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 21:12 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.