Re: [Qemu-devel] [PATCH 09/10] s390x/mmu: Use ioctl for reading and writing from/to guest memory

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

Am 21.04.2015 um 21:36 schrieb Alexander Graf:
> On 04/21/2015 09:34 PM, Christian Borntraeger wrote:
>> Am 21.04.2015 um 21:12 schrieb Alexander Graf:
>>> On 04/20/2015 04:55 PM, Christian Borntraeger wrote:
>>>> Am 09.04.2015 um 10:51 schrieb Cornelia Huck:
>>>>> From: Thomas Huth <thuth@linux.vnet.ibm.com>
>>>>>
>>>>> Add code to make use of the new ioctl for reading from / writing to
>>>>> virtual guest memory. By using the ioctl, the memory accesses are now
>>>>> protected with the so-called ipte-lock in the kernel.
>>>>>
>>>>> Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
>>>>> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
>>>> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>>>
>>>>> ---
>>>>>    target-s390x/cpu.h        |  7 +++++++
>>>>>    target-s390x/kvm.c        | 35 +++++++++++++++++++++++++++++++++++
>>>>>    target-s390x/mmu_helper.c |  9 +++++++++
>>>>>    3 files changed, 51 insertions(+)
>>>>>
>>>>> diff --git a/target-s390x/cpu.h b/target-s390x/cpu.h
>>>>> index 79bc80b..9c42743 100644
>>>>> --- a/target-s390x/cpu.h
>>>>> +++ b/target-s390x/cpu.h
>>>>> @@ -401,6 +401,8 @@ void kvm_s390_vcpu_interrupt(S390CPU *cpu, struct kvm_s390_irq *irq);
>>>>>    void kvm_s390_floating_interrupt(struct kvm_s390_irq *irq);
>>>>>    int kvm_s390_inject_flic(struct kvm_s390_irq *irq);
>>>>>    void kvm_s390_access_exception(S390CPU *cpu, uint16_t code, uint64_t te_code);
>>>>> +int kvm_s390_mem_op(S390CPU *cpu, vaddr addr, void *hostbuf, int len,
>>>>> +                    bool is_write);
>>>>>    int kvm_s390_get_clock(uint8_t *tod_high, uint64_t *tod_clock);
>>>>>    int kvm_s390_set_clock(uint8_t *tod_high, uint64_t *tod_clock);
>>>>>    #else
>>>>> @@ -418,6 +420,11 @@ static inline int kvm_s390_set_clock(uint8_t *tod_high, uint64_t *tod_low)
>>>>>    {
>>>>>        return -ENOSYS;
>>>>>    }
>>>>> +static inline int kvm_s390_mem_op(S390CPU *cpu, vaddr addr, void *hostbuf,
>>>>> +                                  int len, bool is_write)
>>>>> +{
>>>>> +    return -ENOSYS;
>>>>> +}
>>>>>    static inline void kvm_s390_access_exception(S390CPU *cpu, uint16_t code,
>>>>>                                                 uint64_t te_code)
>>>>>    {
>>>>> diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c
>>>>> index 619684b..e2ae2b3 100644
>>>>> --- a/target-s390x/kvm.c
>>>>> +++ b/target-s390x/kvm.c
>>>>> @@ -123,6 +123,7 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
>>>>>
>>>>>    static int cap_sync_regs;
>>>>>    static int cap_async_pf;
>>>>> +static int cap_mem_op;
>>>>>
>>>>>    static void *legacy_s390_alloc(size_t size, uint64_t *align);
>>>>>
>>>>> @@ -247,6 +248,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>>>>>    {
>>>>>        cap_sync_regs = kvm_check_extension(s, KVM_CAP_SYNC_REGS);
>>>>>        cap_async_pf = kvm_check_extension(s, KVM_CAP_ASYNC_PF);
>>>>> +    cap_mem_op = kvm_check_extension(s, KVM_CAP_S390_MEM_OP);
>>>>>
>>>>>        kvm_s390_enable_cmma(s);
>>>>>
>>>>> @@ -550,6 +552,39 @@ int kvm_s390_set_clock(uint8_t *tod_high, uint64_t *tod_low)
>>>>>        return kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, &attr);
>>>>>    }
>>>>>
>>>>> +/**
>>>>> + * kvm_s390_mem_op:
>>>>> + * @addr:      the logical start address in guest memory
>>>>> + * @hostbuf:   buffer in host memory. NULL = do only checks w/o copying
>>>>> + * @len:       length that should be transfered
>>>>> + * @is_write:  true = write, false = read
>>>>> + * Returns:    0 on success, non-zero if an exception or error occured
>>>>> + *
>>>>> + * Use KVM ioctl to read/write from/to guest memory. An access exception
>>>>> + * is injected into the vCPU in case of translation errors.
>>>>> + */
>>>>> +int kvm_s390_mem_op(S390CPU *cpu, vaddr addr, void *hostbuf, int len,
>>>>> +                    bool is_write)
>>>>> +{
>>>>> +    struct kvm_s390_mem_op mem_op = {
>>>>> +        .gaddr = addr,
>>>>> +        .flags = KVM_S390_MEMOP_F_INJECT_EXCEPTION,
>>>>> +        .size = len,
>>>>> +        .op = is_write ? KVM_S390_MEMOP_LOGICAL_WRITE
>>>>> +                       : KVM_S390_MEMOP_LOGICAL_READ,
>>>>> +        .buf = (uint64_t)hostbuf,
>>>>> +    };
>>>>> +
>>>>> +    if (!cap_mem_op) {
>>>>> +        return -ENOSYS;
>>>>> +    }
>>>>> +    if (!hostbuf) {
>>>>> +        mem_op.flags |= KVM_S390_MEMOP_F_CHECK_ONLY;
>>>>> +    }
>>>>> +
>>>>> +    return kvm_vcpu_ioctl(CPU(cpu), KVM_S390_MEM_OP, &mem_op);
>>>>> +}
>>>>> +
>>>>>    /*
>>>>>     * Legacy layout for s390:
>>>>>     * Older S390 KVM requires the topmost vma of the RAM to be
>>>>> diff --git a/target-s390x/mmu_helper.c b/target-s390x/mmu_helper.c
>>>>> index 9b88498..1e7412c 100644
>>>>> --- a/target-s390x/mmu_helper.c
>>>>> +++ b/target-s390x/mmu_helper.c
>>>>> @@ -450,6 +450,15 @@ int s390_cpu_virt_mem_rw(S390CPU *cpu, vaddr laddr, void *hostbuf,
>>>>>        target_ulong *pages;
>>>>>        int ret;
>>>>>
>>>>> +    if (kvm_enabled()) {
>>>>> +        ret = kvm_s390_mem_op(cpu, laddr, hostbuf, len, is_write);
>>>>> +        if (ret >= 0) {
>>>>> +            return ret;
>>>>> +        } else if (ret != -ENOSYS) {
>>>>> +            error_printf("kvm_s390_mem_op() failed: %s\n", strerror(-ret));
>>> Won't this spill the logs like crazy when running new qemu on old kernels?
>> kvm_s390_mem_op will return -ENOSYS if cap_mem_op is not set.
> 
> Oh, I see the logic now. Can you think of any way to make it more obvious to a reader what's going on?
> 
We could move the error_printf into kvm_s390_mem_op.
Well Conny has to do it as Thomas has left IBM.