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

Thomas Huth
2023-01-26T06:49:41Z

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

> - int r = 0;
> - const u64 supported_flags = KVM_S390_MEMOP_F_INJECT_EXCEPTION
> - | KVM_S390_MEMOP_F_CHECK_ONLY
> - | KVM_S390_MEMOP_F_SKEY_PROTECTION;
> + int r;
>
> - if (mop->flags & ~supported_flags || mop->ar >= NUM_ACRS || !mop->size)
> + r = mem_op_validate_common(mop, KVM_S390_MEMOP_F_INJECT_EXCEPTION |
> + KVM_S390_MEMOP_F_CHECK_ONLY |
> + KVM_S390_MEMOP_F_SKEY_PROTECTION);
> + if (r)
> + return r;
> + if (mop->ar >= NUM_ACRS)
> return -EINVAL;
> - if (mop->size > MEM_OP_MAX_SIZE)
> - return -E2BIG;
> if (kvm_s390_pv_cpu_is_protected(vcpu))
> 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);
>
> switch (mop->op) {
> case KVM_S390_MEMOP_LOGICAL_READ: