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

[Alexander Graf <agraf@suse.de>]

On 04/20/2015 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?


Alex

>> +        }
>> +    }
>> +
>>       nr_pages = (((laddr & ~TARGET_PAGE_MASK) + len - 1) >> TARGET_PAGE_BITS)
>>                  + 1;
>>       pages = g_malloc(nr_pages * sizeof(*pages));
>>