netdev - [PATCH net v3 1/1] xsk: clear page contiguity bit when unmapping pool

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Message-Id: <20220628091848.534803-1-ivan.malov@oktetlabs.ru>
Date:   Tue, 28 Jun 2022 12:18:48 +0300
From:   Ivan Malov <ivan.malov@...etlabs.ru>
To:     Magnus Karlsson <magnus.karlsson@...el.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        netdev@...r.kernel.org
Cc:     Andrew Rybchenko <andrew.rybchenko@...etlabs.ru>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Björn Töpel <bjorn@...nel.org>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>
Subject: [PATCH net v3 1/1] xsk: clear page contiguity bit when unmapping pool

When a XSK pool gets mapped, xp_check_dma_contiguity() adds bit 0x1
to pages' DMA addresses that go in ascending order and at 4K stride.
The problem is that the bit does not get cleared before doing unmap.
As a result, a lot of warnings from iommu_dma_unmap_page() are seen
in dmesg, which indicates that lookups by iommu_iova_to_phys() fail.

Fixes: 2b43470add8c ("xsk: Introduce AF_XDP buffer allocation API")
Signed-off-by: Ivan Malov <ivan.malov@...etlabs.ru>
---
 v1 -> v2: minor adjustments to dispose of the "Fixes:" tag warning
 v2 -> v3: extra refinements to apply notes from Magnus Karlsson

 net/xdp/xsk_buff_pool.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
index 87bdd71c7bb6..f70112176b7c 100644
--- a/net/xdp/xsk_buff_pool.c
+++ b/net/xdp/xsk_buff_pool.c
@@ -332,6 +332,7 @@ static void __xp_dma_unmap(struct xsk_dma_map *dma_map, unsigned long attrs)
 	for (i = 0; i < dma_map->dma_pages_cnt; i++) {
 		dma = &dma_map->dma_pages[i];
 		if (*dma) {
+			*dma &= ~XSK_NEXT_PG_CONTIG_MASK;
 			dma_unmap_page_attrs(dma_map->dev, *dma, PAGE_SIZE,
 					     DMA_BIDIRECTIONAL, attrs);
 			*dma = 0;
-- 
2.30.2