linux-kernel - Re: [PATCH v2 1/2] KVM: s390: Don't indicate suppression on dirtying, failing memop

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Message-ID: <2be2e47d-c1f5-18ac-264d-a1bde3b03c24@linux.ibm.com>
Date:   Tue, 26 Apr 2022 09:18:18 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH v2 1/2] KVM: s390: Don't indicate suppression on dirtying,
 failing memop

On 4/25/22 12:01, Janis Schoetterl-Glausch 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 can modified guest memory, as a result, the likely
> correct ending is termination. Therefore do not indicate a
> suppressing instruction ending in this case.

Check grammar.

> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.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;
> +			}
>   		}

How about switching this around and masking those bits on termination.

>   		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));

Add a boolean variable named terminating, calculate the value before 
passing the boolean on.

>   out_unlock:
>   	if (need_ipte_lock)
>   		ipte_unlock(vcpu);