[Qemu-devel] [RFC PATCH] pc: align gpa<->hpa on 1GB boundary by splitting RAM on several regions

[Igor Mammedov <imammedo@redhat.com>]

Otherwise 1GB TLBs cannot be cached for the range.

PS:
as side effect we are not wasting ~1Gb of memory if
1Gb hugepages are used and -m "hpagesize(in Mb)*n + 1"

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
PS2:
As RFC it's yet without compatibility changes noted by Paolo

---
 exec.c                    |    8 ++++++-
 hw/i386/pc.c              |   50 ++++++++++++++++++++++++++++----------------
 include/exec/cpu-common.h |    1 +
 3 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/exec.c b/exec.c
index 9b6ea50..a4e5c80 100644
--- a/exec.c
+++ b/exec.c
@@ -882,7 +882,7 @@ void qemu_mutex_unlock_ramlist(void)
 
 #define HUGETLBFS_MAGIC       0x958458f6
 
-static long gethugepagesize(const char *path)
+long gethugepagesize(const char *path)
 {
     struct statfs fs;
     int ret;
@@ -925,6 +925,12 @@ static void *file_ram_alloc(RAMBlock *block,
         return NULL;
     }
 
+    /* refuse to use huge pages if requested size isn't page aligned
+     * to avoid wasting memory */
+    if (memory != (memory & ~(hpagesize-1))) {
+        return NULL;
+    }
+
     if (kvm_enabled() && !kvm_has_sync_mmu()) {
         fprintf(stderr, "host lacks kvm mmu notifiers, -mem-path unsupported\n");
         return NULL;
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 0c313fe..1611fa7 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1116,32 +1116,46 @@ FWCfgState *pc_memory_init(MemoryRegion *system_memory,
 {
     int linux_boot, i;
     MemoryRegion *ram, *option_rom_mr;
-    MemoryRegion *ram_below_4g, *ram_above_4g;
     FWCfgState *fw_cfg;
+    unsigned long hpagesize = gethugepagesize(mem_path);
+    ram_addr_t below_4g_mem_size_alined, below_4g_mem_size_tail, above_4g_mem_size_alined, above_4g_mem_size_tail;
 
     linux_boot = (kernel_filename != NULL);
 
-    /* Allocate RAM.  We allocate it as a single memory region and use
-     * aliases to address portions of it, mostly for backwards compatibility
-     * with older qemus that used qemu_ram_alloc().
-     */
+    *ram_memory = g_malloc(sizeof(**ram_memory));
+    memory_region_init(*ram_memory, NULL, "pc.ram",
+                       above_4g_mem_size == 0 ? below_4g_mem_size: 0x100000000ULL + above_4g_mem_size);
+    memory_region_add_subregion(system_memory, 0, *ram_memory);
+
+    below_4g_mem_size_alined = below_4g_mem_size & ~(hpagesize - 1);
     ram = g_malloc(sizeof(*ram));
-    memory_region_init_ram(ram, NULL, "pc.ram",
-                           below_4g_mem_size + above_4g_mem_size);
+    memory_region_init_ram(ram, NULL, "pc.ram.low.aligned", below_4g_mem_size_alined);
+    memory_region_add_subregion(*ram_memory, 0, ram);
     vmstate_register_ram_global(ram);
-    *ram_memory = ram;
-    ram_below_4g = g_malloc(sizeof(*ram_below_4g));
-    memory_region_init_alias(ram_below_4g, NULL, "ram-below-4g", ram,
-                             0, below_4g_mem_size);
-    memory_region_add_subregion(system_memory, 0, ram_below_4g);
-    if (above_4g_mem_size > 0) {
-        ram_above_4g = g_malloc(sizeof(*ram_above_4g));
-        memory_region_init_alias(ram_above_4g, NULL, "ram-above-4g", ram,
-                                 below_4g_mem_size, above_4g_mem_size);
-        memory_region_add_subregion(system_memory, 0x100000000ULL,
-                                    ram_above_4g);
+
+    below_4g_mem_size_tail = below_4g_mem_size - below_4g_mem_size_alined;
+    if (below_4g_mem_size_tail) {
+        ram = g_malloc(sizeof(*ram));
+        memory_region_init_ram(ram, NULL, "pc.ram.low.unaligned", below_4g_mem_size_tail);
+        memory_region_add_subregion(*ram_memory, below_4g_mem_size_alined, ram);
+        vmstate_register_ram_global(ram);
     }
 
+    if (above_4g_mem_size > 0) {
+        above_4g_mem_size_alined = above_4g_mem_size & ~(hpagesize - 1);
+        ram = g_malloc(sizeof(*ram));
+        memory_region_init_ram(ram, NULL, "pc.ram.high.aligned", above_4g_mem_size_alined);
+        memory_region_add_subregion(*ram_memory, 0x100000000ULL, ram);
+        vmstate_register_ram_global(ram);
+
+        above_4g_mem_size_tail = above_4g_mem_size - above_4g_mem_size_alined;
+        if (above_4g_mem_size_tail) {
+            ram = g_malloc(sizeof(*ram));
+            memory_region_init_ram(ram, NULL, "pc.ram.high.unaligned", above_4g_mem_size_tail);
+            memory_region_add_subregion(*ram_memory, 0x100000000ULL + above_4g_mem_size_alined, ram);
+            vmstate_register_ram_global(ram);
+	}
+    }
 
     /* Initialize PC system firmware */
     pc_system_firmware_init(rom_memory, guest_info->isapc_ram_fw);
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 40e15e4..f89a37c 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -57,6 +57,7 @@ void qemu_ram_set_idstr(ram_addr_t addr, const char *name, DeviceState *dev);
 #ifdef __linux__
 uint32_t qemu_get_ram_hpagesize(ram_addr_t addr);
 #endif
+long gethugepagesize(const char *path);
 
 void cpu_physical_memory_rw(hwaddr addr, uint8_t *buf,
                             int len, int is_write);
-- 
1.7.1