Re: [PATCH v3 1/2] KVM: s390: Don't indicate suppression on dirtying, failing memop

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Thu, 12 May 2022 15:10:17 +0200
Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote:

> If user space uses a memop to emulate an instruction and that
> memop fails, the execution of the instruction ends.
> Instruction execution can end in different ways, one of which is
> suppression, which requires that the instruction execute like a no-op.
> A writing memop that spans multiple pages and fails due to key
> protection may have modified guest memory, as a result, the likely
> correct ending is termination. Therefore, do not indicate a
> suppressing instruction ending in this case.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
>  Documentation/virt/kvm/api.rst |  6 ++++++
>  arch/s390/kvm/gaccess.c        | 22 ++++++++++++++++++----
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 4a900cdbc62e..b6aba4f50db7 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -3754,12 +3754,18 @@ in case of KVM_S390_MEMOP_F_CHECK_ONLY), the ioctl returns a positive
>  error number indicating the type of exception. This exception is also
>  raised directly at the corresponding VCPU if the flag
>  KVM_S390_MEMOP_F_INJECT_EXCEPTION is set.
> +On protection exceptions, unless specified otherwise, the injected
> +translation-exception identifier (TEID) indicates suppression.
>  
>  If the KVM_S390_MEMOP_F_SKEY_PROTECTION flag is set, storage key
>  protection is also in effect and may cause exceptions if accesses are
>  prohibited given the access key designated by "key"; the valid range is 0..15.
>  KVM_S390_MEMOP_F_SKEY_PROTECTION is available if KVM_CAP_S390_MEM_OP_EXTENSION
>  is > 0.
> +Since the accessed memory may span multiple pages and those pages might have
> +different storage keys, it is possible that a protection exception occurs
> +after memory has been modified. In this case, if the exception is injected,
> +the TEID does not indicate suppression.
>  
>  Absolute read/write:
>  ^^^^^^^^^^^^^^^^^^^^
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index d53a183c2005..227ed0009354 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -491,8 +491,8 @@ enum prot_type {
>  	PROT_TYPE_IEP  = 4,
>  };
>  
> -static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva,
> -		     u8 ar, enum gacc_mode mode, enum prot_type prot)
> +static int trans_exc_ending(struct kvm_vcpu *vcpu, int code, unsigned long gva, u8 ar,
> +			    enum gacc_mode mode, enum prot_type prot, bool terminate)
>  {
>  	struct kvm_s390_pgm_info *pgm = &vcpu->arch.pgm;
>  	struct trans_exc_code_bits *tec;
> @@ -520,6 +520,11 @@ static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva,
>  			tec->b61 = 1;
>  			break;
>  		}
> +		if (terminate) {
> +			tec->b56 = 0;
> +			tec->b60 = 0;
> +			tec->b61 = 0;
> +		}
>  		fallthrough;
>  	case PGM_ASCE_TYPE:
>  	case PGM_PAGE_TRANSLATION:
> @@ -552,6 +557,12 @@ static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva,
>  	return code;
>  }
>  
> +static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva, u8 ar,
> +		     enum gacc_mode mode, enum prot_type prot)
> +{
> +	return trans_exc_ending(vcpu, code, gva, ar, mode, prot, false);
> +}
> +
>  static int get_vcpu_asce(struct kvm_vcpu *vcpu, union asce *asce,
>  			 unsigned long ga, u8 ar, enum gacc_mode mode)
>  {
> @@ -1109,8 +1120,11 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>  		data += fragment_len;
>  		ga = kvm_s390_logical_to_effective(vcpu, ga + fragment_len);
>  	}
> -	if (rc > 0)
> -		rc = trans_exc(vcpu, rc, ga, ar, mode, prot);
> +	if (rc > 0) {
> +		bool terminate = (mode == GACC_STORE) && (idx > 0);
> +
> +		rc = trans_exc_ending(vcpu, rc, ga, ar, mode, prot, terminate);
> +	}
>  out_unlock:
>  	if (need_ipte_lock)
>  		ipte_unlock(vcpu);