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SubjectRe: [PATCH] Xen: Fix retry calls into PRIVCMD_MMAPBATCH*.
On 09/08/13 15:11, Andres Lagar-Cavilla wrote:
> From: Andres Lagar-Cavilla <andres@lagarcavilla.org>
>
> When a foreign mapper attempts to map guest frames that are paged out,
> the mapper receives an ENOENT response and will have to try again
> while a helper process pages the target frame back in.
>
> Gating checks on PRIVCMD_MMAPBATCH* ioctl args were preventing retries
> of mapping calls.
>
> V2: Fixed autotranslated physmap mode breakage introduced by V1.
> V3: Enforce full range mapping for first ioctl call on a given VMA.
>
> Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
> ---
> drivers/xen/privcmd.c | 58 +++++++++++++++++++++++++++++++++++++++---------
> 1 files changed, 47 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index f8e5dd7..938e6e6 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -43,9 +43,12 @@ MODULE_LICENSE("GPL");
>
> #define PRIV_VMA_LOCKED ((void *)1)
>
> -#ifndef HAVE_ARCH_PRIVCMD_MMAP
> static int privcmd_enforce_singleshot_mapping(struct vm_area_struct *vma);
> -#endif
> +
> +static int privcmd_enforce_singleshot_mapping_granular(
> + struct vm_area_struct *vma,
> + unsigned long addr,
> + unsigned long nr_pages);
>
> static long privcmd_ioctl_hypercall(void __user *udata)
> {
> @@ -422,19 +425,26 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
> vma = find_vma(mm, m.addr);
> if (!vma ||
> vma->vm_ops != &privcmd_vm_ops ||
> - (m.addr != vma->vm_start) ||
> - ((m.addr + (nr_pages << PAGE_SHIFT)) != vma->vm_end) ||
> - !privcmd_enforce_singleshot_mapping(vma)) {
> + (m.addr < vma->vm_start) ||
> + ((m.addr + (nr_pages << PAGE_SHIFT)) > vma->vm_end) ||
> + !privcmd_enforce_singleshot_mapping_granular(vma, m.addr, nr_pages)) {
> up_write(&mm->mmap_sem);
> ret = -EINVAL;
> goto out;

I think this unnecessarily calls
privcmd_enforce_singleshot_mapping_granular() on the first call.

If you change the tests to the following, does it work for you?

/* Suitable VMA? */
if (!vma || vma->vm_ops != &privcmd_vm_ops)
// error

if (!privcmd_enforce_singleshot_mapping(..)) {
/* Already populated into this VMA once, are we populating a
subset that is not yet populated? */
if (is_subset_of_vma(vma, m,addr, nr_pages)
&& privcmd_enforce_single_shot_mapping_granular())
// ok
else
// error
} else {
/* Nothing populated in this VMA, must try to fully populate
it. */
if (is_all_of_vma(vma, m.addr, nr_pages))
// ok
else
// error
}


Thanks.

David


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