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

[Thomas Huth]

On Thu, 19 Feb 2015 10:47:29 +0100
Cornelia Huck <address@hidden> wrote:

> On Mon, 16 Feb 2015 13:16:41 +0100
> Thomas Huth <address@hidden> 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 <address@hidden>
> > ---
> >  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?

I like the idea with the capability ... I think I'll add that feature.

 Thomas