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KVM: arm64: Use standard seq_file iterator for vgic-debug debugfs

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The current implementation uses `vgic_state_iter` in `struct
vgic_dist` to track the sequence position. This effectively makes the
iterator shared across all open file descriptors for the VM.

This approach has significant drawbacks:
- It enforces mutual exclusion, preventing concurrent reads of the
  debugfs file (returning -EBUSY).
- It relies on storing transient iterator state in the long-lived
  VM structure (`vgic_dist`).

Refactor the implementation to use the standard `seq_file` iterator.
Instead of storing state in `kvm_arch`, rely on the `pos` argument
passed to the `start` and `next` callbacks, which tracks the logical
index specific to the file descriptor.

This change enables concurrent access and eliminates the
`vgic_state_iter` field from `struct vgic_dist`.

Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260202085721.3954942-4-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Fuad Tabba 2026-02-02 08:57:21 +00:00 • committed by Marc Zyngier
parent 5ab2496970
commit fb21cb0856
2 changed files with 12 additions and 31 deletions
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40
arch/arm64/kvm/vgic/vgic-debug.c
View file

@ -104,58 +104,42 @@ static void *vgic_debug_start(struct seq_file *s, loff_t *pos)
struct kvm *kvm = s->private;
struct vgic_state_iter *iter;
mutex_lock(&kvm->arch.config_lock);
iter = kvm->arch.vgic.iter;
if (iter) {
iter = ERR_PTR(-EBUSY);
goto out;
}
iter = kmalloc(sizeof(*iter), GFP_KERNEL);
if (!iter) {
iter = ERR_PTR(-ENOMEM);
goto out;
}
if (!iter)
return ERR_PTR(-ENOMEM);
iter_init(kvm, iter, *pos);
kvm->arch.vgic.iter = iter;
if (end_of_vgic(iter))
if (end_of_vgic(iter)) {
kfree(iter);
iter = NULL;
out:
mutex_unlock(&kvm->arch.config_lock);
}
return iter;
}
static void *vgic_debug_next(struct seq_file *s, void *v, loff_t *pos)
{
struct kvm *kvm = s->private;
struct vgic_state_iter *iter = kvm->arch.vgic.iter;
struct vgic_state_iter *iter = v;
++*pos;
iter_next(kvm, iter);
if (end_of_vgic(iter))
if (end_of_vgic(iter)) {
kfree(iter);
iter = NULL;
}
return iter;
}
static void vgic_debug_stop(struct seq_file *s, void *v)
{
struct kvm *kvm = s->private;
struct vgic_state_iter *iter;
struct vgic_state_iter *iter = v;
/*
* If the seq file wasn't properly opened, there's nothing to clearn
* up.
*/
if (IS_ERR(v))
if (IS_ERR_OR_NULL(v))
return;
mutex_lock(&kvm->arch.config_lock);
iter = kvm->arch.vgic.iter;
kfree(iter);
kvm->arch.vgic.iter = NULL;
mutex_unlock(&kvm->arch.config_lock);
}
static void print_dist_state(struct seq_file *s, struct vgic_dist *dist,

3
include/kvm/arm_vgic.h
View file

@ -302,9 +302,6 @@ struct vgic_dist {
struct xarray lpi_xa;
/* used by vgic-debug */
struct vgic_state_iter *iter;
/*
* GICv4 ITS per-VM data, containing the IRQ domain, the VPE
* array, the property table pointer as well as allocation