[PATCH 1/2] accel: tcg: Allow forcing a store fault on read ops

[Alistair Francis]

From: Alistair Francis <alistair.francis@wdc.com>

When performing atomic operations TCG will do a read operation then a
write operation. This results in a MMU_DATA_LOAD fault if the address is
invalid.

For some platforms (such as RISC-V) we should produce a store fault if
an atomic operation fails. This patch adds a new MemOp (MO_WRITE_FAULT)
that allows us to indicate that the operation should produce a
MMU_DATA_STORE access type if the operation faults.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 include/exec/memop.h |  2 ++
 accel/tcg/cputlb.c   | 11 +++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/exec/memop.h b/include/exec/memop.h
index 2a885f3917..93ae1b6a2e 100644
--- a/include/exec/memop.h
+++ b/include/exec/memop.h
@@ -81,6 +81,8 @@ typedef enum MemOp {
     MO_ALIGN_32 = 5 << MO_ASHIFT,
     MO_ALIGN_64 = 6 << MO_ASHIFT,
 
+    MO_WRITE_FAULT = 0x100,
+
     /* Combinations of the above, for ease of use.  */
     MO_UB    = MO_8,
     MO_UW    = MO_16,
diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
index 5e0d0eebc3..320555d5e9 100644
--- a/accel/tcg/cputlb.c
+++ b/accel/tcg/cputlb.c
@@ -1362,8 +1362,15 @@ static uint64_t io_readx(CPUArchState *env, 
CPUIOTLBEntry *iotlbentry,
             section->offset_within_address_space -
             section->offset_within_region;
 
-        cpu_transaction_failed(cpu, physaddr, addr, memop_size(op), 
access_type,
-                               mmu_idx, iotlbentry->attrs, r, retaddr);
+        if (op & MO_WRITE_FAULT) {
+            cpu_transaction_failed(cpu, physaddr, addr, memop_size(op),
+                                   MMU_DATA_STORE, mmu_idx, iotlbentry->attrs,
+                                   r, retaddr);
+        } else {
+            cpu_transaction_failed(cpu, physaddr, addr, memop_size(op),
+                                   access_type, mmu_idx, iotlbentry->attrs,
+                                   r, retaddr);
+        }
     }
     if (locked) {
         qemu_mutex_unlock_iothread();
-- 
2.31.1