KVM_CAP_MAX_VCPUS always return the maximum possible number of
VCPUs, irrespective of the selected interrupt controller. This
is pretty misleading for userspace that selects a GICv2 on a GICv3
system that supports v2 compat: It always gets a maximum of 512
VCPUs, even if the effective limit is 8. The 9th VCPU will fail
to be created, which is unexpected as far as userspace is concerned.
Fortunately, we already have the right information stashed in the
kvm structure, and we can return it as requested.
Reported-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Alexandru Elisei <alexandru.elisei@arm.com>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20200427141507.284985-1-maz@kernel.org
stage2_unmap_vm() was introduced to unmap user RAM region in the stage2
page table to make the caches coherent. E.g., a guest reboot with stage1
MMU disabled will access memory using non-cacheable attributes. If the
RAM and caches are not coherent at this stage, some evicted dirty cache
line may go and corrupt guest data in RAM.
Since ARMv8.4, S2FWB feature is mandatory and KVM will take advantage
of it to configure the stage2 page table and the attributes of memory
access. So we ensure that guests always access memory using cacheable
attributes and thus, the caches always be coherent.
So on CPUs that support S2FWB, we can safely reset the vcpu without a
heavy stage2 unmapping.
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200415072835.1164-1-yuzenghui@huawei.com
