[Qemu-devel] [PULL 4/9] roms: Flush icache when writing roms to guest memory

[Paolo Bonzini <pbonzini@redhat.com>]

From: Alexander Graf <agraf@suse.de>

We use the rom infrastructure to write firmware and/or initial kernel
blobs into guest address space. So we're basically emulating the cache
off phase on very early system bootup.

That phase is usually responsible for clearing the instruction cache for
anything it writes into cachable memory, to ensure that after reboot we
don't happen to execute stale bits from the instruction cache.

So we need to invalidate the icache every time we write a rom into guest
address space. We do not need to do this for every DMA since the guest
expects it has to flush the icache manually in that case.

This fixes random reboot issues on e5500 (booke ppc) for me.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 exec.c                    | 44 +++++++++++++++++++++++++++++++++++++++-----
 hw/core/loader.c          |  7 +++++++
 include/exec/cpu-common.h |  1 +
 3 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/exec.c b/exec.c
index f4b9ef2..896f7b8 100644
--- a/exec.c
+++ b/exec.c
@@ -50,6 +50,7 @@
 #include "translate-all.h"
 
 #include "exec/memory-internal.h"
+#include "qemu/cache-utils.h"
 
 //#define DEBUG_SUBPAGE
 
@@ -2010,9 +2011,13 @@ void cpu_physical_memory_rw(hwaddr addr, uint8_t *buf,
     address_space_rw(&address_space_memory, addr, buf, len, is_write);
 }
 
-/* used for ROM loading : can write in RAM and ROM */
-void cpu_physical_memory_write_rom(hwaddr addr,
-                                   const uint8_t *buf, int len)
+enum write_rom_type {
+    WRITE_DATA,
+    FLUSH_CACHE,
+};
+
+static inline void cpu_physical_memory_write_rom_internal(
+    hwaddr addr, const uint8_t *buf, int len, enum write_rom_type type)
 {
     hwaddr l;
     uint8_t *ptr;
@@ -2031,8 +2036,15 @@ void cpu_physical_memory_write_rom(hwaddr addr,
             addr1 += memory_region_get_ram_addr(mr);
             /* ROM/RAM case */
             ptr = qemu_get_ram_ptr(addr1);
-            memcpy(ptr, buf, l);
-            invalidate_and_set_dirty(addr1, l);
+            switch (type) {
+            case WRITE_DATA:
+                memcpy(ptr, buf, l);
+                invalidate_and_set_dirty(addr1, l);
+                break;
+            case FLUSH_CACHE:
+                flush_icache_range((uintptr_t)ptr, (uintptr_t)ptr + l);
+                break;
+            }
         }
         len -= l;
         buf += l;
@@ -2040,6 +2052,28 @@ void cpu_physical_memory_write_rom(hwaddr addr,
     }
 }
 
+/* used for ROM loading : can write in RAM and ROM */
+void cpu_physical_memory_write_rom(hwaddr addr,
+                                   const uint8_t *buf, int len)
+{
+    cpu_physical_memory_write_rom_internal(addr, buf, len, WRITE_DATA);
+}
+
+void cpu_flush_icache_range(hwaddr start, int len)
+{
+    /*
+     * This function should do the same thing as an icache flush that was
+     * triggered from within the guest. For TCG we are always cache coherent,
+     * so there is no need to flush anything. For KVM / Xen we need to flush
+     * the host's instruction cache at least.
+     */
+    if (tcg_enabled()) {
+        return;
+    }
+
+    cpu_physical_memory_write_rom_internal(start, NULL, len, FLUSH_CACHE);
+}
+
 typedef struct {
     MemoryRegion *mr;
     void *buffer;
diff --git a/hw/core/loader.c b/hw/core/loader.c
index 60d2ebd..0634bee 100644
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -785,6 +785,13 @@ static void rom_reset(void *unused)
             g_free(rom->data);
             rom->data = NULL;
         }
+        /*
+         * The rom loader is really on the same level as firmware in the guest
+         * shadowing a ROM into RAM. Such a shadowing mechanism needs to ensure
+         * that the instruction cache for that new region is clear, so that the
+         * CPU definitely fetches its instructions from the just written data.
+         */
+        cpu_flush_icache_range(rom->addr, rom->datasize);
     }
 }
 
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index e4996e1..8f33122 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -110,6 +110,7 @@ void stq_phys(hwaddr addr, uint64_t val);
 
 void cpu_physical_memory_write_rom(hwaddr addr,
                                    const uint8_t *buf, int len);
+void cpu_flush_icache_range(hwaddr start, int len);
 
 extern struct MemoryRegion io_mem_rom;
 extern struct MemoryRegion io_mem_notdirty;
-- 
1.8.3.1