Re: [Qemu-devel] [PATCH] KVM: s390: Add MEMOP ioctls for reading/writing guest memory

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Mon, 16 Feb 2015 13:16:41 +0100
Thomas Huth <thuth@linux.vnet.ibm.com> wrote:

> On s390, we've got to make sure to hold the IPTE lock while accessing
> logical memory. So let's add an ioctl for reading and writing logical
> memory to provide this feature for userspace, too.
> 
> Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
> ---
>  Documentation/virtual/kvm/api.txt |   45 +++++++++++++++++++++++
>  arch/s390/kvm/gaccess.c           |   22 +++++++++++
>  arch/s390/kvm/gaccess.h           |    2 +
>  arch/s390/kvm/kvm-s390.c          |   70 +++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/kvm.h          |   20 ++++++++++
>  5 files changed, 159 insertions(+), 0 deletions(-)

Looks good, except for one minor thing:


> +static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
> +				  struct kvm_s390_mem_op *mop)
> +{
> +	void __user *uaddr = (void __user *)mop->buf;
> +	void *tmpbuf = NULL;
> +	int r, srcu_idx;
> +	const u64 supported_flags = KVM_S390_MEMOP_F_INJECT_EXCEPTION
> +				    | KVM_S390_MEMOP_F_CHECK_ONLY;
> +
> +	if (mop->flags & ~supported_flags)
> +		return -EINVAL;
> +
> +	if (mop->size > 16 * PAGE_SIZE)
> +		return -E2BIG;

Do you want to document this limit? Or make it discoverable by having
the capability check return the number of pages?