linux-kernel - Re: [RFC PATCH 10/11] powerpc/svm: Force the use of bounce buffers

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Message-ID: <20180824060055.GB13689@lst.de>
Date:   Fri, 24 Aug 2018 08:00:55 +0200
From:   Christoph Hellwig <hch@....de>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Alexey Kardashevskiy <aik@...abs.ru>,
        Anshuman Khandual <anshuman.linux@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mike Anderson <andmike@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Ram Pai <linuxram@...ibm.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 10/11] powerpc/svm: Force the use of bounce buffers

On Thu, Aug 23, 2018 at 11:59:32PM -0300, Thiago Jung Bauermann wrote:
> From: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> 
> SWIOTLB checks range of incoming CPU addresses to be bounced and see if the
> device can access it through it's DMA window without requiring bouncing. In
> such cases it just chooses to skip bouncing. But for cases like secure
> guests on powerpc platform all addresses need to be bounced into the shared
> pool of memory because the host cannot access it otherwise. Hence the need
> to do the bouncing is not related to device's DMA window. Hence force the
> use of bouncing by setting the swiotlb_force variable on secure guests.
> 
> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
> ---
>  arch/powerpc/kernel/svm.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/powerpc/kernel/svm.c b/arch/powerpc/kernel/svm.c
> index 1af5caa955f5..f0576ad65cd0 100644
> --- a/arch/powerpc/kernel/svm.c
> +++ b/arch/powerpc/kernel/svm.c
> @@ -17,6 +17,7 @@ static int __init init_svm(void)
>  		return 0;
>  
>  	ppc_swiotlb_enable = 1;
> +	swiotlb_force = SWIOTLB_FORCE;
>  	swiotlb_update_mem_attributes();

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