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

Janis Schoetterl-Glausch
2023-01-26T16:48:06Z

On Thu, 2023-01-26 at 14:02 +0100, Janosch Frank wrote:
> 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.

I just didn't like that much because it felt like an unspecific memop_do_things function.