hw/riscv: riscv-iommu: Don't look up DDT cache in Off and Bare modes

According to the RISC-V IOMMU specification:

* When ddtp.iommu_mode is set to Off, there is no DDT look-up, and an "All
  inbound transactions disallowed" fault (cause = 256) is reported for any
  inbound transaction.

* When ddtp.iommu_mode is set to Bare, there is no DDT look-up, and the
  translated address is the same as the IOVA, unless the transaction type
  is disallowed (cause = 260).

In the current implementation, the DDT cache is incorrectly looked up
even when ddtp.iommu_mode is set to Off or Bare. This may result in
unintended cache hits.

Therefore, the DDT cache must not be looked up when ddtp.iommu_mode is
set to Off or Bare. For other modes, software is required to issue cache
invalidation commands before any inbound transactions.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Jim Shu <jim.shu@sifive.com>
Message-ID: <20251028085032.2053569-1-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

diff --git a/hw/riscv/riscv-iommu.c b/hw/riscv/riscv-iommu.c
index 01730109c7769fbe94b97933ebece9b6a317cc13..b46b337375aa3470f101be40386332fc68c3e765 100644 (file)
--- a/hw/riscv/riscv-iommu.c
+++ b/hw/riscv/riscv-iommu.c
@@ -1292,13 +1292,18 @@ static RISCVIOMMUContext *riscv_iommu_ctx(RISCVIOMMUState *s,
         .devid = devid,
         .process_id = process_id,
     };
+    unsigned mode = get_field(s->ddtp, RISCV_IOMMU_DDTP_MODE);
 
     ctx_cache = g_hash_table_ref(s->ctx_cache);
-    ctx = g_hash_table_lookup(ctx_cache, &key);
 
-    if (ctx && (ctx->tc & RISCV_IOMMU_DC_TC_V)) {
-        *ref = ctx_cache;
-        return ctx;
+    if (mode != RISCV_IOMMU_DDTP_MODE_OFF &&
+        mode != RISCV_IOMMU_DDTP_MODE_BARE) {
+        ctx = g_hash_table_lookup(ctx_cache, &key);
+
+        if (ctx && (ctx->tc & RISCV_IOMMU_DC_TC_V)) {
+            *ref = ctx_cache;
+            return ctx;
+        }
     }
 
     ctx = g_new0(RISCVIOMMUContext, 1);