[PATCH v2][uq/master] kvm: x86: Save/restore FPU OP, IP and DP

Jan Kiszka
2011-06-15T13:17:36Z

These FPU states are properly maintained by KVM but not yet by TCG. So
far we unconditionally set them to 0 in the guest which may cause
state corruptions, though not with modern guests.

To avoid breaking backward migration, use a conditional subsection that
is only written if any of the three fields is non-zero. The guest's
FNINIT clears them frequently, and cleared IA32_MISC_ENABLE MSR[2]
reduces the probability of non-zero values further so that this
subsection is not expected to restrict migration in any common scenario.

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

Changes in v2:
- use conditional subsection

target-i386/cpu.h | 4 ++++
target-i386/kvm.c | 20 +++++++++++++++-----
target-i386/machine.c | 23 +++++++++++++++++++++++
3 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index 9c3340d..cdf68ff 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -641,6 +641,10 @@ typedef struct CPUX86State {
uint16_t fpuc;
uint8_t fptags[8]; /* 0 = valid, 1 = empty */
FPReg fpregs[8];
+ /* KVM-only so far */
+ uint16_t fpop;
+ uint64_t fpip;
+ uint64_t fpdp;

/* emulator internal variables */
float_status fp_status;
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 5ebb054..938e0a3 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -718,6 +718,9 @@ static int kvm_put_fpu(CPUState *env)
fpu.fsw = env->fpus & ~(7 << 11);
fpu.fsw |= (env->fpstt & 7) << 11;
fpu.fcw = env->fpuc;
+ fpu.last_opcode = env->fpop;
+ fpu.last_ip = env->fpip;
+ fpu.last_dp = env->fpdp;
for (i = 0; i < 8; ++i) {
fpu.ftwx |= (!env->fptags[i]) << i;
}
@@ -740,7 +743,7 @@ static int kvm_put_xsave(CPUState *env)
{
int i, r;
struct kvm_xsave* xsave;
- uint16_t cwd, swd, twd, fop;
+ uint16_t cwd, swd, twd;

if (!kvm_has_xsave()) {
return kvm_put_fpu(env);
@@ -748,7 +751,7 @@ static int kvm_put_xsave(CPUState *env)

xsave = qemu_memalign(4096, sizeof(struct kvm_xsave));
memset(xsave, 0, sizeof(struct kvm_xsave));
- cwd = swd = twd = fop = 0;
+ cwd = swd = twd = 0;
swd = env->fpus & ~(7 << 11);
swd |= (env->fpstt & 7) << 11;
cwd = env->fpuc;
@@ -756,7 +759,9 @@ static int kvm_put_xsave(CPUState *env)
twd |= (!env->fptags[i]) << i;
}
xsave->region[0] = (uint32_t)(swd << 16) + cwd;
- xsave->region[1] = (uint32_t)(fop << 16) + twd;
+ xsave->region[1] = (uint32_t)(env->fpop << 16) + twd;
+ memcpy(&xsave->region[XSAVE_CWD_RIP], &env->fpip, sizeof(env->fpip));
+ memcpy(&xsave->region[XSAVE_CWD_RDP], &env->fpdp, sizeof(env->fpdp));
memcpy(&xsave->region[XSAVE_ST_SPACE], env->fpregs,
sizeof env->fpregs);
memcpy(&xsave->region[XSAVE_XMM_SPACE], env->xmm_regs,
@@ -921,6 +926,9 @@ static int kvm_get_fpu(CPUState *env)
env->fpstt = (fpu.fsw >> 11) & 7;
env->fpus = fpu.fsw;
env->fpuc = fpu.fcw;
+ env->fpop = fpu.last_opcode;
+ env->fpip = fpu.last_ip;
+ env->fpdp = fpu.last_dp;
for (i = 0; i < 8; ++i) {
env->fptags[i] = !((fpu.ftwx >> i) & 1);
}
@@ -935,7 +943,7 @@ static int kvm_get_xsave(CPUState *env)
{
struct kvm_xsave* xsave;
int ret, i;
- uint16_t cwd, swd, twd, fop;
+ uint16_t cwd, swd, twd;

if (!kvm_has_xsave()) {
return kvm_get_fpu(env);
@@ -951,13 +959,15 @@ static int kvm_get_xsave(CPUState *env)
cwd = (uint16_t)xsave->region[0];
swd = (uint16_t)(xsave->region[0] >> 16);
twd = (uint16_t)xsave->region[1];
- fop = (uint16_t)(xsave->region[1] >> 16);
+ env->fpop = (uint16_t)(xsave->region[1] >> 16);
env->fpstt = (swd >> 11) & 7;
env->fpus = swd;
env->fpuc = cwd;
for (i = 0; i < 8; ++i) {
env->fptags[i] = !((twd >> i) & 1);
}
+ memcpy(&env->fpip, &xsave->region[XSAVE_CWD_RIP], sizeof(env->fpip));
+ memcpy(&env->fpdp, &xsave->region[XSAVE_CWD_RDP], sizeof(env->fpdp));
env->mxcsr = xsave->region[XSAVE_MXCSR];
memcpy(env->fpregs, &xsave->region[XSAVE_ST_SPACE],
sizeof env->fpregs);
diff --git a/target-i386/machine.c b/target-i386/machine.c
index bbeae88..d22a731 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -290,6 +290,26 @@ static const VMStateDescription vmstate_async_pf_msr = {
}
};

+static bool fpop_ip_dp_needed(void *opaque)
+{
+ CPUState *env = opaque;
+
+ return env->fpop != 0 || env->fpip != 0 || env->fpdp != 0;
+}
+
+static const VMStateDescription vmstate_fpop_ip_dp = {
+ .name = "cpu/fpop_ip_dp",
+ .version_id = 1,
+ .minimum_version_id = 1,
+ .minimum_version_id_old = 1,
+ .fields = (VMStateField []) {
+ VMSTATE_UINT16_V(fpop, CPUState, 13),
+ VMSTATE_UINT64_V(fpip, CPUState, 13),
+ VMSTATE_UINT64_V(fpdp, CPUState, 13),
+ VMSTATE_END_OF_LIST()
+ }
+};
+
static const VMStateDescription vmstate_cpu = {
.name = "cpu",
.version_id = CPU_SAVE_VERSION,
@@ -398,6 +418,9 @@ static const VMStateDescription vmstate_cpu = {
.vmsd = &vmstate_async_pf_msr,
.needed = async_pf_msr_needed,
} , {
+ .vmsd = &vmstate_fpop_ip_dp,
+ .needed = fpop_ip_dp_needed,
+ } , {
/* empty */
}
}