Re: [PATCH v6 08/14] KVM: s390: Move common code of mem_op functions into functions

Janosch Frank
2023-01-26T13:02:48Z

On 1/26/23 07:48, Thomas Huth wrote:
> On 25/01/2023 22.26, Janis Schoetterl-Glausch wrote:
>> The vcpu and vm mem_op ioctl implementations share some functionality.
>> Move argument checking and buffer allocation into functions and call
>> them from both implementations.
>> This allows code reuse in case of additional future mem_op operations.
>>
>> Suggested-by: Janosch Frank <frankja@linux.ibm.com>
>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
>> ---
>> arch/s390/kvm/kvm-s390.c | 80 +++++++++++++++++++++-------------------
>> 1 file changed, 42 insertions(+), 38 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index e4890e04b210..e0dfaa195949 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -2764,24 +2764,44 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
>> return r;
>> }
>>
>> -static bool access_key_invalid(u8 access_key)
>> +static int mem_op_validate_common(struct kvm_s390_mem_op *mop, u64 supported_flags)
>> {
>> - return access_key > 0xf;
>> + if (mop->flags & ~supported_flags || !mop->size)
>> + return -EINVAL;
>> + if (mop->size > MEM_OP_MAX_SIZE)
>> + return -E2BIG;
>> + if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {
>> + if (mop->key > 0xf)
>> + return -EINVAL;
>> + } else {
>> + mop->key = 0;
>> + }
>> + return 0;
>> +}
>> +
>> +static void *mem_op_alloc_buf(struct kvm_s390_mem_op *mop)
>> +{
>> + void *buf;
>> +
>> + if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)
>> + return NULL;
>> + buf = vmalloc(mop->size);
>> + if (!buf)
>> + return ERR_PTR(-ENOMEM);
>> + return buf;
>> }
>>
>> static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
>> {
>> void __user *uaddr = (void __user *)mop->buf;
>> - u64 supported_flags;
>> void *tmpbuf = NULL;
>
> You likely can now remove the "= NULL" here, I guess?
>
>> int r, srcu_idx;
>>
>> - supported_flags = KVM_S390_MEMOP_F_SKEY_PROTECTION
>> - | KVM_S390_MEMOP_F_CHECK_ONLY;
>> - if (mop->flags & ~supported_flags || !mop->size)
>> - return -EINVAL;
>> - if (mop->size > MEM_OP_MAX_SIZE)
>> - return -E2BIG;
>> + r = mem_op_validate_common(mop, KVM_S390_MEMOP_F_SKEY_PROTECTION |
>> + KVM_S390_MEMOP_F_CHECK_ONLY);
>> + if (r)
>> + return r;
>> +
>> /*
>> * This is technically a heuristic only, if the kvm->lock is not
>> * taken, it is not guaranteed that the vm is/remains non-protected.
>> @@ -2793,17 +2813,9 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
>> */
>> if (kvm_s390_pv_get_handle(kvm))
>> return -EINVAL;
>> - if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {
>> - if (access_key_invalid(mop->key))
>> - return -EINVAL;
>> - } else {
>> - mop->key = 0;
>> - }
>> - if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) {
>> - tmpbuf = vmalloc(mop->size);
>> - if (!tmpbuf)
>> - return -ENOMEM;
>> - }
>> + tmpbuf = mem_op_alloc_buf(mop);
>> + if (IS_ERR(tmpbuf))
>> + return PTR_ERR(tmpbuf);
>>
>> srcu_idx = srcu_read_lock(&kvm->srcu);
>>
>> @@ -5250,28 +5262,20 @@ static long kvm_s390_vcpu_mem_op(struct kvm_vcpu *vcpu,
>> {
>> void __user *uaddr = (void __user *)mop->buf;
>> void *tmpbuf = NULL;
>
> ... and here, too.
>
> But I have to admit that I'm also not sure whether I like the
> mem_op_alloc_buf() part or not (the mem_op_validate_common() part looks fine
> to me) : mem_op_alloc_buf() is a new function with 11 lines of code, and the
> old spots that allocate memory were only 5 lines of code each, so you now
> increased the LoC count and additionally have to fiddly with IS_ERR and
> PTR_ERR which is always a little bit ugly in my eyes ... IMHO I'd rather
> keep the old code here. But that's just my 0.02 €, if you think it's nicer
> with mem_op_alloc_buf(), I won't insist on keeping the old code.
>
> Thomas
>

I've done a PoC that has a **buff argument and combines the check with
the alloc.

@Nina: Any reason why this was split up?