Messages in this thread | | | Subject | Re: [PATCH v2] hpet: Fix missing '=' character in the __setup() code of hpet_mmap_enable | From | Buland Singh <> | Date | Sun, 6 Jan 2019 19:39:29 +0530 |
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On 12/21/18 6:16 PM, Greg KH wrote: > On Fri, Dec 21, 2018 at 05:48:38PM +0530, Buland Singh wrote: >> 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. > > It might be "nice" but given that no one has noticed that this has never > worked, for all of the years that this has been present, that means to > me that no one has ever tried it because they really do not "need" it. > >> 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. > > Again, because no one has ever noticed that this was not working, why > not just rip it out until someone speaks up as to why they have to have > this feature and the other alternatives do not work for them? > > thanks, > > greg k-h >
Hello,
Adding Prarit to cc list for his opinion.
Regards, -- Buland Singh
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