[PATCH v4 21/23] iommu/tegra241-cmdqv: Do not statically map LVCMDQs

[Nicolin Chen <nicolinc@nvidia.com>]

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.

Delay the LVCMDQ mappings to tegra241_vintf_hw_init(), and the unmappings
to tegra241_vintf_hw_deinit().

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>
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