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

On Thu, 2023-01-26 at 07:48 +0100, 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?

Yeah, I thought about it, but wasn't sure if I like moving the line down because of some people's insistence on reverse christmas tree. It's entirely arbitrary in a different way, but I like the return value being the last thing declared. In the end I forgot to make a decision on it.

...

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.

Yeah, that's fair.

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: