Re: [PATCH 1/4] hwmon: (f71805f) Use request_muxed_region for Super-IO accesses

[John Garry <john.garry@huawei.com>]

On 04/04/2019 19:33, Guenter Roeck wrote:
> Super-IO accesses may fail on a system with no or unmapped LPC bus.
>
> Unable to handle kernel paging request at virtual address ffffffbffee0002e
> pgd = ffffffc1d68d4000
> [ffffffbffee0002e] *pgd=0000000000000000, *pud=0000000000000000
> Internal error: Oops: 94000046 [#1] PREEMPT SMP
> Modules linked in: f71805f(+) hwmon
> CPU: 3 PID: 1659 Comm: insmod Not tainted 4.5.0+ #88
> Hardware name: linux,dummy-virt (DT)
> task: ffffffc1f6665400 ti: ffffffc1d6418000 task.ti: ffffffc1d6418000
> PC is at f71805f_find+0x6c/0x358 [f71805f]
>
> Also, other drivers may attempt to access the LPC bus at the same time,
> resulting in undefined behavior.
>
> Use request_muxed_region() to ensure that IO access on the requested
> address space is supported, and to ensure that access by multiple
> drivers is synchronized.
>
> Fixes: e53004e20a58e ("hwmon: New f71805f driver")
> Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> Reported-by: John Garry <john.garry@huawei.com>
> Cc: John Garry <john.garry@huawei.com>

Acked-by: John Garry <john.garry@huawei.com>

> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
>  drivers/hwmon/f71805f.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/hwmon/f71805f.c b/drivers/hwmon/f71805f.c
> index 73c681162653..623736d2a7c1 100644
> --- a/drivers/hwmon/f71805f.c
> +++ b/drivers/hwmon/f71805f.c
> @@ -96,17 +96,23 @@ superio_select(int base, int ld)
>  	outb(ld, base + 1);
>  }
>
> -static inline void
> +static inline int
>  superio_enter(int base)
>  {
> +	if (!request_muxed_region(base, 2, DRVNAME))
> +		return -EBUSY;
> +
>  	outb(0x87, base);
>  	outb(0x87, base);
> +
> +	return 0;
>  }
>
>  static inline void
>  superio_exit(int base)
>  {
>  	outb(0xaa, base);
> +	release_region(base, 2);
>  }
>
>  /*
> @@ -1561,7 +1567,7 @@ static int __init f71805f_device_add(unsigned short address,
>  static int __init f71805f_find(int sioaddr, unsigned short *address,
>  			       struct f71805f_sio_data *sio_data)
>  {
> -	int err = -ENODEV;
> +	int err;
>  	u16 devid;
>
>  	static const char * const names[] = {
> @@ -1569,8 +1575,11 @@ static int __init f71805f_find(int sioaddr, unsigned short *address,
>  		"F71872F/FG or F71806F/FG",
>  	};
>
> -	superio_enter(sioaddr);
> +	err = superio_enter(sioaddr);
> +	if (err)
> +		return err;
>
> +	err = -ENODEV;
>  	devid = superio_inw(sioaddr, SIO_REG_MANID);
>  	if (devid != SIO_FINTEK_ID)
>  		goto exit;
>