[Qemu-devel] [PATCH 1/5] Add target memory mapping API

[Avi Kivity <avi@redhat.com>]

Devices accessing large amounts of memory (as with DMA) will wish to obtain
a pointer to guest memory rather than access it indirectly via
cpu_physical_memory_rw().  Add a new API to convert target addresses to
host pointers.

In case the target address does not correspond to RAM, a bounce buffer is
allocated.  To prevent the guest from causing the host to allocate unbounded
amounts of bounce buffer, this memory is limited (currently to one page).

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 cpu-all.h |    6 +++
 exec.c    |  102 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 108 insertions(+), 0 deletions(-)

diff --git a/cpu-all.h b/cpu-all.h
index ee0a6e3..22ffaa7 100644
--- a/cpu-all.h
+++ b/cpu-all.h
@@ -923,6 +923,12 @@ static inline void cpu_physical_memory_write(target_phys_addr_t addr,
 {
     cpu_physical_memory_rw(addr, (uint8_t *)buf, len, 1);
 }
+void *cpu_physical_memory_map(target_phys_addr_t addr,
+                              target_phys_addr_t *plen,
+                              int is_write);
+void cpu_physical_memory_unmap(void *buffer, target_phys_addr_t len,
+                               int is_write, target_phys_addr_t access_len);
+
 uint32_t ldub_phys(target_phys_addr_t addr);
 uint32_t lduw_phys(target_phys_addr_t addr);
 uint32_t ldl_phys(target_phys_addr_t addr);
diff --git a/exec.c b/exec.c
index faa6333..6dd88fc 100644
--- a/exec.c
+++ b/exec.c
@@ -3045,6 +3045,108 @@ void cpu_physical_memory_write_rom(target_phys_addr_t addr,
     }
 }
 
+typedef struct {
+    void *buffer;
+    target_phys_addr_t addr;
+    target_phys_addr_t len;
+} BounceBuffer;
+
+static BounceBuffer bounce;
+
+/* Map a physical memory region into a host virtual address.
+ * May map a subset of the requested range, given by and returned in *plen.
+ * May return NULL if resources needed to perform the mapping are exhausted.
+ * Use only for reads OR writes - not for read-modify-write operations.
+ */
+void *cpu_physical_memory_map(target_phys_addr_t addr,
+                              target_phys_addr_t *plen,
+                              int is_write)
+{
+    target_phys_addr_t len = *plen;
+    target_phys_addr_t done = 0;
+    int l;
+    uint8_t *ret = NULL;
+    uint8_t *ptr;
+    target_phys_addr_t page;
+    unsigned long pd;
+    PhysPageDesc *p;
+    unsigned long addr1;
+
+    while (len > 0) {
+        page = addr & TARGET_PAGE_MASK;
+        l = (page + TARGET_PAGE_SIZE) - addr;
+        if (l > len)
+            l = len;
+        p = phys_page_find(page >> TARGET_PAGE_BITS);
+        if (!p) {
+            pd = IO_MEM_UNASSIGNED;
+        } else {
+            pd = p->phys_offset;
+        }
+
+        if ((pd & ~TARGET_PAGE_MASK) != IO_MEM_RAM) {
+            if (done || bounce.buffer) {
+                break;
+            }
+            bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, TARGET_PAGE_SIZE);
+            bounce.addr = addr;
+            bounce.len = l;
+            if (!is_write) {
+                cpu_physical_memory_rw(addr, bounce.buffer, l, 0);
+            }
+            ptr = bounce.buffer;
+        } else {
+            addr1 = (pd & TARGET_PAGE_MASK) + (addr & ~TARGET_PAGE_MASK);
+            ptr = phys_ram_base + addr1;
+        }
+        if (!done) {
+            ret = ptr;
+        } else if (ret + done != ptr) {
+            break;
+        }
+
+        len -= l;
+        addr += l;
+        done += l;
+    }
+    *plen = done;
+    return ret;
+}
+
+/* Unmaps a memory region previously mapped by cpu_physical_memory_map().
+ * Will also mark the memory as dirty if is_write == 1.  access_len gives
+ * the amount of memory that was actually read or written by the caller.
+ */
+void cpu_physical_memory_unmap(void *buffer, target_phys_addr_t len,
+                               int is_write, target_phys_addr_t access_len)
+{
+    if (buffer != bounce.buffer) {
+        if (is_write) {
+            unsigned long addr1 = (uint8_t *)buffer - phys_ram_base;
+            while (access_len) {
+                unsigned l;
+                l = TARGET_PAGE_SIZE;
+                if (l > access_len)
+                    l = access_len;
+                if (!cpu_physical_memory_is_dirty(addr1)) {
+                    /* invalidate code */
+                    tb_invalidate_phys_page_range(addr1, addr1 + l, 0);
+                    /* set dirty bit */
+                    phys_ram_dirty[addr1 >> TARGET_PAGE_BITS] |=
+                        (0xff & ~CODE_DIRTY_FLAG);
+                }
+                addr1 += l;
+                access_len -= l;
+            }
+        }
+        return;
+    }
+    if (is_write) {
+        cpu_physical_memory_write(bounce.addr, bounce.buffer, access_len);
+    }
+    qemu_free(bounce.buffer);
+    bounce.buffer = NULL;
+}
 
 /* warning: addr must be aligned */
 uint32_t ldl_phys(target_phys_addr_t addr)
-- 
1.6.0.6