linux-kernel - Re: [PATCH V4] RDMA/siw: Convert siw_tx_hdt() to kmap_local

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Date:   Thu, 15 Jul 2021 15:00:54 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     ira.weiny@...el.com
Cc:     Mike Marciniszyn <mike.marciniszyn@...nelisnetworks.com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Doug Ledford <dledford@...hat.com>,
        Faisal Latif <faisal.latif@...el.com>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Bernard Metzler <bmt@...ich.ibm.com>,
        Kamal Heib <kheib@...hat.com>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4] RDMA/siw: Convert siw_tx_hdt() to kmap_local_page()

On Thu, Jun 24, 2021 at 10:48:14AM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> kmap() is being deprecated and will break uses of device dax after PKS
> protection is introduced.[1]
> 
> The use of kmap() in siw_tx_hdt() is all thread local therefore
> kmap_local_page() is a sufficient replacement and will work with pgmap
> protected pages when those are implemented.
> 
> siw_tx_hdt() tracks pages used in a page_array.  It uses that array to
> unmap pages which were mapped on function exit.  Not all entries in the
> array are mapped and this is tracked in kmap_mask.
> 
> kunmap_local() takes a mapped address rather than a page.  Alter
> siw_unmap_pages() to take the iov array to reuse the iov_base address of
> each mapping.  Use PAGE_MASK to get the proper address for
> kunmap_local().
> 
> kmap_local_page() mappings are tracked in a stack and must be unmapped
> in the opposite order they were mapped in.  Because segments are mapped
> into the page array in increasing index order, modify siw_unmap_pages()
> to unmap pages in decreasing order.
> 
> Use kmap_local_page() instead of kmap() to map pages in the page_array.
> 
> [1] https://lore.kernel.org/lkml/20201009195033.3208459-59-ira.weiny@intel.com/
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> Reviewed-by: Bernard Metzler <bmt@...ich.ibm.com>
> ---
> Changes for V4:
> 	From Bernard
> 		Further optimize siw_unmap_pages() by eliminating the
> 		CRC page from the iov array.
> 
> Changes for V3:
> 	From Bernard
> 		Use 'p' in kmap_local_page()
> 		Use seg as length to siw_unmap_pages()
> 
> Changes for V2:
> 	From Bernard
> 		Reuse iov[].iov_base rather than declaring another array
> 		of pointers and preserve the use of kmap_mask to know
> 		which iov's were kmapped.
> ---
>  drivers/infiniband/sw/siw/siw_qp_tx.c | 30 +++++++++++++++++----------
>  1 file changed, 19 insertions(+), 11 deletions(-)

Applied to for-next, thanks

Jason