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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCHv5] Xen: Fix retry calls into PRIVCMD_MMAPBATCH*.
On Aug 23, 2013, at 1:10 PM, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> From: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
>
> 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.
>
> Permit subsequent calls to update a sub-range of the VMA, iff nothing
> is yet mapped in that range.
>
> Since it is now valid to call PRIVCMD_MMAPBATCH* multiple times, only
> set vma->vm_private_data if the parameters are valid and (if
> necessary) the pages for the auto_translated_physmap case have been
> allocated. This prevents subsequent calls from incorrectly entering
> the 'retry' path when there are no pages allocated etc.
>
> Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
Verified, thanks. Having said that, one nit below
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> ---
> V2: Fixed autotranslated physmap mode breakage introduced by V1.
> V3: Enforce full range mapping for first ioctl call on a given VMA.
> V4: Shuffle logic to minimize page table walking.
> V5: Juggle if statements to be more readable, correctly handle 2nd
> call if the first failed -- David.
> ---
> drivers/xen/privcmd.c | 83 +++++++++++++++++++++++++++++++++++++------------
> 1 files changed, 63 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index f8e5dd7..8e74590 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -43,9 +43,10 @@ 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_vma_range_is_mapped(
> + struct vm_area_struct *vma,
> + unsigned long addr,
> + unsigned long nr_pages);
>
> static long privcmd_ioctl_hypercall(void __user *udata)
> {
> @@ -225,9 +226,9 @@ static long privcmd_ioctl_mmap(void __user *udata)
> vma = find_vma(mm, msg->va);
> rc = -EINVAL;
>
> - if (!vma || (msg->va != vma->vm_start) ||
> - !privcmd_enforce_singleshot_mapping(vma))
> + if (!vma || (msg->va != vma->vm_start) || vma->vm_private_data)
> goto out_up;
> + vma->vm_private_data = PRIV_VMA_LOCKED;
> }
>
> state.va = vma->vm_start;
> @@ -358,7 +359,7 @@ static int alloc_empty_pages(struct vm_area_struct *vma,
> int numpgs)
> kfree(pages);
> return -ENOMEM;
> }
> - BUG_ON(vma->vm_private_data != PRIV_VMA_LOCKED);
> + BUG_ON(vma->vm_private_data != NULL);
> vma->vm_private_data = pages;
>
> return 0;
> @@ -421,19 +422,43 @@ 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)) {
> - up_write(&mm->mmap_sem);
> + vma->vm_ops != &privcmd_vm_ops) {
> ret = -EINVAL;
> - goto out;
> + goto out_unlock;
> }
> - if (xen_feature(XENFEAT_auto_translated_physmap)) {
> - ret = alloc_empty_pages(vma, m.num);
> - if (ret < 0) {
> - up_write(&mm->mmap_sem);
> - goto out;
> +
> + /*
> + * Caller must either:
> + *
> + * Map the whole VMA range, which will also allocate all the
> + * pages required for the auto_translated_physmap case.
> + *
> + * Or
> + *
> + * Map unmapped holes left from a previous map attempt (e.g.,
> + * because those foreign frames were previously paged out).
> + */
> + if (vma->vm_private_data == NULL) {
> + if (m.addr != vma->vm_start ||
> + m.addr + (nr_pages << PAGE_SHIFT) != vma->vm_end) {
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> + if (xen_feature(XENFEAT_auto_translated_physmap)) {
> + ret = alloc_empty_pages(vma, m.num);
> + if (ret < 0)
> + goto out_unlock;
> + } else
> + vma->vm_private_data = PRIV_VMA_LOCKED;
> + } else {
> + if (m.addr < vma->vm_start ||
> + m.addr + (nr_pages << PAGE_SHIFT) > vma->vm_end) {
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> + if (privcmd_vma_range_is_mapped(vma, m.addr, nr_pages)) {
> + ret = -EINVAL;
> + goto out_unlock;
> }
> }
>
> @@ -466,8 +491,11 @@ static long privcmd_ioctl_mmap_batch(void __user *udata,
> int version)
>
> out:
> free_page_list(&pagelist);
> -
> return ret;
> +
> +out_unlock:
> + up_write(&mm->mmap_sem);
> + goto out;
Backwards goto, double-yuck.
Andres
> }
>
> static long privcmd_ioctl(struct file *file,
> @@ -540,9 +568,24 @@ static int privcmd_mmap(struct file *file, struct
> vm_area_struct *vma)
> return 0;
> }
>
> -static int privcmd_enforce_singleshot_mapping(struct vm_area_struct *vma)
> +/*
> + * For MMAPBATCH*. This allows asserting the singleshot mapping
> + * on a per pfn/pte basis. Mapping calls that fail with ENOENT
> + * can be then retried until success.
> + */
> +static int is_mapped_fn(pte_t *pte, struct page *pmd_page,
> + unsigned long addr, void *data)
> +{
> + return pte_none(*pte) ? 0 : -EBUSY;
> +}
> +
> +static int privcmd_vma_range_is_mapped(
> + struct vm_area_struct *vma,
> + unsigned long addr,
> + unsigned long nr_pages)
> {
> - return !cmpxchg(&vma->vm_private_data, NULL, PRIV_VMA_LOCKED);
> + return apply_to_page_range(vma->vm_mm, addr, nr_pages << PAGE_SHIFT,
> + is_mapped_fn, NULL) != 0;
> }
>
> const struct file_operations xen_privcmd_fops = {
> --
> 1.7.2.5
>
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