linux-kernel - Re: [PATCH 1/1] ixgbe: sync the first fragment unconditionally

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Date:   Tue, 06 Aug 2019 11:36:40 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     firo.yang@...e.com
Cc:     netdev@...r.kernel.org, jeffrey.t.kirsher@...el.com,
        intel-wired-lan@...ts.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ixgbe: sync the first fragment unconditionally

From: Firo Yang <firo.yang@...e.com>
Date: Tue, 6 Aug 2019 09:29:51 +0000

> In Xen environment, if Xen-swiotlb is enabled, ixgbe driver
> could possibly allocate a page, DMA memory buffer, for the first
> fragment which is not suitable for Xen-swiotlb to do DMA operations.
> Xen-swiotlb will internally allocate another page for doing DMA
> operations. It requires syncing between those two pages. Otherwise,
> we may get an incomplete skb. To fix this problem, sync the first
> fragment no matter the first fargment is makred as "page_released"
> or not.
> 
> Signed-off-by: Firo Yang <firo.yang@...e.com>

I don't understand, an unmap operation implies a sync operation.