDEF.
The obvious fix is to skip the reset of this shadow register
when no PMU is available, sidestepping the issue entirely.
If no PMU is available, the guest is not able to request
a virtual PMU anyway, so not doing nothing is the right thing
to do!
It is unlikely that this bug can hit any HW implementation
though, as they all provide a PMU. It has been found using nested
virt with the host KVM not implementing the PMU itself.
Fixes: ab9468340d2bc ("arm64: KVM: Add access handler for PMCR
register")
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Reverting this commit on the top of today's linux-next fixed a qemu-kvm
coredump
issue on TX2 while starting a guest.
- host kernel .config:
https://cailca.coding.net/public/linux/mm/git/files/master/arm64.config
# /usr/libexec/qemu-kvm -name ubuntu-20.04-server-cloudimg -cpu host
-smp 2 -m 2g
-drive
if=none,format=qcow2,file=./ubuntu-20.04-server-cloudimg.qcow2,id=hd
-device virtio-scsi -device scsi-hd,drive=hd -cdrom
./ubuntu-20.04-server-cloudimg.iso
-bios /usr/share/AAVMF/AAVMF_CODE.fd -M gic-version=host -nographic
-nic user,model=virtio,hostfwd=tcp::2222-:22
qemu-kvm: /builddir/build/BUILD/qemu-4.2.0/target/arm/helper.c:1812:
pmevcntr_rawwrite: Assertion `counter < pmu_num_counters(env)' failed.
You don't have KVM_ARM_PMU selected in your config, so QEMU cannot
access the PMU registers, and no counters are exposed.
M.
--
Jazz is not dead. It just smells funny...
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