netdev - [PATCH v2 net-next 2/6] sfc: Use kmap_local_page() instead of kmap

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Message-Id: <20221123205219.31748-3-anirudh.venkataramanan@intel.com>
Date:   Wed, 23 Nov 2022 12:52:15 -0800
From:   Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
To:     netdev@...r.kernel.org
Cc:     Ira Weiny <ira.weiny@...el.com>,
        "Fabio M . De Francesco" <fmdefrancesco@...il.com>,
        Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>
Subject: [PATCH v2 net-next 2/6] sfc: Use kmap_local_page() instead of kmap_atomic()

kmap_atomic() is being deprecated in favor of kmap_local_page(). Replace
kmap_atomic() and kunmap_atomic() with kmap_local_page() and kunmap_local()
respectively.

Note that kmap_atomic() disables preemption and page-fault processing, but
kmap_local_page() doesn't. When converting uses of kmap_atomic(), one has
to check if the code being executed between the map/unmap implicitly
depends on page-faults and/or preemption being disabled. If yes, then code
to disable page-faults and/or preemption should also be added for
functional correctness. That however doesn't appear to be the case here,
so just kmap_local_page() is used.

Also note that the page being mapped is not allocated by the driver, and so
the driver doesn't know if the page is in normal memory. This is the reason
kmap_local_page() is used as opposed to page_address().

I don't have hardware, so this change has only been compile tested.

Cc: Ira Weiny <ira.weiny@...el.com>
Cc: Fabio M. De Francesco <fmdefrancesco@...il.com>
Cc: Edward Cree <ecree.xilinx@...il.com>
Cc: Martin Habets <habetsm.xilinx@...il.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
---
v1 -> v2: Update commit message
---
 drivers/net/ethernet/sfc/tx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index c5f88f7..4ed4082 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -207,11 +207,11 @@ static void efx_skb_copy_bits_to_pio(struct efx_nic *efx, struct sk_buff *skb,
 		skb_frag_t *f = &skb_shinfo(skb)->frags[i];
 		u8 *vaddr;

-		vaddr = kmap_atomic(skb_frag_page(f));
+		vaddr = kmap_local_page(skb_frag_page(f));

 		efx_memcpy_toio_aligned_cb(efx, piobuf, vaddr + skb_frag_off(f),
 					   skb_frag_size(f), copy_buf);
-		kunmap_atomic(vaddr);
+		kunmap_local(vaddr);
 	}

 	EFX_WARN_ON_ONCE_PARANOID(skb_shinfo(skb)->frag_list);
-- 
2.37.2