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

Janosch Frank
2022-04-26T07:18:30Z

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@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;
> + }
> }

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);