[PATCH v2 0/2] KVM: arm64: vgic-v4: Don't allocate vPEs that a VM can't use

[Fuad Tabba <fuad.tabba@linux.dev>]

Hi folks,

Changes since v1 [1]:
  - Gate vgic_v4_init() on vgic_supports_vpes(), split out of
    vgic_supports_direct_msis(), instead of open coding the nASSGIcap
    check. (Oliver)
  - Use vgic_is_v3() for the GICv2 check, in vgic_supports_vpes(). (Oliver)

Two fixes for vgic_its_create() allocating vPEs for a VM that never
uses them. Nothing frees them when the VM is destroyed, and each
doorbell handler stays registered with a freed vCPU.

The first is for a GICv2 VM, which KVM can run on a GICv4.0 host whose
CPU interface supports legacy operation. The second is for a GICv3 VM
whose VMM cleared nASSGIcap on a GICv4.1 host with vSGIs.

The second patch also moves the first one's GICv3 check into
vgic_supports_vpes(). I kept them separate because the first can be
backported on its own to stable kernels that predate nASSGIcap, which
is also why it open codes the check: vgic_is_v3() only exists since
7.1. The end state is what Oliver asked for.

Tested on AEM FVP, with has-gicv4.1=0 for the GICv2 case and =1 for the
other. With my reproducer (clear nASSGIcap for the second case,
initialise the vgic, create an ITS, destroy the VM), the kernel without
the fix leaves four "vcpu" doorbells in /proc/interrupts in each case,
and the fixed one doesn't leave any.

Based on Linux 7.3-rc3 (fd73f4a665989).

Cheers,
/fuad

[1] https://lore.kernel.org/all/20261026152639.3926498-1-fuad.tabba@linux.dev/

Fuad Tabba (2):
  KVM: arm64: vgic-v4: Don't allocate vPEs for a GICv2 VM
  KVM: arm64: vgic-v4: Don't allocate vPEs when userspace clears
    nASSGIcap

 arch/arm64/kvm/vgic/vgic-mmio-v3.c | 9 +++++++--
 arch/arm64/kvm/vgic/vgic-v4.c      | 2 +-
 arch/arm64/kvm/vgic/vgic.h         | 1 +
 3 files changed, 9 insertions(+), 3 deletions(-)


base-commit: fd73f4a6659897191fa0d40695fe370925dd3780
-- 
2.47.3