[Qemu-devel] [PATCH QEMU] transparent hugepage support

[Andrea Arcangeli]

From: Andrea Arcangeli <address@hidden>

This will allow proper alignment so NPT/EPT can take advantage of linux host
backing the guest memory with hugepages (only relevant for KVM and not for QEMU
that has no NPT/EPT support). To complete it, it will also notify
the kernel that this memory is important to be backed by hugepages with
madvise (needed for both KVM and QEMU).

Signed-off-by: Andrea Arcangeli <address@hidden>
---

diff --git a/exec.c b/exec.c
index 891e0ee..aedd133 100644
--- a/exec.c
+++ b/exec.c
@@ -2628,11 +2628,25 @@ ram_addr_t qemu_ram_alloc(ram_addr_t size)
                                 PROT_EXEC|PROT_READ|PROT_WRITE,
                                 MAP_SHARED | MAP_ANONYMOUS, -1, 0);
 #else
-        new_block->host = qemu_vmalloc(size);
-#endif
+#if defined(__linux__) && defined(TARGET_HPAGE_BITS)
+       if (!kvm_enabled())
+#endif
+               new_block->host = qemu_vmalloc(size);
+#if defined(__linux__) && defined(TARGET_HPAGE_BITS)
+       else
+               /*
+                * Align on HPAGE_SIZE so "(gfn ^ pfn) &
+                * (HPAGE_SIZE-1) == 0" to allow KVM to take advantage
+                * of hugepages with NPT/EPT.
+                */
+               new_block->host = qemu_memalign(1 << TARGET_HPAGE_BITS, size);
+#endif 
 #ifdef MADV_MERGEABLE
         madvise(new_block->host, size, MADV_MERGEABLE);
 #endif
+#ifdef MADV_HUGEPAGE
+        madvise(new_block->host, size, MADV_HUGEPAGE);
+#endif
     }
     new_block->offset = last_ram_offset;
     new_block->length = size;
diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index ef7d951..26044eb 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -873,6 +873,7 @@ uint64_t cpu_get_tsc(CPUX86State *env);
 #define X86_DUMP_CCOP 0x0002 /* dump qemu flag cache */
 
 #define TARGET_PAGE_BITS 12
+#define TARGET_HPAGE_BITS (TARGET_PAGE_BITS+9)
 
 #define cpu_init cpu_x86_init
 #define cpu_exec cpu_x86_exec