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

[Alexander Graf <agraf@suse.de>]

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?


Alex