lkml.org 
[lkml]   [2018]   [Dec]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2] hpet: Fix missing '=' character in the __setup() code of hpet_mmap_enable
From
Date
On 12/20/18 7:39 PM, Greg KH wrote:
> On Thu, Dec 20, 2018 at 07:12:55PM +0530, Buland Singh wrote:
>> On 12/20/18 5:59 PM, Greg KH wrote:
>>> On Thu, Dec 20, 2018 at 05:35:24PM +0530, Buland Singh wrote:
>>>> Commit '3d035f580699 ("drivers/char/hpet.c: allow user controlled mmap for
>>>> user processes")' introduced a new kernel command line parameter hpet_mmap,
>>>> that is required to expose the memory map of the HPET registers to
>>>> user-space. Unfortunately the kernel command line parameter 'hpet_mmap' is
>>>> broken and never takes effect due to missing '=' character in the __setup()
>>>> code of hpet_mmap_enable.
>>>>
>>>> Before this patch:
>>>>
>>>> dmesg output with the kernel command line parameter hpet_mmap=1
>>>>
>>>> [ 0.204152] HPET mmap disabled
>>>>
>>>> dmesg output with the kernel command line parameter hpet_mmap=0
>>>>
>>>> [ 0.204192] HPET mmap disabled
>>>>
>>>> After this patch:
>>>>
>>>> dmesg output with the kernel command line parameter hpet_mmap=1
>>>>
>>>> [ 0.203945] HPET mmap enabled
>>>>
>>>> dmesg output with the kernel command line parameter hpet_mmap=0
>>>>
>>>> [ 0.204652] HPET mmap disabled
>>>>
>>>> Fixes: 3d035f580699 ("drivers/char/hpet.c: allow user controlled mmap for user processes")
>>>> Signed-off-by: Buland Singh <bsingh@redhat.com>
>>>> ---
>>>> drivers/char/hpet.c | 2 +-
>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
>>>> index 4a22b4b41aef..9bffcd37cc7b 100644
>>>> --- a/drivers/char/hpet.c
>>>> +++ b/drivers/char/hpet.c
>>>> @@ -377,7 +377,7 @@ static __init int hpet_mmap_enable(char *str)
>>>> pr_info("HPET mmap %s\n", hpet_mmap_enabled ? "enabled" : "disabled");
>>>> return 1;
>>>> }
>>>> -__setup("hpet_mmap", hpet_mmap_enable);
>>>> +__setup("hpet_mmap=", hpet_mmap_enable);
>>
>> Hello Greag,
>>
>>> This has _never_ worked? Since 3.13?
>>
>> Yes, that's true :)
>>
>>> Why not just remove the thing as it is obvious no one actually has ever used it. > That would make the code even simpler :)
>>
>> Data Plane Development Kit (DPDK)[1] provides API that requires the CONFIG_HPET_MMAP
>> kernel configuration option to be enabled[2]. Some end users might want to use the
>> HPET MMAP functionality within the application.
>
> But, obviously, they really don't need to do that from the kernel
> command line as no one has ever noticed this didn't work :)
>
> Also, that page:
>
>> [2] https://doc.dpdk.org/guides-18.08/linux_gsg/enable_func.html
>
> Does not say to use this command line option either. So if no one has
> ever used it, please, let us just delete it.
>
> thanks,
>
> greg k-h
>

Hello Greg,

It is better to allow a user to 'enable/disable' the HPET mmap from the
kernel command line as per the requirement rather than recompiling the
kernel to 'enable/disable' this functionality.

Also as per the description in the initial patch (commit 3d035f58), the
'CONFIG_HPET_MMAP' Kconfig option has a security risk involved. Hence,
keeping the CONFIG_HPET_MMAP_DEFAULT (disabled) and allowing a user to
alter the default behavior using the kernel command line parameter
hpet_mmap is a better solution.

Regards,
Buland Singh

\
 
 \ /
  Last update: 2018-12-21 13:19    [W:0.062 / U:0.672 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site