Re: [PATCH v2 2/2] x86/mm/pat, drivers/media/ivtv: move pat warn and replace WARN() with pr_warn()

Ingo Molnar
2015-06-25T06:51:47Z

* Luis R. Rodriguez <mcgrof@do-not-panic.com> wrote:

> From: "Luis R. Rodriguez" <mcgrof@suse.com>
>
> On built-in kernels this warning will always splat as this is part
> of the module init. Fix that by shifting the PAT requirement check
> out under the code that does the "quasi-probe" for the device. This
> device driver relies on an existing driver to find its own devices,
> it looks for that device driver and its own found devices, then
> uses driver_for_each_device() to try to see if it can probe each of
> those devices as a frambuffer device with ivtvfb_init_card(). We
> tuck the PAT requiremenet check then on the ivtvfb_init_card()
> call making the check at least require an ivtv device present
> before complaining.
>
> Reported-by: Fengguang Wu <fengguang.wu@intel.com> [0-day test robot]
> Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
> ---
> drivers/media/pci/ivtv/ivtvfb.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/media/pci/ivtv/ivtvfb.c b/drivers/media/pci/ivtv/ivtvfb.c
> index 4cb365d..8b95eef 100644
> --- a/drivers/media/pci/ivtv/ivtvfb.c
> +++ b/drivers/media/pci/ivtv/ivtvfb.c
> @@ -38,6 +38,8 @@
> Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
> */
>
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> #include <linux/module.h>
> #include <linux/kernel.h>
> #include <linux/fb.h>
> @@ -1171,6 +1173,13 @@ static int ivtvfb_init_card(struct ivtv *itv)
> {
> int rc;
>
> +#ifdef CONFIG_X86_64
> + if (pat_enabled()) {
> + pr_warn("ivtvfb needs PAT disabled, boot with nopat kernel parameter\n");
> + return -ENODEV;
> + }
> +#endif
> +
> if (itv->osd_info) {
> IVTVFB_ERR("Card %d already initialised\n", ivtvfb_card_id);
> return -EBUSY;

Same argument as for ipath: why not make arch_phys_wc_add() fail on PAT and return
-1, and check it in arch_phys_wc_del()?

That way we don't do anything drastic, the remaining few drivers still keep
working (albeit suboptimally - can be worked around with the 'nopat' boot option)
- yet we've reduced the use of MTRRs drastically.

Thanks,

Ingo