Re: [Qemu-devel] [PATCH 1/3] s390/migration: Provide a cpu save for initial life migration work

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 21/11/12 16:02, Alexander Graf wrote:
> On 11/21/2012 03:59 PM, Christian Borntraeger wrote:
>> On 21/11/12 15:56, Alexander Graf wrote:
>>> On 11/21/2012 03:46 PM, Christian Borntraeger wrote:
>>>> This provides a simple cpu load and save function. With the recent
>>>> addition of sync regs we have the crs,acrs, the prefix and the
>>>> PSW already up to date. Lets also save the fpu via pre/post hooks.
>>>>
>>>> This patch also changes the license of machine.c to GPLv2 or later.
>>>> (The old code was just empty glue code, so there is no need
>>>> to go the "contributions after" way).
>>>>
>>>> Signed-off-by: Christian Borntraeger<borntraeger@de.ibm.com>
>>>> ---
>>>>    target-s390x/cpu.h     |    1 +
>>>>    target-s390x/machine.c |  115 ++++++++++++++++++++++++++++++++++++++++++------
>>>>    2 files changed, 103 insertions(+), 13 deletions(-)
>>>>
>>>> diff --git a/target-s390x/cpu.h b/target-s390x/cpu.h
>>>> index 0f9a1f7..ba695dd 100644
>>>> --- a/target-s390x/cpu.h
>>>> +++ b/target-s390x/cpu.h
>>>> @@ -27,6 +27,7 @@
>>>>    #define ELF_MACHINE    EM_S390
>>>>
>>>>    #define CPUArchState struct CPUS390XState
>>>> +#define CPU_SAVE_VERSION 1
>>>>
>>>>    #include "cpu-defs.h"
>>>>    #define TARGET_PAGE_BITS 12
>>>> diff --git a/target-s390x/machine.c b/target-s390x/machine.c
>>>> index 3e79be6..02706fd 100644
>>>> --- a/target-s390x/machine.c
>>>> +++ b/target-s390x/machine.c
>>>> @@ -2,29 +2,118 @@
>>>>     * QEMU S390x machine definitions
>>>>     *
>>>>     * Copyright (c) 2009 Alexander Graf<agraf@suse.de>
>>>> + * Copyright IBM Corp. 2012
>>>>     *
>>>> - * This library is free software; you can redistribute it and/or
>>>> - * modify it under the terms of the GNU Lesser General Public
>>>> - * License as published by the Free Software Foundation; either
>>>> - * version 2 of the License, or (at your option) any later version.
>>>> - *
>>>> - * This library is distributed in the hope that it will be useful,
>>>> - * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>>>> - * Lesser General Public License for more details.
>>>> - *
>>>> - * You should have received a copy of the GNU Lesser General Public
>>>> - * License along with this library; if not, see<http://www.gnu.org/licenses/>.
>>>> + * This work is licensed under the terms of the GNU GPL, version 2 or (at your
>>>> + * option) any later version.  See the COPYING file in the top-level directory.
>>>>     */
>>>>
>>>>    #include "hw/hw.h"
>>>>    #include "hw/boards.h"
>>>> +#include "cpu.h"
>>>> +#include "kvm.h"
>>>> +
>>>> +#if defined CONFIG_KVM
>>>> +static void cpu_pre_save(void *opaque)
>>>> +{
>>>> +    CPUS390XState *env = opaque;
>>>> +    struct kvm_fpu fpu;
>>>> +    int i, r;
>>>> +
>>>> +    if (!kvm_enabled()) {
>>>> +        return;
>>>> +    }
>>>> +
>>>> +    r = kvm_vcpu_ioctl(env, KVM_GET_FPU,&fpu);
>>>> +    assert(r == 0);
>>>> +    for (i = 0; i<   16; i++) {
>>>> +        env->fregs[i].ll = fpu.fprs[i];
>>>> +    }
>>>> +    env->fpc = fpu.fpc;
>>>> +}
>>>> +
>>>> +static int cpu_post_load(void *opaque, int version_id)
>>>> +{
>>>> +    CPUS390XState *env = opaque;
>>>> +    struct kvm_fpu fpu;
>>>> +    int i, r;
>>>> +
>>>> +    if (!kvm_enabled()) {
>>>> +        return 0;
>>>> +    }
>>>> +
>>>> +    for (i = 0; i<   16; i++) {
>>>> +        fpu.fprs[i] = env->fregs[i].ll;
>>>> +    }
>>>> +    fpu.fpc = env->fpc;
>>>> +
>>>> +    r = kvm_vcpu_ioctl(env, KVM_SET_FPU,&fpu);
>>>> +    assert(r == 0);
>>>> +
>>>> +    return 0;
>>>> +}
>>> The kvm register sync needs to happen in the kvm register sync function :)
>> That would eliminate the whole purpose of sync regs and forces us to have an
>> expensive ioctl on lots of exits (again). I would prefer to sync the registers
>> that we never need in qemu just here.
> 
> That's why the register sync has different stages.

Not the get_register. Which is called on every synchronize_state. Which happen quite often
on s390.