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

Tony Krowiak
2019-03-27T16:06:53Z

On 3/26/19 2:57 PM, 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.
>
> The two paragraphs above should be described via the comments embedded
> in the code and is not necessary here.
>
>> + *
>> + * If no callback available, the queues are not available, return
>> this to
>> + * the caller.
>
> This implies it is specified via the return code when it is in fact
> the response code in the status word.
>
>> + * Else return the value returned by the callback.
>> + */
>
> Given this handler may be called for any PQAP instruction sub-function,
> I think the function doc should be more generic, providing:
>
> * A general description of what the function does
> * A description of each input parameter
> * A description of the value returned. If the return value is a return
>   code, the possible rc values can be enumerated with a description for
>   of the reason each particular value may be returned.
>
>> +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.
>> +     */
>
> Simplify to:
>
> /* The only supported PQAP function is AQIC (0x03) */
>
>> +    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 */
>
> There is only one PQAP instruction with multiple sub-functions.
> /* PQAP instruction is allowed for guest kernel only */
>                         or
> /* PQAP instruction is privileged */
>
>> +    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
>> +     */
>
> This comment is unnecessary as the individual comments below adequately
> do the job.
>
>> +    /* Zero bits overwrite produce a specification exception */
>
> This comment has no meaning unless you intimately know the architecture.
> The following would make more sense:
>
>     /* Bits 41-47 must all be zeros */
>
> It's probably not a big deal, but since we don't support PQAP(TAPQ),
> would it make more sense to make sure bits 40-47 are zeros (i.e.,
> the 't' bit is not set)?
>
>> +    if (reg0 & 0x007f0000UL)
>> +        goto specification_except;
>> +    /* If APXA is not installed APQN is limited */
>
> Wouldn't it be better to state how the APQN is limited?
> For example:
>
>     /*
>      * If APXA is not installed, then the maximum APID is
>      * 63 (bits 48-49 of reg0 must be zero) and the maximum
>      * APQI is 15 (bits 56-59 must be zero)
>      */
>
>> +    if (!(vcpu->kvm->arch.crypto.crycbd & 0x02))
>> +        if (reg0 & 0x000030f0UL)
>
> If APXA is not installed, then bits 48-49 and 56-59 must all be
> zeros. Shouldn't this mask be 0x0000c0f0UL?
>
>> +            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.
>> +     */
>
> The comment above does not make sense to me. If there is no pqap
> hook registered, then we need to handle that case for sure. But why
> mention getting an exception? Why even mention whose responsibility
> it is to set the hook when all we need to know is whether a hook is
> set or not?
>
> I am wondering whether merely setting a response code indicating the
> APQN is invalid is the correct thing to do here. First of all, if the
> guest's CRYCB is empty, then the AP bus running in the guest would not
> create any AP devices or any AP queues bound to any zcrypt driver. In
> that case, I don't think the PQAP(AQIC) would ever be issued. If a
> PQAP is intercepted, wouldn't we want to return -EOPNOTSUPP?

I dug back through the previous comments and see this has been discussed
before, so you can ignore this comment.

>
>
>
>> +    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.hhttps://www.linuxmint.com/start/sylvia/
>>
>> @@ -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;
>>   };
>>   extern int vfio_ap_mdev_register(void);
>>
>