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Re: [Xen-devel] [PATCH 2/2] xen/privcmd: add PRIVCMD_MMAPBATCH_V2 ioctl



On Aug 29, 2012, at 9:15 AM, David Vrabel wrote:

> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> PRIVCMD_MMAPBATCH_V2 extends PRIVCMD_MMAPBATCH with an additional
> field for reporting the error code for every frame that could not be
> mapped.  libxc prefers PRIVCMD_MMAPBATCH_V2 over PRIVCMD_MMAPBATCH.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> ---
> drivers/xen/privcmd.c |   78 +++++++++++++++++++++++++++++++++++++-----------
> include/xen/privcmd.h |   21 ++++++++++++-
> 2 files changed, 80 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index ccee0f1..ddd32cf 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -248,18 +248,23 @@ struct mmap_batch_state {
>       struct vm_area_struct *vma;
>       int err;
> 
> -     xen_pfn_t __user *user;
> +     xen_pfn_t __user *user_mfn;
> +     int __user *user_err;
> };
> 
> static int mmap_batch_fn(void *data, void *state)
> {
>       xen_pfn_t *mfnp = data;
> +     int *err = data;
Am I missing something or is there an aliasing here? Both mfnp and err point to 
data?
>       struct mmap_batch_state *st = state;
> +     int ret;
> 
> -     if (xen_remap_domain_mfn_range(st->vma, st->va & PAGE_MASK, *mfnp, 1,
> -                                    st->vma->vm_page_prot, st->domain) < 0) {
> -             *mfnp |= 0xf0000000U;
> -             st->err++;
> +     ret = xen_remap_domain_mfn_range(st->vma, st->va & PAGE_MASK, *mfnp, 1,
> +                                      st->vma->vm_page_prot, st->domain);
> +     if (ret < 0) {
> +             *err = ret;
> +             if (st->err == 0 || st->err == -ENOENT)
> +                     st->err = ret;
This will unset -ENOENT if a frame after an ENOENT error fails differently.

>       }
>       st->va += PAGE_SIZE;
> 
> @@ -268,18 +273,30 @@ static int mmap_batch_fn(void *data, void *state)
> 
> static int mmap_return_errors(void *data, void *state)
> {
> -     xen_pfn_t *mfnp = data;
> +     int *err = data;
>       struct mmap_batch_state *st = state;
> +     int ret;
> +
> +     if (st->user_err)
> +             return __put_user(*err, st->user_err++);
> +     else {
> +             xen_pfn_t mfn;
> 
> -     return put_user(*mfnp, st->user++);
> +             ret = __get_user(mfn, st->user_mfn);
> +             if (ret < 0)
> +                     return ret;
> +
> +             mfn |= PRIVCMD_MMAPBATCH_MFN_ERROR;
> +             return __put_user(mfn, st->user_mfn++);
> +     }
> }
> 
> static struct vm_operations_struct privcmd_vm_ops;
> 
> -static long privcmd_ioctl_mmap_batch(void __user *udata)
> +static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
> {
>       int ret;
> -     struct privcmd_mmapbatch m;
> +     struct privcmd_mmapbatch_v2 m;
>       struct mm_struct *mm = current->mm;
>       struct vm_area_struct *vma;
>       unsigned long nr_pages;
> @@ -289,15 +306,32 @@ static long privcmd_ioctl_mmap_batch(void __user *udata)
>       if (!xen_initial_domain())
>               return -EPERM;
> 
> -     if (copy_from_user(&m, udata, sizeof(m)))
> -             return -EFAULT;
> +     switch (version) {
> +     case 1:
> +             if (copy_from_user(&m, udata, sizeof(struct privcmd_mmapbatch)))
> +                     return -EFAULT;
> +             /* Returns per-frame error in m.arr. */
> +             m.err = NULL;
> +             if (!access_ok(VERIFY_WRITE, m.arr, m.num * sizeof(*m.arr)))
> +                     return -EFAULT;
> +             break;
> +     case 2:
> +             if (copy_from_user(&m, udata, sizeof(struct 
> privcmd_mmapbatch_v2)))
> +                     return -EFAULT;
> +             /* Returns per-frame error code in m.err. */
> +             if (!access_ok(VERIFY_WRITE, m.err, m.num * (sizeof(*m.err))))
> +                     return -EFAULT;
> +             break;
> +     default:
> +             return -EINVAL;
> +     }
> 
>       nr_pages = m.num;
>       if ((m.num <= 0) || (nr_pages > (LONG_MAX >> PAGE_SHIFT)))
>               return -EINVAL;
> 
>       ret = gather_array(&pagelist, m.num, sizeof(xen_pfn_t),
> -                        m.arr);
> +                        (xen_pfn_t *)m.arr);
> 
>       if (ret || list_empty(&pagelist))
>               goto out;
> @@ -325,12 +359,16 @@ static long privcmd_ioctl_mmap_batch(void __user *udata)
> 
>       up_write(&mm->mmap_sem);
> 
> -     if (state.err > 0) {
> -             state.user = m.arr;
> +     if (state.err) {
> +             state.user_mfn = (xen_pfn_t *)m.arr;
> +             state.user_err = m.err;
>               ret = traverse_pages(m.num, sizeof(xen_pfn_t),
> -                            &pagelist,
> -                            mmap_return_errors, &state);
> -     }
> +                                  &pagelist,
> +                                  mmap_return_errors, &state);
The callback now maps data to err (instead of mfnp … but I see no change to the 
gather_array other than a cast …am I missing something?

Thanks
Andres
> +             if (!ret)
> +                     ret = state.err;
> +     } else if (m.err)
> +             __clear_user(m.err, m.num * sizeof(*m.err));
> 
> out:
>       free_page_list(&pagelist);
> @@ -354,7 +392,11 @@ static long privcmd_ioctl(struct file *file,
>               break;
> 
>       case IOCTL_PRIVCMD_MMAPBATCH:
> -             ret = privcmd_ioctl_mmap_batch(udata);
> +             ret = privcmd_ioctl_mmap_batch(udata, 1);
> +             break;
> +
> +     case IOCTL_PRIVCMD_MMAPBATCH_V2:
> +             ret = privcmd_ioctl_mmap_batch(udata, 2);
>               break;
> 
>       default:
> diff --git a/include/xen/privcmd.h b/include/xen/privcmd.h
> index 17857fb..37e5255 100644
> --- a/include/xen/privcmd.h
> +++ b/include/xen/privcmd.h
> @@ -59,13 +59,30 @@ struct privcmd_mmapbatch {
>       int num;     /* number of pages to populate */
>       domid_t dom; /* target domain */
>       __u64 addr;  /* virtual address */
> -     xen_pfn_t __user *arr; /* array of mfns - top nibble set on err */
> +     xen_pfn_t __user *arr; /* array of mfns - or'd with
> +                               PRIVCMD_MMAPBATCH_MFN_ERROR on err */
> +};
> +
> +#define PRIVCMD_MMAPBATCH_MFN_ERROR 0xf0000000U
> +
> +struct privcmd_mmapbatch_v2 {
> +     unsigned int num; /* number of pages to populate */
> +     domid_t dom;      /* target domain */
> +     __u64 addr;       /* virtual address */
> +     const xen_pfn_t __user *arr; /* array of mfns */
> +     int __user *err;  /* array of error codes */
> };
> 
> /*
>  * @cmd: IOCTL_PRIVCMD_HYPERCALL
>  * @arg: &privcmd_hypercall_t
>  * Return: Value returned from execution of the specified hypercall.
> + *
> + * @cmd: IOCTL_PRIVCMD_MMAPBATCH_V2
> + * @arg: &struct privcmd_mmapbatch_v2
> + * Return: 0 if all pages were mapped successfully. -ENOENT if all
> + * failed mappings returned -ENOENT, otherwise the error code of the
> + * first failed mapping.
>  */
> #define IOCTL_PRIVCMD_HYPERCALL                                       \
>       _IOC(_IOC_NONE, 'P', 0, sizeof(struct privcmd_hypercall))
> @@ -73,5 +90,7 @@ struct privcmd_mmapbatch {
>       _IOC(_IOC_NONE, 'P', 2, sizeof(struct privcmd_mmap))
> #define IOCTL_PRIVCMD_MMAPBATCH                                       \
>       _IOC(_IOC_NONE, 'P', 3, sizeof(struct privcmd_mmapbatch))
> +#define IOCTL_PRIVCMD_MMAPBATCH_V2                           \
> +     _IOC(_IOC_NONE, 'P', 4, sizeof(struct privcmd_mmapbatch_v2))
> 
> #endif /* __LINUX_PUBLIC_PRIVCMD_H__ */
> -- 
> 1.7.2.5
> 


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