From: Christoph Hellwig <hch@lst.de>
To: Julien Grall <julien.grall@arm.com>
Cc: Christoph Hellwig <hch@lst.de>, Arnd Bergmann <arnd@arndb.de>,
Robin Murphy <robin.murphy@arm.com>,
Juergen Gross <jgross@suse.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Mike Rapoport <rppt@linux.ibm.com>,
"open list:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
Joerg Roedel <jroedel@suse.de>,
xen-devel <xen-devel@lists.xenproject.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [Xen-devel] [PATCH] Revert "swiotlb: remove SWIOTLB_MAP_ERROR"
Date: Wed, 13 Mar 2019 19:32:54 +0100 [thread overview]
Message-ID: <20190313183254.GC4926@lst.de> (raw)
In-Reply-To: <124f4e49-9eb1-99d9-35f4-c2ef3dff8415@arm.com>
On Fri, Mar 08, 2019 at 05:25:57PM +0000, Julien Grall wrote:
> In the common case, Dom0 also contains the PV backend drivers. Those
> drivers may directly use the guest buffer in the DMA request (so a copy is
> avoided). To avoid using a bounce buffer too much, xen-swiotlb will find
> the host physical address associated to the guest buffer and will use it to
> compute the DMA address.
>
> While Dom0 kernel may only deal with 32-bit physical address, the
> hypervisor can still deal with up to 40-bit physical address. This means
> the guest memory can be allocated above the 4GB threshold. Hence why the
> dma_addr_t is always 64-bit with CONFIG_XEN=y.
This at least makes some sense. But is it really so much better to
avoid having a 64-bit phys_addr_t?
next prev parent reply other threads:[~2019-03-13 18:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-04 19:59 [PATCH] Revert "swiotlb: remove SWIOTLB_MAP_ERROR" Arnd Bergmann
2019-03-04 22:00 ` Konrad Rzeszutek Wilk
2019-03-04 23:56 ` Robin Murphy
2019-03-05 8:16 ` Arnd Bergmann
2019-03-05 9:41 ` [Xen-devel] " Julien Grall
2019-03-08 15:23 ` Christoph Hellwig
2019-03-08 17:25 ` Julien Grall
2019-03-13 18:32 ` Christoph Hellwig [this message]
2019-03-13 19:44 ` Arnd Bergmann
2019-03-05 9:36 ` Julien Grall
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