[PATCH] KVM: arm64: vgic-debug: Exit the iterator properly w/o LPI

[PATCH] KVM: arm64: vgic-debug: Exit the iterator properly w/o LPI

[Zenghui Yu]

In case the guest doesn't have any LPI, we previously relied on the
iterator setting

	'intid = nr_spis + VGIC_NR_PRIVATE_IRQS' && 'lpi_idx = 1'

to exit the iterator. But it was broken with commit 85d3ccc8b75b ("KVM:
arm64: vgic-debug: Use an xarray mark for debug iterator") -- the intid
remains at 'nr_spis + VGIC_NR_PRIVATE_IRQS - 1', and we end up endlessly
printing the last SPI's state.

Consider that it's meaningless to search the LPI xarray and populate
lpi_idx when there is no LPI, let's just skip the process for that case.

The result is that

* If there's no LPI, we focus on the intid and exit the iterator when it
  runs out of the valid SPI range.
* Otherwise we keep the current logic and let the xarray drive the
  iterator.

Fixes: 85d3ccc8b75b ("KVM: arm64: vgic-debug: Use an xarray mark for debug iterator")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 arch/arm64/kvm/vgic/vgic-debug.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-debug.c b/arch/arm64/kvm/vgic/vgic-debug.c
index bcbc8c986b1d..bc74d06398ef 100644
--- a/arch/arm64/kvm/vgic/vgic-debug.c
+++ b/arch/arm64/kvm/vgic/vgic-debug.c
@@ -45,7 +45,8 @@ static void iter_next(struct kvm *kvm, struct vgic_state_iter *iter)
 	 * Let the xarray drive the iterator after the last SPI, as the iterator
 	 * has exhausted the sequentially-allocated INTID space.
 	 */
-	if (iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS - 1)) {
+	if (iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS - 1) &&
+	    iter->nr_lpis) {
 		if (iter->lpi_idx < iter->nr_lpis)
 			xa_find_after(&dist->lpi_xa, &iter->intid,
 				      VGIC_LPI_MAX_INTID,
@@ -112,7 +113,7 @@ static bool end_of_vgic(struct vgic_state_iter *iter)
 	return iter->dist_id > 0 &&
 		iter->vcpu_id == iter->nr_cpus &&
 		iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS) &&
-		iter->lpi_idx > iter->nr_lpis;
+		(!iter->nr_lpis || iter->lpi_idx > iter->nr_lpis);
 }
 
 static void *vgic_debug_start(struct seq_file *s, loff_t *pos)
-- 
2.33.0

Re: [PATCH] KVM: arm64: vgic-debug: Exit the iterator properly w/o LPI

[Marc Zyngier]

On Wed, 07 Aug 2024 06:20:24 +0100,
Zenghui Yu <yuzenghui@huawei.com> wrote:
> 
> In case the guest doesn't have any LPI, we previously relied on the
> iterator setting
> 
> 	'intid = nr_spis + VGIC_NR_PRIVATE_IRQS' && 'lpi_idx = 1'
> 
> to exit the iterator. But it was broken with commit 85d3ccc8b75b ("KVM:
> arm64: vgic-debug: Use an xarray mark for debug iterator") -- the intid
> remains at 'nr_spis + VGIC_NR_PRIVATE_IRQS - 1', and we end up endlessly
> printing the last SPI's state.
> 
> Consider that it's meaningless to search the LPI xarray and populate
> lpi_idx when there is no LPI, let's just skip the process for that case.
> 
> The result is that
> 
> * If there's no LPI, we focus on the intid and exit the iterator when it
>   runs out of the valid SPI range.
> * Otherwise we keep the current logic and let the xarray drive the
>   iterator.
> 
> Fixes: 85d3ccc8b75b ("KVM: arm64: vgic-debug: Use an xarray mark for debug iterator")
> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH] KVM: arm64: vgic-debug: Exit the iterator properly w/o LPI

[Oliver Upton]

On Wed, 7 Aug 2024 13:20:24 +0800, Zenghui Yu wrote:
> In case the guest doesn't have any LPI, we previously relied on the
> iterator setting
> 
> 	'intid = nr_spis + VGIC_NR_PRIVATE_IRQS' && 'lpi_idx = 1'
> 
> to exit the iterator. But it was broken with commit 85d3ccc8b75b ("KVM:
> arm64: vgic-debug: Use an xarray mark for debug iterator") -- the intid
> remains at 'nr_spis + VGIC_NR_PRIVATE_IRQS - 1', and we end up endlessly
> printing the last SPI's state.
> 
> [...]

Applied to kvmarm/fixes, thanks!

[1/1] KVM: arm64: vgic-debug: Exit the iterator properly w/o LPI
      https://git.kernel.org/kvmarm/kvmarm/c/01ab08cafece

--
Best,
Oliver