[Qemu-devel] [PATCH] MTRR support on x86, part 1

[Carl-Daniel Hailfinger]

The current codebase ignores MTRR (Memory Type Range Register)
configuration writes and reads because Qemu does not implement caching.
All BIOS/firmware in know of for x86 do implement a mode called
Cache-as-RAM (CAR) which locks down the CPU cache lines and uses the CPU
cache like RAM before RAM is enabled. Qemu assumes RAM is accessible
from the start, but it would be nice to be able to run real
BIOS/firmware in Qemu. For that, we need CAR support and for CAR support
we have to support MTRRs.

This patch is a first step in that direction. MTRRs are MSRs supported
by all recent x86 CPUs, even old i586. Besides influencing cache, the
MTRRs can be written and read back, so discarding MTRR writes violates
the expectations of existing code out there.
Handle common x86 MTRR reads and writes, but don't act on them.

One open question remains: Is CPUX86State initialized with zeros or do I
have to zero the MTRR settings stored there explicitly?

Signed-off-by: Carl-Daniel Hailfinger <address@hidden>

Index: target-i386/cpu.h
===================================================================
--- target-i386/cpu.h   (revision 5879)
+++ target-i386/cpu.h   (working copy)
@@ -261,8 +261,25 @@
 
 #define MSR_IA32_PERF_STATUS            0x198
 
+#define MSR_MTRRphysBase(reg)          (0x200 + 2 * (reg))
+#define MSR_MTRRphysMask(reg)          (0x200 + 2 * (reg) + 1)
+
+#define MSR_MTRRfix64K_00000           0x250
+#define MSR_MTRRfix16K_80000           0x258
+#define MSR_MTRRfix16K_A0000           0x259
+#define MSR_MTRRfix4K_C0000            0x268
+#define MSR_MTRRfix4K_C8000            0x269
+#define MSR_MTRRfix4K_D0000            0x26a
+#define MSR_MTRRfix4K_D8000            0x26b
+#define MSR_MTRRfix4K_E0000            0x26c
+#define MSR_MTRRfix4K_E8000            0x26d
+#define MSR_MTRRfix4K_F0000            0x26e
+#define MSR_MTRRfix4K_F8000            0x26f
+
 #define MSR_PAT                         0x277
 
+#define MSR_MTRRdefType                        0x2ff
+
 #define MSR_EFER                        0xc0000080
 
 #define MSR_EFER_SCE   (1 << 0)
@@ -629,6 +646,14 @@
     uint32_t cpuid_ext3_features;
     uint32_t cpuid_apic_id;
 
+    /* MTRRs */
+    uint64_t mtrr_fixed[11];
+    uint64_t mtrr_deftype;
+    struct {
+        uint64_t base;
+        uint64_t mask;
+    } mtrr_var[8];
+
 #ifdef USE_KQEMU
     int kqemu_enabled;
     int last_io_time;
Index: target-i386/op_helper.c
===================================================================
--- target-i386/op_helper.c     (revision 5879)
+++ target-i386/op_helper.c     (working copy)
@@ -3073,6 +3073,46 @@
         env->kernelgsbase = val;
         break;
 #endif
+    case MSR_MTRRphysBase(0):
+    case MSR_MTRRphysBase(1):
+    case MSR_MTRRphysBase(2):
+    case MSR_MTRRphysBase(3):
+    case MSR_MTRRphysBase(4):
+    case MSR_MTRRphysBase(5):
+    case MSR_MTRRphysBase(6):
+    case MSR_MTRRphysBase(7):
+        env->mtrr_var[((uint32_t)ECX - MSR_MTRRphysBase(0)) / 2].base = val;
+        break;
+    case MSR_MTRRphysMask(0):
+    case MSR_MTRRphysMask(1):
+    case MSR_MTRRphysMask(2):
+    case MSR_MTRRphysMask(3):
+    case MSR_MTRRphysMask(4):
+    case MSR_MTRRphysMask(5):
+    case MSR_MTRRphysMask(6):
+    case MSR_MTRRphysMask(7):
+        env->mtrr_var[((uint32_t)ECX - MSR_MTRRphysMask(0)) / 2].mask = val;
+        break;
+    case MSR_MTRRfix64K_00000:
+        env->mtrr_fixed[(uint32_t)ECX - MSR_MTRRfix64K_00000] = val;
+        break;
+    case MSR_MTRRfix16K_80000:
+    case MSR_MTRRfix16K_A0000:
+        env->mtrr_fixed[(uint32_t)ECX - MSR_MTRRfix16K_80000 + 1] = val;
+        break;
+    case MSR_MTRRfix4K_C0000:
+    case MSR_MTRRfix4K_C8000:
+    case MSR_MTRRfix4K_D0000:
+    case MSR_MTRRfix4K_D8000:
+    case MSR_MTRRfix4K_E0000:
+    case MSR_MTRRfix4K_E8000:
+    case MSR_MTRRfix4K_F0000:
+    case MSR_MTRRfix4K_F8000:
+        env->mtrr_fixed[(uint32_t)ECX - MSR_MTRRfix4K_C0000 + 3] = val;
+        break;
+    case MSR_MTRRdefType:
+        env->mtrr_deftype = val;
+        break;
     default:
         /* XXX: exception ? */
         break;
@@ -3145,6 +3185,46 @@
         }
         break;
 #endif
+    case MSR_MTRRphysBase(0):
+    case MSR_MTRRphysBase(1):
+    case MSR_MTRRphysBase(2):
+    case MSR_MTRRphysBase(3):
+    case MSR_MTRRphysBase(4):
+    case MSR_MTRRphysBase(5):
+    case MSR_MTRRphysBase(6):
+    case MSR_MTRRphysBase(7):
+        val = env->mtrr_var[((uint32_t)ECX - MSR_MTRRphysBase(0)) / 2].base;
+        break;
+    case MSR_MTRRphysMask(0):
+    case MSR_MTRRphysMask(1):
+    case MSR_MTRRphysMask(2):
+    case MSR_MTRRphysMask(3):
+    case MSR_MTRRphysMask(4):
+    case MSR_MTRRphysMask(5):
+    case MSR_MTRRphysMask(6):
+    case MSR_MTRRphysMask(7):
+        val = env->mtrr_var[((uint32_t)ECX - MSR_MTRRphysMask(0)) / 2].mask;
+        break;
+    case MSR_MTRRfix64K_00000:
+        val = env->mtrr_fixed[0];
+        break;
+    case MSR_MTRRfix16K_80000:
+    case MSR_MTRRfix16K_A0000:
+        val = env->mtrr_fixed[(uint32_t)ECX - MSR_MTRRfix16K_80000 + 1];
+        break;
+    case MSR_MTRRfix4K_C0000:
+    case MSR_MTRRfix4K_C8000:
+    case MSR_MTRRfix4K_D0000:
+    case MSR_MTRRfix4K_D8000:
+    case MSR_MTRRfix4K_E0000:
+    case MSR_MTRRfix4K_E8000:
+    case MSR_MTRRfix4K_F0000:
+    case MSR_MTRRfix4K_F8000:
+        val = env->mtrr_fixed[(uint32_t)ECX - MSR_MTRRfix4K_C0000 + 3];
+        break;
+    case MSR_MTRRdefType:
+        val = env->mtrr_deftype;
+        break;
     default:
         /* XXX: exception ? */
         val = 0;


-- 
http://www.hailfinger.org/