Re: [PATCH v6 1/7] s390: ap: kvm: add PQAP interception for AQIC

[Tony Krowiak <akrowiak@linux.ibm.com>]

On 3/29/19 4:52 AM, Pierre Morel wrote:
> On 28/03/2019 17:12, Tony Krowiak wrote:
>> On 3/22/19 10:43 AM, Pierre Morel wrote:
>>> We prepare the interception of the PQAP/AQIC instruction for
>>> the case the AQIC facility is enabled in the guest.
>>>
>>> First of all we do not want to change existing behavior when
>>> intercepting AP instructions without the SIE allowing the guest
>>> to use AP instructions.
>>>
>>> In this patch we only handle the AQIC interception allowed by
>>> facility 65 which will be enabled when the complete interception
>>> infrastructure will be present.
>>>
>>> We add a callback inside the KVM arch structure for s390 for
>>> a VFIO driver to handle a specific response to the PQAP
>>> instruction with the AQIC command and only this command.
>>>
>>> But we want to be able to return a correct answer to the guest
>>> even there is no VFIO AP driver in the kernel.
>>> Therefor, we inject the correct exceptions from inside KVM for the
>>> case the callback is not initialized, which happens when the vfio_ap
>>> driver is not loaded.
>>>
>>> We do consider the responsability of the driver to always initialize
>>> the PQAP callback if it defines queues by initializing the CRYCB for
>>> a guest.
>>> If the callback has been setup we call it.
>>> If not we setup an answer considering that no queue is available
>>> for the guest when no callback has been setup.
>>>
>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>> ---
>>>   arch/s390/include/asm/kvm_host.h      |  8 ++++
>>>   arch/s390/kvm/priv.c                  | 90 
>>> +++++++++++++++++++++++++++++++++++
>>>   drivers/s390/crypto/vfio_ap_private.h |  2 +
>>>   3 files changed, 100 insertions(+)
>>>
>>> diff --git a/arch/s390/include/asm/kvm_host.h 
>>> b/arch/s390/include/asm/kvm_host.h
>>> index a496276..624460b 100644
>>> --- a/arch/s390/include/asm/kvm_host.h
>>> +++ b/arch/s390/include/asm/kvm_host.h
>>> @@ -18,6 +18,7 @@
>>>   #include <linux/kvm_host.h>
>>>   #include <linux/kvm.h>
>>>   #include <linux/seqlock.h>
>>> +#include <linux/module.h>
>>>   #include <asm/debug.h>
>>>   #include <asm/cpu.h>
>>>   #include <asm/fpu/api.h>
>>> @@ -721,8 +722,15 @@ struct kvm_s390_cpu_model {
>>>       unsigned short ibc;
>>>   };
>>> +struct kvm_s390_module_hook {
>>> +    int (*hook)(struct kvm_vcpu *vcpu);
>>> +    void *data;
>>> +    struct module *owner;
>>> +};
>>> +
>>>   struct kvm_s390_crypto {
>>>       struct kvm_s390_crypto_cb *crycb;
>>> +    struct kvm_s390_module_hook *pqap_hook;
>>>       __u32 crycbd;
>>>       __u8 aes_kw;
>>>       __u8 dea_kw;
>>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
>>> index 8679bd7..793e48a 100644
>>> --- a/arch/s390/kvm/priv.c
>>> +++ b/arch/s390/kvm/priv.c
>>> @@ -27,6 +27,7 @@
>>>   #include <asm/io.h>
>>>   #include <asm/ptrace.h>
>>>   #include <asm/sclp.h>
>>> +#include <asm/ap.h>
>>>   #include "gaccess.h"
>>>   #include "kvm-s390.h"
>>>   #include "trace.h"
>>> @@ -592,6 +593,93 @@ static int handle_io_inst(struct kvm_vcpu *vcpu)
>>>       }
>>>   }
>>> +/*
>>> + * handle_pqap: Handling pqap interception
>>> + * @vcpu: the vcpu having issue the pqap instruction
>>> + *
>>> + * We now support PQAP/AQIC instructions and we need to correctly
>>> + * answer the guest even if no dedicated driver's hook is available.
>>> + *
>>> + * The intercepting code calls a dedicated callback for this 
>>> instruction
>>> + * if a driver did register one in the CRYPTO satellite of the
>>> + * SIE block.
>>> + *
>>> + * For PQAP AQIC and TAPQ instructions, verify privilege and 
>>> specifications.
>>> + *
>>> + * If no callback available, the queues are not available, return 
>>> this to
>>> + * the caller.
>>> + * Else return the value returned by the callback.
>>> + */
>>> +static int handle_pqap(struct kvm_vcpu *vcpu)
>>> +{
>>> +    struct ap_queue_status status = {};
>>> +    unsigned long reg0;
>>> +    int ret;
>>> +    uint8_t fc;
>>> +
>>> +    /* Verify that the AP instruction are available */
>>> +    if (!ap_instructions_available())
>>> +        return -EOPNOTSUPP;
>>> +    /* Verify that the guest is allowed to use AP instructions */
>>> +    if (!(vcpu->arch.sie_block->eca & ECA_APIE))
>>> +        return -EOPNOTSUPP;
>>> +    /*
>>> +     * The only possibly intercepted instructions when AP 
>>> instructions are
>>> +     * available for the guest are AQIC and TAPQ with the t bit set
>>> +     * since we do not set IC.3 (FIII) we currently will not intercept
>>> +     * TAPQ.
>>> +     * The following code will only treat AQIC function code.
>>> +     */
>>> +    reg0 = vcpu->run->s.regs.gprs[0];
>>> +    fc = reg0 >> 24;
>>> +    if (fc != 0x03) {
>>> +        pr_warn("%s: Unexpected interception code 0x%02x\n",
>>> +            __func__, fc);
>>> +        return -EOPNOTSUPP;
>>> +    }
>>> +    /* All PQAP instructions are allowed for guest kernel only */
>>> +    if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
>>> +        return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
>>> +    /*
>>> +     * Common tests for PQAP instructions to generate a specification
>>> +     * exception
>>> +     */
>>> +    /* Zero bits overwrite produce a specification exception */
>>> +    if (reg0 & 0x007f0000UL)
>>> +        goto specification_except;
>>> +    /* If APXA is not installed APQN is limited */
>>> +    if (!(vcpu->kvm->arch.crypto.crycbd & 0x02))
>>> +        if (reg0 & 0x000030f0UL)
>>> +            goto specification_except;
>>> +    /* AQIC needs facility 65 */
>>> +    if (!test_kvm_facility(vcpu->kvm, 65))
>>> +        goto specification_except;
>>> +
>>> +    /*
>>> +     * Verify that the hook callback is registered, lock the owner
>>> +     * and call the hook.
>>> +     */
>>> +    if (vcpu->kvm->arch.crypto.pqap_hook) {
>>> +        if (!try_module_get(vcpu->kvm->arch.crypto.pqap_hook->owner))
>>> +            return -EOPNOTSUPP;
>>> +        ret = vcpu->kvm->arch.crypto.pqap_hook->hook(vcpu);
>>> +        module_put(vcpu->kvm->arch.crypto.pqap_hook->owner);
>>> +        return ret;
>>> +    }
>>> +    /*
>>> +     * It is the duty of the vfio_driver to register a hook
>>> +     * If it does not and we get an exception on AQIC we must
>>> +     * guess that there is no vfio_ap_driver at all and no one
>>> +     * to handle the guests's CRYCB and the CRYCB is empty.
>>> +     */
>>> +    status.response_code = 0x01;
>>> +    memcpy(&vcpu->run->s.regs.gprs[1], &status, sizeof(status));
>>> +    return 0;
>>> +
>>> +specification_except:
>>> +    return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
>>> +}
>>> +
>>>   static int handle_stfl(struct kvm_vcpu *vcpu)
>>>   {
>>>       int rc;
>>> @@ -878,6 +966,8 @@ int kvm_s390_handle_b2(struct kvm_vcpu *vcpu)
>>>           return handle_sthyi(vcpu);
>>>       case 0x7d:
>>>           return handle_stsi(vcpu);
>>> +    case 0xaf:
>>> +        return handle_pqap(vcpu);
>>>       case 0xb1:
>>>           return handle_stfl(vcpu);
>>>       case 0xb2:
>>> diff --git a/drivers/s390/crypto/vfio_ap_private.h 
>>> b/drivers/s390/crypto/vfio_ap_private.h
>>> index 76b7f98..a910be1 100644
>>> --- a/drivers/s390/crypto/vfio_ap_private.h
>>> +++ b/drivers/s390/crypto/vfio_ap_private.h
>>> @@ -16,6 +16,7 @@
>>>   #include <linux/mdev.h>
>>>   #include <linux/delay.h>
>>>   #include <linux/mutex.h>
>>> +#include <linux/kvm_host.h>
>>>   #include "ap_bus.h"
>>> @@ -81,6 +82,7 @@ struct ap_matrix_mdev {
>>>       struct ap_matrix matrix;
>>>       struct notifier_block group_notifier;
>>>       struct kvm *kvm;
>>> +    struct kvm_s390_module_hook pqap_hook;
>>
>> I don't understand the purpose of adding this field. We set up the
>> the kvm->arch.crypto.pqap_hook in the vfio_ap_mdev_set_kvm which is
>> also in this same file, why not just use a static struct 
>> kvm_s390_module_hook and reuse it when setting up
>> kvm->arch.crypto.pqap_hook? It saves you from initializing it every
>> time an ap_matrix_mdev is created.
> 
> Having this field embedded in the matrix_mdev allows to easily retrieve 
> the matrix_mdev from the the hook.

The only place you do this is in the handle_pqap hook. The reason you
get the matrix_mdev there is to get the vfio_ap_queue object from the
matrix_mdev qlist. You could just as well have gotten the vfio_ap_queue
using the vfio_ap_find_queue() function.

> 
> Thanks,
> Pierre
> 
> 
> 
>