[PATCH v7 26/28] iommu/tegra241-cmdqv: Do not statically map LVCMDQs

Nicolin Chen
2025-06-26T20:35:40Z

To simplify the mappings from global VCMDQs to VINTFs' LVCMDQs, the design
chose to do static allocations and mappings in the global reset function.

However, with the user-owned VINTF support, it exposes a security concern:
if user space VM only wants one LVCMDQ for a VINTF, statically mapping two
or more LVCMDQs creates a hidden VCMDQ that user space could DoS attack by
writing random stuff to overwhelm the kernel with unhandleable IRQs.

Thus, to support the user-owned VINTF feature, a LVCMDQ mapping has to be
done dynamically.

HW allows pre-assigning global VCMDQs in the CMDQ_ALLOC registers, without
finalizing the mappings by keeping CMDQV_CMDQ_ALLOCATED=0. So, add a pair
of map/unmap helper that simply sets/clears that bit.

For kernel-owned VINTF0, move LVCMDQ mappings to tegra241_vintf_hw_init(),
and the unmappings to tegra241_vintf_hw_deinit().

For user-owned VINTFs that will be added, the mappings/unmappings will be
on demand upon an LVCMDQ allocation from the user space.

However, the dynamic LVCMDQ mapping/unmapping can complicate the timing of
calling tegra241_vcmdq_hw_init/deinit(), which write LVCMDQ address space,
i.e. requiring LVCMDQ to be mapped. Highlight that with a note to the top
of either of them.

Acked-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
.../iommu/arm/arm-smmu-v3/tegra241-cmdqv.c | 37 +++++++++++++++++--
1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
index 8d418c131b1b..869c90b660c1 100644
--- a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
+++ b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
@@ -351,6 +351,7 @@ tegra241_cmdqv_get_cmdq(struct arm_smmu_device *smmu,

/* HW Reset Functions */

+/* This function is for LVCMDQ, so @vcmdq must not be unmapped yet */
static void tegra241_vcmdq_hw_deinit(struct tegra241_vcmdq *vcmdq)
{
char header[64], *h = lvcmdq_error_header(vcmdq, header, 64);
@@ -379,6 +380,7 @@ static void tegra241_vcmdq_hw_deinit(struct tegra241_vcmdq *vcmdq)
dev_dbg(vcmdq->cmdqv->dev, "%sdeinited\n", h);
}

+/* This function is for LVCMDQ, so @vcmdq must be mapped prior */
static int tegra241_vcmdq_hw_init(struct tegra241_vcmdq *vcmdq)
{
char header[64], *h = lvcmdq_error_header(vcmdq, header, 64);
@@ -404,16 +406,42 @@ static int tegra241_vcmdq_hw_init(struct tegra241_vcmdq *vcmdq)
return 0;
}

+/* Unmap a global VCMDQ from the pre-assigned LVCMDQ */
+static void tegra241_vcmdq_unmap_lvcmdq(struct tegra241_vcmdq *vcmdq)
+{
+ u32 regval = readl(REG_CMDQV(vcmdq->cmdqv, CMDQ_ALLOC(vcmdq->idx)));
+ char header[64], *h = lvcmdq_error_header(vcmdq, header, 64);
+
+ writel(regval & ~CMDQV_CMDQ_ALLOCATED,
+ REG_CMDQV(vcmdq->cmdqv, CMDQ_ALLOC(vcmdq->idx)));
+ dev_dbg(vcmdq->cmdqv->dev, "%sunmapped\n", h);
+}
+
static void tegra241_vintf_hw_deinit(struct tegra241_vintf *vintf)
{
- u16 lidx;
+ u16 lidx = vintf->cmdqv->num_lvcmdqs_per_vintf;

- for (lidx = 0; lidx < vintf->cmdqv->num_lvcmdqs_per_vintf; lidx++)
- if (vintf->lvcmdqs && vintf->lvcmdqs[lidx])
+ /* HW requires to unmap LVCMDQs in descending order */
+ while (lidx--) {
+ if (vintf->lvcmdqs && vintf->lvcmdqs[lidx]) {
tegra241_vcmdq_hw_deinit(vintf->lvcmdqs[lidx]);
+ tegra241_vcmdq_unmap_lvcmdq(vintf->lvcmdqs[lidx]);
+ }
+ }
vintf_write_config(vintf, 0);
}

+/* Map a global VCMDQ to the pre-assigned LVCMDQ */
+static void tegra241_vcmdq_map_lvcmdq(struct tegra241_vcmdq *vcmdq)
+{
+ u32 regval = readl(REG_CMDQV(vcmdq->cmdqv, CMDQ_ALLOC(vcmdq->idx)));
+ char header[64], *h = lvcmdq_error_header(vcmdq, header, 64);
+
+ writel(regval | CMDQV_CMDQ_ALLOCATED,
+ REG_CMDQV(vcmdq->cmdqv, CMDQ_ALLOC(vcmdq->idx)));
+ dev_dbg(vcmdq->cmdqv->dev, "%smapped\n", h);
+}
+
static int tegra241_vintf_hw_init(struct tegra241_vintf *vintf, bool hyp_own)
{
u32 regval;
@@ -441,8 +469,10 @@ static int tegra241_vintf_hw_init(struct tegra241_vintf *vintf, bool hyp_own)
*/
vintf->hyp_own = !!(VINTF_HYP_OWN & readl(REG_VINTF(vintf, CONFIG)));

+ /* HW requires to map LVCMDQs in ascending order */
for (lidx = 0; lidx < vintf->cmdqv->num_lvcmdqs_per_vintf; lidx++) {
if (vintf->lvcmdqs && vintf->lvcmdqs[lidx]) {
+ tegra241_vcmdq_map_lvcmdq(vintf->lvcmdqs[lidx]);
ret = tegra241_vcmdq_hw_init(vintf->lvcmdqs[lidx]);
if (ret) {
tegra241_vintf_hw_deinit(vintf);
@@ -476,7 +506,6 @@ static int tegra241_cmdqv_hw_reset(struct arm_smmu_device *smmu)
for (lidx = 0; lidx < cmdqv->num_lvcmdqs_per_vintf; lidx++) {
regval = FIELD_PREP(CMDQV_CMDQ_ALLOC_VINTF, idx);
regval |= FIELD_PREP(CMDQV_CMDQ_ALLOC_LVCMDQ, lidx);
- regval |= CMDQV_CMDQ_ALLOCATED;
writel_relaxed(regval,
REG_CMDQV(cmdqv, CMDQ_ALLOC(qidx++)));
}
--
2.43.0