Re: [Xen-devel] [RFC PATCH 8/8]: PVH: privcmd changes

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-08-16 at 02:07 +0100, Mukesh Rathor wrote:
> ---
>  drivers/xen/privcmd.c |   68 +++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 66 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index ccee0f1..0a240ab 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -33,6 +33,7 @@
>  #include <xen/features.h>
>  #include <xen/page.h>
>  #include <xen/xen-ops.h>
> +#include <xen/balloon.h>
>  
>  #include "privcmd.h"
>  
> @@ -199,6 +200,10 @@ static long privcmd_ioctl_mmap(void __user *udata)
>       if (!xen_initial_domain())
>               return -EPERM;
>  
> +     /* PVH: TBD/FIXME. For now we only support privcmd_ioctl_mmap_batch */
> +     if (xen_pvh_domain())
> +             return -ENOSYS;
> +
>       if (copy_from_user(&mmapcmd, udata, sizeof(mmapcmd)))
>               return -EFAULT;
>  
> @@ -251,6 +256,8 @@ struct mmap_batch_state {
>       xen_pfn_t __user *user;
>  };
>  
> +/* PVH dom0: if domU being created is PV, then mfn is mfn(addr on bus). If
> + * it's PVH then mfn is pfn (input to HAP). */
>  static int mmap_batch_fn(void *data, void *state)
>  {
>       xen_pfn_t *mfnp = data;
> @@ -274,6 +281,40 @@ static int mmap_return_errors(void *data, void *state)
>       return put_user(*mfnp, st->user++);
>  }
>  
> +/* Allocate pfns that are then mapped with gmfns from foreign domid. Update
> + * the vma with the page info to use later.
> + * Returns: 0 if success, otherwise -errno
> + */
> +static int pvh_privcmd_resv_pfns(struct vm_area_struct *vma, int numpgs)
> +{
> +     int rc;
> +     struct xen_pvh_sav_pfn_info *savp;
> +
> +     savp = kzalloc(sizeof(struct xen_pvh_sav_pfn_info), GFP_KERNEL);
> +     if (savp == NULL)
> +             return -ENOMEM;
> +
> +     savp->sp_paga = kcalloc(numpgs, sizeof(savp->sp_paga[0]), GFP_KERNEL);
> +     if (savp->sp_paga == NULL) {
> +             kfree(savp);
> +             return -ENOMEM;
> +     }
> +
> +     rc = alloc_xenballooned_pages(numpgs, savp->sp_paga, 0);
> +     if (rc != 0) {
> +             pr_warn("%s Could not alloc %d pfns rc:%d\n", __FUNCTION__,
> +                     numpgs, rc);
> +             kfree(savp->sp_paga);
> +             kfree(savp);
> +             return -ENOMEM;
> +     }
> +     savp->sp_num_pgs = numpgs;
> +     BUG_ON(vma->vm_private_data);
> +     vma->vm_private_data = savp;
> +
> +     return 0;
> +}
> +
>  static struct vm_operations_struct privcmd_vm_ops;
>  
>  static long privcmd_ioctl_mmap_batch(void __user *udata)
> @@ -315,6 +356,12 @@ static long privcmd_ioctl_mmap_batch(void __user *udata)
>               goto out;
>       }
>  
> +     if (xen_pvh_domain()) {
> +             if ((ret=pvh_privcmd_resv_pfns(vma, m.num))) {
> +                     up_write(&mm->mmap_sem);
> +                     goto out;
> +             }
> +     }
>       state.domain = m.dom;
>       state.vma = vma;
>       state.va = m.addr;
> @@ -365,6 +412,19 @@ static long privcmd_ioctl(struct file *file,
>       return ret;
>  }
>  
> +static void privcmd_close(struct vm_area_struct *vma)
> +{
> +     struct xen_pvh_sav_pfn_info *savp;
> +
> +     if (!xen_pvh_domain() || ((savp=vma->vm_private_data) == NULL))
> +             return;
> +
> +     while (savp->sp_next_todo--) {
> +             xen_pfn_t pfn = page_to_pfn(savp->sp_paga[savp->sp_next_todo]);
> +             pvh_rem_xen_p2m(pfn, 1);
> +     }
> +}
> +
>  static int privcmd_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
>       printk(KERN_DEBUG "privcmd_fault: vma=%p %lx-%lx, pgoff=%lx, uv=%p\n",
> @@ -375,13 +435,14 @@ static int privcmd_fault(struct vm_area_struct *vma, 
> struct vm_fault *vmf)
>  }
>  
>  static struct vm_operations_struct privcmd_vm_ops = {
> +     .close = privcmd_close,
>       .fault = privcmd_fault
>  };
>  
>  static int privcmd_mmap(struct file *file, struct vm_area_struct *vma)
>  {
> -     /* Unsupported for auto-translate guests. */
> -     if (xen_feature(XENFEAT_auto_translated_physmap))
> +     /* Unsupported for auto-translate guests unless PVH */
> +     if (xen_feature(XENFEAT_auto_translated_physmap) && !xen_pvh_domain())
>               return -ENOSYS;
>  
>       /* DONTCOPY is essential for Xen because copy_page_range doesn't know
> @@ -395,6 +456,9 @@ static int privcmd_mmap(struct file *file, struct 
> vm_area_struct *vma)
>  
>  static int privcmd_enforce_singleshot_mapping(struct vm_area_struct *vma)
>  {
> +     if (xen_pvh_domain())
> +             return (vma->vm_private_data == NULL);
> +
>       return (xchg(&vma->vm_private_data, (void *)1) == NULL);

How come this is different for pvh?

Your version doesn't appear to enforce anything, since it doesn't set
it. Oh I see, you set it to some actual useful data in
pvh_privcmd_resv_pfns. I have a feeling you might want to use some sort
of atomic construct for that.

Which I suspect then means you need to be prepared for it to fail.

Can we set vm_private_data => 1 in privcmd_enforce_singleshot_mapping to
"open the transaction" and then up in pvh_privcmd_resv_pfns set it to
the final pointer up in pvh_privcmd_resv_pfns?

That was it would be non-NULL both while the mapping is being
constructed and in use. Might need some checks elsewhere that it is != 1
when you expect a real pointer.

Ian.



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