[RFC][PATCH] qemu-kvm: x86: Refactor persistent CPU state

[Jan Kiszka <jan.kiszka@web.de>]

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This patch reworks the KVM-related layout and encoding of the CPU state
to be saved to disk or migrated. The goal is to define a format, version
9, that is also acceptable for upstream and can later be merged into
QEMU. Besides unconditionally writing KVM states, this format compresses
interrupt_bitmap into a single number as there can be no more than one
pending IRQ at a time.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 target-i386/cpu.h     |    2 +-
 target-i386/machine.c |   57 +++++++++++++++++++++++++++++++++++--------------
 2 files changed, 42 insertions(+), 17 deletions(-)

diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index f054af1..e07b504 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -838,7 +838,7 @@ static inline int cpu_get_time_fast(void)
 #define cpu_signal_handler cpu_x86_signal_handler
 #define cpu_list x86_cpu_list
 
-#define CPU_SAVE_VERSION 8
+#define CPU_SAVE_VERSION 9
 
 /* MMU modes definitions */
 #define MMU_MODE0_SUFFIX _kernel
diff --git a/target-i386/machine.c b/target-i386/machine.c
index 399204d..18ba983 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -37,7 +37,8 @@ void cpu_save(QEMUFile *f, void *opaque)
     uint16_t fptag, fpus, fpuc, fpregs_format;
     uint32_t hflags;
     int32_t a20_mask;
-    int i;
+    int32_t pending_irq;
+    int i, bit;
 
     if (kvm_enabled()) {
         kvm_save_registers(env);
@@ -152,13 +153,21 @@ void cpu_save(QEMUFile *f, void *opaque)
         qemu_put_be64s(f, &env->mtrr_var[i].mask);
     }
 
-    if (kvm_enabled()) {
-        for (i = 0; i < sizeof(env->interrupt_bitmap)/8 ; i++) {
-            qemu_put_be64s(f, &env->interrupt_bitmap[i]);
+    /* KVM-related states */
+
+    /* There can only be one pending IRQ set in the bitmap at a time, so try
+       to find it and save its number instead (-1 for none). */
+    pending_irq = -1;
+    for (i = 0; i < sizeof(env->interrupt_bitmap)/2; i++) {
+        bit = ffs(((uint16_t *)env->interrupt_bitmap)[i]);
+        if (bit) {
+            pending_irq = i * 16 + bit;
+            break;
         }
-        qemu_put_be64s(f, &env->tsc);
-        qemu_put_be32s(f, &env->mp_state);
     }
+    qemu_put_sbe32s(f, &pending_irq);
+    qemu_put_be32s(f, &env->mp_state);
+    qemu_put_be64s(f, &env->tsc);
 }
 
 #ifdef USE_X86LDOUBLE
@@ -192,9 +201,9 @@ int cpu_load(QEMUFile *f, void *opaque, int version_id)
     uint32_t hflags;
     uint16_t fpus, fpuc, fptag, fpregs_format;
     int32_t a20_mask;
+    int32_t pending_irq;
 
-    if (version_id != 3 && version_id != 4 && version_id != 5
-        && version_id != 6 && version_id != 7 && version_id != 8)
+    if (version_id < 3 || version_id > CPU_SAVE_VERSION)
         return -EINVAL;
     for(i = 0; i < CPU_NB_REGS; i++)
         qemu_get_betls(f, &env->regs[i]);
@@ -339,6 +348,16 @@ int cpu_load(QEMUFile *f, void *opaque, int version_id)
         }
     }
 
+    if (version_id >= 9) {
+        qemu_get_sbe32s(f, &pending_irq);
+        memset(&env->interrupt_bitmap, 0, sizeof(env->interrupt_bitmap));
+        if (pending_irq >= 0) {
+            env->interrupt_bitmap[pending_irq / 64] |= 1 << (pending_irq % 64);
+        }
+        qemu_get_be32s(f, &env->mp_state);
+        qemu_get_be64s(f, &env->tsc);
+    }
+
     /* XXX: ensure compatiblity for halted bit ? */
     /* XXX: compute redundant hflags bits */
     env->hflags = hflags;
@@ -347,14 +366,20 @@ int cpu_load(QEMUFile *f, void *opaque, int version_id)
         /* when in-kernel irqchip is used, env->halted causes deadlock
            because no userspace IRQs will ever clear this flag */
         env->halted = 0;
-        for (i = 0; i < sizeof(env->interrupt_bitmap)/8; i++) {
-            qemu_get_be64s(f, &env->interrupt_bitmap[i]);
-        }
-        qemu_get_be64s(f, &env->tsc);
-        kvm_load_registers(env);
-        kvm_load_tsc(env);
-        if (version_id >= 5) {
-            qemu_get_be32s(f, &env->mp_state);
+        if (version_id < 9) {
+            for (i = 0; i < sizeof(env->interrupt_bitmap)/8; i++) {
+                qemu_get_be64s(f, &env->interrupt_bitmap[i]);
+            }
+            qemu_get_be64s(f, &env->tsc);
+            kvm_load_registers(env);
+            kvm_load_tsc(env);
+            if (version_id >= 5) {
+                qemu_get_be32s(f, &env->mp_state);
+                kvm_load_mpstate(env);
+            }
+        } else {
+            kvm_load_registers(env);
+            kvm_load_tsc(env);
             kvm_load_mpstate(env);
         }
     }


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