linux-kernel - Re: [PATCH RFC v1 3/7] swiotlb-xen: support highmem for xen specific code

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Date:   Wed, 8 Jun 2022 22:08:54 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Dongli Zhang <dongli.zhang@...cle.com>
Cc:     iommu@...ts.linux-foundation.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, hch@...radead.org,
        m.szyprowski@...sung.com, jgross@...e.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        sstabellini@...nel.org, mpe@...erman.id.au, konrad.wilk@...cle.com,
        mst@...hat.com, jasowang@...hat.com, joe.jin@...cle.com
Subject: Re: [PATCH RFC v1 3/7] swiotlb-xen: support highmem for xen specific
 code

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.