[RFC,V4,32/33] hw/intc/arm_gicv3_kvm: Pause all vCPU to ensure locking in KVM of resetting vCPU

Commit Message

Salil Mehta Oct. 9, 2024, 3:37 a.m. UTC

vCPU reset can result in device access to VGIC CPU system registers using the
`IOCTL KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS` interface. When accessing these
registers in the KVM host, it is necessary to acquire a lock on all vCPUs during
the `vgic_v3_attr_regs_access()` operation.

This operation may fail if KVM is unable to acquire the necessary locks on all
vCPUs. Therefore, to ensure proper locking of the vCPU being reset and prevent
failures, we need to *pause all vCPUs* during this operation to facilitate
successful locking within the host.

Signed-off-by: Salil Mehta <[e-mail]>
---
 hw/intc/arm_gicv3_kvm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

Patch

diff --git a/hw/intc/arm_gicv3_kvm.c b/hw/intc/arm_gicv3_kvm.c
index 3e1e97d830..bcdbf83897 100644
--- a/hw/intc/arm_gicv3_kvm.c
+++ b/hw/intc/arm_gicv3_kvm.c
@@ -714,10 +714,19 @@  static void arm_gicv3_icc_reset(CPUARMState *env, const ARMCPRegInfo *ri)
         return;
     }
 
+    /*
+     * This shall be called even when vcpu is being hotplugged or onlined and
+     * other vcpus might be running. Host kernel KVM code to handle device
+     * access of IOCTLs KVM_{GET|SET}_DEVICE_ATTR might fail due to inability to
+     * grab vcpu locks for all the vcpus. Hence, we need to pause all vcpus to
+     * facilitate locking within host.
+     */
+    pause_all_vcpus();
     /* Initialize to actual HW supported configuration */
     kvm_device_access(s->dev_fd, KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS,
                       KVM_VGIC_ATTR(ICC_CTLR_EL1, c->gicr_typer),
                       &c->icc_ctlr_el1[GICV3_NS], false, &error_abort);
+    resume_all_vcpus();
 
     c->icc_ctlr_el1[GICV3_S] = c->icc_ctlr_el1[GICV3_NS];
 }