[Qemu-devel] [PATCH 3/8] cputlb: Support generating CPU exceptions on memory transaction failures

[Peter Maydell <peter.maydell@linaro.org>]

Call the new cpu_transaction_failed() hook at the places where
CPU generated code interacts with the memory system:
 io_readx()
 io_writex()
 get_page_addr_code()

Any access from C code (eg via cpu_physical_memory_rw(),
address_space_rw(), ld/st_*_phys()) will *not* trigger CPU exceptions
via cpu_transaction_failed().  Handling for transactions failures for
this kind of call should be done by using a function which returns a
MemTxResult and treating the failure case appropriately in the
calling code.

In an ideal world we would not generate CPU exceptions for
instruction fetch failures in get_page_addr_code() but instead wait
until the code translation process tried a load and it failed;
however that change would require too great a restructuring and
redesign to attempt at this point.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 softmmu_template.h |  4 ++--
 accel/tcg/cputlb.c | 32 ++++++++++++++++++++++++++++++--
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/softmmu_template.h b/softmmu_template.h
index 4a2b665..d756329 100644
--- a/softmmu_template.h
+++ b/softmmu_template.h
@@ -101,7 +101,7 @@ static inline DATA_TYPE glue(io_read, SUFFIX)(CPUArchState *env,
                                               uintptr_t retaddr)
 {
     CPUIOTLBEntry *iotlbentry = &env->iotlb[mmu_idx][index];
-    return io_readx(env, iotlbentry, addr, retaddr, DATA_SIZE);
+    return io_readx(env, iotlbentry, mmu_idx, addr, retaddr, DATA_SIZE);
 }
 #endif
 
@@ -262,7 +262,7 @@ static inline void glue(io_write, SUFFIX)(CPUArchState *env,
                                           uintptr_t retaddr)
 {
     CPUIOTLBEntry *iotlbentry = &env->iotlb[mmu_idx][index];
-    return io_writex(env, iotlbentry, val, addr, retaddr, DATA_SIZE);
+    return io_writex(env, iotlbentry, mmu_idx, val, addr, retaddr, DATA_SIZE);
 }
 
 void helper_le_st_name(CPUArchState *env, target_ulong addr, DATA_TYPE val,
diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
index 85635ae..e72415a 100644
--- a/accel/tcg/cputlb.c
+++ b/accel/tcg/cputlb.c
@@ -747,6 +747,7 @@ static inline ram_addr_t qemu_ram_addr_from_host_nofail(void *ptr)
 }
 
 static uint64_t io_readx(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
+                         int mmu_idx,
                          target_ulong addr, uintptr_t retaddr, int size)
 {
     CPUState *cpu = ENV_GET_CPU(env);
@@ -754,6 +755,7 @@ static uint64_t io_readx(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
     MemoryRegion *mr = iotlb_to_region(cpu, physaddr, iotlbentry->attrs);
     uint64_t val;
     bool locked = false;
+    MemTxResult r;
 
     physaddr = (physaddr & TARGET_PAGE_MASK) + addr;
     cpu->mem_io_pc = retaddr;
@@ -767,7 +769,12 @@ static uint64_t io_readx(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
         qemu_mutex_lock_iothread();
         locked = true;
     }
-    memory_region_dispatch_read(mr, physaddr, &val, size, iotlbentry->attrs);
+    r = memory_region_dispatch_read(mr, physaddr,
+                                    &val, size, iotlbentry->attrs);
+    if (r != MEMTX_OK) {
+        cpu_transaction_failed(cpu, physaddr, addr, size, MMU_DATA_LOAD,
+                               mmu_idx, iotlbentry->attrs, r, retaddr);
+    }
     if (locked) {
         qemu_mutex_unlock_iothread();
     }
@@ -776,6 +783,7 @@ static uint64_t io_readx(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
 }
 
 static void io_writex(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
+                      int mmu_idx,
                       uint64_t val, target_ulong addr,
                       uintptr_t retaddr, int size)
 {
@@ -783,6 +791,7 @@ static void io_writex(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
     hwaddr physaddr = iotlbentry->addr;
     MemoryRegion *mr = iotlb_to_region(cpu, physaddr, iotlbentry->attrs);
     bool locked = false;
+    MemTxResult r;
 
     physaddr = (physaddr & TARGET_PAGE_MASK) + addr;
     if (mr != &io_mem_rom && mr != &io_mem_notdirty && !cpu->can_do_io) {
@@ -795,7 +804,12 @@ static void io_writex(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
         qemu_mutex_lock_iothread();
         locked = true;
     }
-    memory_region_dispatch_write(mr, physaddr, val, size, iotlbentry->attrs);
+    r = memory_region_dispatch_write(mr, physaddr,
+                                     val, size, iotlbentry->attrs);
+    if (r != MEMTX_OK) {
+        cpu_transaction_failed(cpu, physaddr, addr, size, MMU_DATA_STORE,
+                               mmu_idx, iotlbentry->attrs, r, retaddr);
+    }
     if (locked) {
         qemu_mutex_unlock_iothread();
     }
@@ -845,6 +859,7 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env, target_ulong addr)
     MemoryRegion *mr;
     CPUState *cpu = ENV_GET_CPU(env);
     CPUIOTLBEntry *iotlbentry;
+    hwaddr physaddr;
 
     index = (addr >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
     mmu_idx = cpu_mmu_index(env, true);
@@ -868,6 +883,19 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env, target_ulong addr)
         }
         qemu_mutex_unlock_iothread();
 
+        /* Give the new-style cpu_transaction_failed() hook first chance
+         * to handle this.
+         * This is not the ideal place to detect and generate CPU
+         * exceptions for instruction fetch failure (for instance
+         * we don't know the length of the access that the CPU would
+         * use, and it would be better to go ahead and try the access
+         * and use the MemTXResult it produced). However it is the
+         * simplest place we have currently available for the check.
+         */
+        physaddr = (iotlbentry->addr & TARGET_PAGE_MASK) + addr;
+        cpu_transaction_failed(cpu, physaddr, addr, 0, MMU_INST_FETCH, mmu_idx,
+                               iotlbentry->attrs, MEMTX_DECODE_ERROR, 0);
+
         cpu_unassigned_access(cpu, addr, false, true, 0, 4);
         /* The CPU's unassigned access hook might have longjumped out
          * with an exception. If it didn't (or there was no hook) then
-- 
2.7.4