[PATCH v3 12/19] iommu/riscv: Gate identity boundary switches with live MSIs

Reject identity-boundary domain transitions while a device still has
allocated MSIs.

The RISC-V IOMMU MSI compose path can run concurrently with domain
attach and derives the MSI address rewrite policy from info->domain.
Across an identity boundary, a stale decision can turn into a wrong
addressing mode (IOVA vs PA), so require nr_msis == 0 when crossing
between paging and identity domains.

This is just a defensive guard since MSI state should be quiesced
before crossing the identity boundary anyway.

Do not gate paging <-> blocking: blocking is the fail-stop mode and
must become available immediately, even with live MSIs.

Do not gate paging -> paging: that path already uses nr_msis to
ensure new-domain MSI table readiness before install.

Signed-off-by: Andrew Jones <[email protected]>
---
 drivers/iommu/riscv/iommu.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
index 07287c0e72e7..f40db2cda417 100644
--- a/drivers/iommu/riscv/iommu.c
+++ b/drivers/iommu/riscv/iommu.c
@@ -1272,10 +1272,14 @@ static int riscv_iommu_attach_paging_domain(struct iommu_domain *iommu_domain,
 	struct riscv_iommu_domain *domain = iommu_domain_to_riscv(iommu_domain);
 	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
 	struct riscv_iommu_info *info = dev_iommu_priv_get(dev);
+	bool old_identity = old && old->type == IOMMU_DOMAIN_IDENTITY;
 	struct pt_iommu_riscv_64_hw_info pt_info;
 	u64 fsc, ta;
 	int ret;
 
+	if (old_identity && info->nr_msis)
+		return -EBUSY;
+
 	pt_iommu_riscv_64_hw_info(&domain->riscvpt, &pt_info);
 
 	if (!riscv_iommu_pt_supported(iommu, pt_info.fsc_iosatp_mode))
@@ -1394,6 +1398,10 @@ static int riscv_iommu_attach_identity_domain(struct iommu_domain *iommu_domain,
 {
 	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
 	struct riscv_iommu_info *info = dev_iommu_priv_get(dev);
+	bool old_paging = old && (old->type & __IOMMU_DOMAIN_PAGING);
+
+	if (old_paging && info->nr_msis)
+		return -EBUSY;
 
 	riscv_iommu_iodir_update(iommu, dev, RISCV_IOMMU_FSC_BARE, RISCV_IOMMU_PC_TA_V);
 	riscv_iommu_bond_unlink(rcu_access_pointer(info->domain), dev);
-- 
2.43.0