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Date:   Wed, 8 Jun 2022 22:08:54 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Dongli Zhang <dongli.zhang@oracle.com>
Cc:     iommu@lists.linux-foundation.org, xen-devel@lists.xenproject.org,
        x86@kernel.org, linuxppc-dev@lists.ozlabs.org,
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        sstabellini@kernel.org, mpe@ellerman.id.au, konrad.wilk@oracle.com,
        mst@redhat.com, jasowang@redhat.com, joe.jin@oracle.com
Subject: Re: [PATCH RFC v1 3/7] swiotlb-xen: support highmem for xen specific
 code
Message-ID: <YqGAZoG6/pVX9NqN@infradead.org>
References: <20220609005553.30954-1-dongli.zhang@oracle.com>
 <20220609005553.30954-4-dongli.zhang@oracle.com>
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On Wed, Jun 08, 2022 at 05:55:49PM -0700, Dongli Zhang wrote:
> @@ -109,19 +110,25 @@ int xen_swiotlb_fixup(void *buf, unsigned long nslabs, bool high)
>  	int rc;
>  	unsigned int order = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT);
>  	unsigned int i, dma_bits = order + PAGE_SHIFT;
> +	unsigned int max_dma_bits = MAX_DMA32_BITS;
>  	dma_addr_t dma_handle;
>  	phys_addr_t p = virt_to_phys(buf);
>  
>  	BUILD_BUG_ON(IO_TLB_SEGSIZE & (IO_TLB_SEGSIZE - 1));
>  	BUG_ON(nslabs % IO_TLB_SEGSIZE);
>  
> +	if (high) {
> +		dma_bits = MAX_DMA64_BITS;
> +		max_dma_bits = MAX_DMA64_BITS;
> +	}
> +

I think you really want to pass the addressing bits or mask to the
remap callback and not do magic with a 'high' flag here.