Commit 42cc8fa6 authored by Jan Kiszka's avatar Jan Kiszka Committed by Avi Kivity
Browse files

kvm: x86: Save/restore FPU OP, IP and DP 



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: default avatarJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent eb47d7c5

target-i386/cpu.h

+4 −0
Original line number Diff line number Diff line
@@ -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;

target-i386/kvm.c

+15 −5
Original line number Diff line number Diff line
@@ -753,6 +753,9 @@ 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;

    }
@@ -778,7 +781,7 @@ static int kvm_put_xsave(CPUState *env) 
#ifdef KVM_CAP_XSAVE

    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);
@@ -786,7 +789,7 @@ 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;
@@ -794,7 +797,9 @@ 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,
@@ -970,6 +975,9 @@ 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);

    }
@@ -985,7 +993,7 @@ static int kvm_get_xsave(CPUState *env) 
#ifdef KVM_CAP_XSAVE

    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);
@@ -1001,13 +1009,15 @@ 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);

target-i386/machine.c

+23 −0
Original line number Diff line number Diff line
@@ -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,
@@ -397,6 +417,9 @@ 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 */

        }