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[0/2] Dirtying, failing memop: don't indicate suppression

Message ID 20220401170247.1287354-1-scgl@linux.ibm.com
Headers show
Series Dirtying, failing memop: don't indicate suppression | expand

Message

Janis Schoetterl-Glausch April 1, 2022, 5:02 p.m. UTC 
If a memop fails due to key checked protection, after already having
written to the guest, don't indicate suppression to the guest, as that
would imply that memory wasn't modified.

This could be considered a fix to the code introducing storage key
support, however this is a bug in KVM only if we emulate an
instructions writing to an operand spanning multiple pages, which I
don't believe we do.

Janis Schoetterl-Glausch (2):
  KVM: s390: Don't indicate suppression on dirtying, failing memop
  KVM: s390: selftest: Test suppression indication on key prot exception

 arch/s390/kvm/gaccess.c                   | 47 ++++++++++++++---------
 tools/testing/selftests/kvm/s390x/memop.c | 43 ++++++++++++++++++++-
 2 files changed, 70 insertions(+), 20 deletions(-)


base-commit: 1ebdbeb03efe89f01f15df038a589077df3d21f5

Comments

Christian Borntraeger April 1, 2022, 5:13 p.m. UTC | #1 
Am 01.04.22 um 19:02 schrieb Janis Schoetterl-Glausch:
> 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 can modified guest memory. Therefore do not indicate a
> suppressing instruction ending in this case.

Make it explicit in the changelog that this is "terminating" instead of
"suppressing". z/VM has the same logic and the architecture allows for
terminating in those cases (even for ESOP2).
  >
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
> ---
>   arch/s390/kvm/gaccess.c | 47 ++++++++++++++++++++++++-----------------
>   1 file changed, 28 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index d53a183c2005..3b1fbef82288 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 suppress)
>   {
>   	struct kvm_s390_pgm_info *pgm = &vcpu->arch.pgm;
>   	struct trans_exc_code_bits *tec;
> @@ -503,22 +503,24 @@ static int trans_exc(struct kvm_vcpu *vcpu, int code, unsigned long gva,
>   
>   	switch (code) {
>   	case PGM_PROTECTION:
> -		switch (prot) {
> -		case PROT_TYPE_IEP:
> -			tec->b61 = 1;
> -			fallthrough;
> -		case PROT_TYPE_LA:
> -			tec->b56 = 1;
> -			break;
> -		case PROT_TYPE_KEYC:
> -			tec->b60 = 1;
> -			break;
> -		case PROT_TYPE_ALC:
> -			tec->b60 = 1;
> -			fallthrough;
> -		case PROT_TYPE_DAT:
> -			tec->b61 = 1;
> -			break;
> +		if (suppress) {
> +			switch (prot) {
> +			case PROT_TYPE_IEP:
> +				tec->b61 = 1;
> +				fallthrough;
> +			case PROT_TYPE_LA:
> +				tec->b56 = 1;
> +				break;
> +			case PROT_TYPE_KEYC:
> +				tec->b60 = 1;
> +				break;
> +			case PROT_TYPE_ALC:
> +				tec->b60 = 1;
> +				fallthrough;
> +			case PROT_TYPE_DAT:
> +				tec->b61 = 1;
> +				break;
> +			}
>   		}
>   		fallthrough;
>   	case PGM_ASCE_TYPE:
> @@ -552,6 +554,12 @@ 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, true);
> +}
> +
>   static int get_vcpu_asce(struct kvm_vcpu *vcpu, union asce *asce,
>   			 unsigned long ga, u8 ar, enum gacc_mode mode)
>   {
> @@ -1110,7 +1118,8 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>   		ga = kvm_s390_logical_to_effective(vcpu, ga + fragment_len);
>   	}
>   	if (rc > 0)
> -		rc = trans_exc(vcpu, rc, ga, ar, mode, prot);
> +		rc = trans_exc_ending(vcpu, rc, ga, ar, mode, prot,
> +				      (mode != GACC_STORE) || (idx == 0));
>   out_unlock:
>   	if (need_ipte_lock)
>   		ipte_unlock(vcpu);