Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
NUMA balancing") set VM_IO flag to prevent grant maps from being
subjected to NUMA balancing.
It was discovered recently that this flag causes get_user_pages() to
always fail with -EFAULT.
check_vma_flags
__get_user_pages
__get_user_pages_locked
__get_user_pages_unlocked
get_user_pages_fast
iov_iter_get_pages
dio_refill_pages
do_direct_IO
do_blockdev_direct_IO
do_blockdev_direct_IO
ext4_direct_IO_read
generic_file_read_iter
aio_run_iocb
(which can happen if guest's vdisk has direct-io-safe option).
To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
NUMA balancing just as VM_IO does and has no effect on
check_vma_flags().
Reported-by: Olaf Hering <[email protected]>
Suggested-by: Hugh Dickins <[email protected]>
Signed-off-by: Boris Ostrovsky <[email protected]>
---
drivers/xen/gntdev.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index bb95212..2ef2b61 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -1007,7 +1007,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
vma->vm_ops = &gntdev_vmops;
- vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
+ vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
if (use_ptemod)
vma->vm_flags |= VM_DONTCOPY;
--
1.7.1
On Mon, 21 Nov 2016, Boris Ostrovsky wrote:
> Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
> NUMA balancing") set VM_IO flag to prevent grant maps from being
> subjected to NUMA balancing.
>
> It was discovered recently that this flag causes get_user_pages() to
> always fail with -EFAULT.
>
> check_vma_flags
> __get_user_pages
> __get_user_pages_locked
> __get_user_pages_unlocked
> get_user_pages_fast
> iov_iter_get_pages
> dio_refill_pages
> do_direct_IO
> do_blockdev_direct_IO
> do_blockdev_direct_IO
> ext4_direct_IO_read
> generic_file_read_iter
> aio_run_iocb
>
> (which can happen if guest's vdisk has direct-io-safe option).
>
> To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
> NUMA balancing just as VM_IO does and has no effect on
> check_vma_flags().
>
> Reported-by: Olaf Hering <[email protected]>
> Suggested-by: Hugh Dickins <[email protected]>
> Signed-off-by: Boris Ostrovsky <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
But nicer with the addition of a code comment saying
/* VM_MIXEDMAP to forbid NUMA balancing but permit get_user_pages() */
> ---
> drivers/xen/gntdev.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index bb95212..2ef2b61 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -1007,7 +1007,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>
> vma->vm_ops = &gntdev_vmops;
>
> - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
> + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
>
> if (use_ptemod)
> vma->vm_flags |= VM_DONTCOPY;
> --
> 1.7.1
On 22/11/16 04:59, Hugh Dickins wrote:
> On Mon, 21 Nov 2016, Boris Ostrovsky wrote:
>
>> Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
>> NUMA balancing") set VM_IO flag to prevent grant maps from being
>> subjected to NUMA balancing.
>>
>> It was discovered recently that this flag causes get_user_pages() to
>> always fail with -EFAULT.
>>
>> check_vma_flags
>> __get_user_pages
>> __get_user_pages_locked
>> __get_user_pages_unlocked
>> get_user_pages_fast
>> iov_iter_get_pages
>> dio_refill_pages
>> do_direct_IO
>> do_blockdev_direct_IO
>> do_blockdev_direct_IO
>> ext4_direct_IO_read
>> generic_file_read_iter
>> aio_run_iocb
>>
>> (which can happen if guest's vdisk has direct-io-safe option).
>>
>> To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
>> NUMA balancing just as VM_IO does and has no effect on
>> check_vma_flags().
>>
>> Reported-by: Olaf Hering <[email protected]>
>> Suggested-by: Hugh Dickins <[email protected]>
>> Signed-off-by: Boris Ostrovsky <[email protected]>
>
> Acked-by: Hugh Dickins <[email protected]>
>
> But nicer with the addition of a code comment saying
> /* VM_MIXEDMAP to forbid NUMA balancing but permit get_user_pages() */
I can fix that up when committing.
Juergen
>
>> ---
>> drivers/xen/gntdev.c | 2 +-
>> 1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
>> index bb95212..2ef2b61 100644
>> --- a/drivers/xen/gntdev.c
>> +++ b/drivers/xen/gntdev.c
>> @@ -1007,7 +1007,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>
>> vma->vm_ops = &gntdev_vmops;
>>
>> - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
>> + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
>>
>> if (use_ptemod)
>> vma->vm_flags |= VM_DONTCOPY;
>> --
>> 1.7.1
>
On Mon, Nov 21, Boris Ostrovsky wrote:
> Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
> NUMA balancing") set VM_IO flag to prevent grant maps from being
> subjected to NUMA balancing.
Tested-by: Olaf Hering <[email protected]>
This should go to stable as well.
Olaf
On 21/11/16 15:56, Boris Ostrovsky wrote:
> Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
> NUMA balancing") set VM_IO flag to prevent grant maps from being
> subjected to NUMA balancing.
>
> It was discovered recently that this flag causes get_user_pages() to
> always fail with -EFAULT.
>
> check_vma_flags
> __get_user_pages
> __get_user_pages_locked
> __get_user_pages_unlocked
> get_user_pages_fast
> iov_iter_get_pages
> dio_refill_pages
> do_direct_IO
> do_blockdev_direct_IO
> do_blockdev_direct_IO
> ext4_direct_IO_read
> generic_file_read_iter
> aio_run_iocb
>
> (which can happen if guest's vdisk has direct-io-safe option).
>
> To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
> NUMA balancing just as VM_IO does and has no effect on
> check_vma_flags().
>
> Reported-by: Olaf Hering <[email protected]>
> Suggested-by: Hugh Dickins <[email protected]>
> Signed-off-by: Boris Ostrovsky <[email protected]>
Applied to xen/tip.git for-linus-4.10
Juergen
> ---
> drivers/xen/gntdev.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index bb95212..2ef2b61 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -1007,7 +1007,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>
> vma->vm_ops = &gntdev_vmops;
>
> - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
> + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
>
> if (use_ptemod)
> vma->vm_flags |= VM_DONTCOPY;
>