Messages in this thread | | | Date | Thu, 22 Sep 2022 13:07:22 -0700 | Subject | Re: [Intel-wired-lan] [PATCH] ixgbe: Use kmap_local_page in ixgbe_check_lbtest_frame() | From | Anirudh Venkataramanan <> |
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On 7/1/2022 8:36 AM, Fabio M. De Francesco wrote: > On giovedì 30 giugno 2022 23:59:23 CEST Alexander Duyck wrote: >> On Thu, Jun 30, 2022 at 11:18 AM Fabio M. De Francesco >> <fmdefrancesco@gmail.com> wrote: >>> >>> On giovedì 30 giugno 2022 18:09:18 CEST Alexander Duyck wrote: >>>> On Thu, Jun 30, 2022 at 8:25 AM Eric Dumazet <edumazet@google.com> > wrote: >>>>> >>>>> On Thu, Jun 30, 2022 at 5:17 PM Alexander Duyck >>>>> <alexander.duyck@gmail.com> wrote: >>>>>> >>>>>> On Thu, Jun 30, 2022 at 3:10 AM Maciej Fijalkowski >>>>>> <maciej.fijalkowski@intel.com> wrote: >>>>>>> >>>>>>> On Wed, Jun 29, 2022 at 10:58:36AM +0200, Fabio M. De Francesco >>> wrote: >>>>>>>> The use of kmap() is being deprecated in favor of >>> kmap_local_page(). >>>>>>>> >>>>>>>> With kmap_local_page(), the mapping is per thread, CPU local > and >>> not >>>>>>>> globally visible. Furthermore, the mapping can be acquired > from >>> any context >>>>>>>> (including interrupts). >>>>>>>> >>>>>>>> Therefore, use kmap_local_page() in > ixgbe_check_lbtest_frame() >>> because >>>>>>>> this mapping is per thread, CPU local, and not globally > visible. >>>>>>> >>>>>>> Hi, >>>>>>> >>>>>>> I'd like to ask why kmap was there in the first place and not > plain >>>>>>> page_address() ? >>>>>>> >>>>>>> Alex? >>>>>> >>>>>> The page_address function only works on architectures that have >>> access >>>>>> to all of physical memory via virtual memory addresses. The kmap >>>>>> function is meant to take care of highmem which will need to be >>> mapped >>>>>> before it can be accessed. >>>>>> >>>>>> For non-highmem pages kmap just calls the page_address function. >>>>>> https://elixir.bootlin.com/linux/latest/source/include/linux/ > highmem-internal.h#L40 >>>>> >>>>> >>>>> Sure, but drivers/net/ethernet/intel/ixgbe/ixgbe_main.c is > allocating >>>>> pages that are not highmem ? >>>>> >>>>> This kmap() does not seem needed. >>>> >>>> Good point. So odds are page_address is fine to use. Actually there > is >>>> a note to that effect in ixgbe_pull_tail. >>>> >>>> As such we could probably go through and update igb, and several of >>>> the other Intel drivers as well. >>>> >>>> - Alex >>>> >>> I don't know this code, however I know kmap*(). >>> >>> I assumed that, if author used kmap(), there was possibility that the > page >>> came from highmem. >>> >>> In that case kmap_local_page() looks correct here. >>> >>> However, now I read that that page _cannot_ come from highmem. > Therefore, >>> page_address() would suffice. >>> >>> If you all want I can replace kmap() / kunmap() with a "plain" >>> page_address(). Please let me know. >>> >>> Thanks, >>> >>> Fabio >> >> Replacing it with just page_address() should be fine. Back when I >> wrote the code I didn't realize that GFP_ATOMIC pages weren't >> allocated from highmem so I suspect I just used kmap since it was the >> way to cover all the bases. >> >> Thanks, >> >> - Alex >> > > OK, I'm about to prepare another patch with page_address() (obviously, this > should be discarded). > > Last thing... Is that page allocated with dma_pool_alloc() at > ixgbe/ixgbe_fcoe.c:196? Somewhere else? > > Thanks, > > Fabio > > P.S.: Can you say something about how pages are allocated in intel/e1000 > and in intel/e1000e? I see that those drivers use kmap_atomic().
Following Fabio's patches, I made similar changes for e1000/e1000e and submitted them to IWL [1].
Yesterday, Ira Weiny pointed me to some feedback from Dave Hansen on the use of page_address() [2]. My understanding of this feedback is that it's safer to use kmap_local_page() instead of page_address(), because you don't always know how the underlying page was allocated.
This approach (of using kmap_local_page() instead of page_address()) makes sense to me. Any reason not to go this way?
[1]
https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-1-anirudh.venkataramanan@intel.com/
https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-2-anirudh.venkataramanan@intel.com/
[2] https://lore.kernel.org/lkml/5d667258-b58b-3d28-3609-e7914c99b31b@intel.com/
Ani
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