linux-kernel - Re: [PATCH net] net: stmmac: Sync RX Buffer upon allocation

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Date:   Tue, 30 Jul 2019 10:26:38 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     Jose.Abreu@...opsys.com
Cc:     netdev@...r.kernel.org, Joao.Pinto@...opsys.com,
        peppe.cavallaro@...com, alexandre.torgue@...com,
        mcoquelin.stm32@...il.com,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        jonathanh@...dia.com
Subject: Re: [PATCH net] net: stmmac: Sync RX Buffer upon allocation

From: Jose Abreu <Jose.Abreu@...opsys.com>
Date: Tue, 30 Jul 2019 15:57:16 +0200

> With recent changes that introduced support for Page Pool in stmmac, Jon
> reported that NFS boot was no longer working on an ARM64 based platform
> that had the IP behind an IOMMU.
> 
> As Page Pool API does not guarantee DMA syncing because of the use of
> DMA_ATTR_SKIP_CPU_SYNC flag, we have to explicit sync the whole buffer upon
> re-allocation because we are always re-using same pages.
> 
> In fact, ARM64 code invalidates the DMA area upon two situations [1]:
> 	- sync_single_for_cpu(): Invalidates if direction != DMA_TO_DEVICE
> 	- sync_single_for_device(): Invalidates if direction == DMA_FROM_DEVICE
> 
> So, as we must invalidate both the current RX buffer and the newly allocated
> buffer we propose this fix.
> 
> [1] arch/arm64/mm/cache.S
> 
> Reported-by: Jon Hunter <jonathanh@...dia.com>
> Tested-by: Jon Hunter <jonathanh@...dia.com>
> Fixes: 2af6106ae949 ("net: stmmac: Introducing support for Page Pool")
> Signed-off-by: Jose Abreu <joabreu@...opsys.com>

Applied.