From: Christoph Hellwig <hch@lst.de>
To: Michael Roth <mdroth@linux.vnet.ibm.com>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>,
Ram Pai <linuxram@us.ibm.com>,
mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org,
benh@kernel.crashing.org, david@gibson.dropbear.id.au,
paulus@ozlabs.org, hch@lst.de, andmike@us.ibm.com,
sukadev@linux.vnet.ibm.com, mst@redhat.com, ram.n.pai@gmail.com,
cai@lca.pw, tglx@linutronix.de, bauerman@linux.ibm.com,
linux-kernel@vger.kernel.org, leonardo@linux.ibm.com
Subject: Re: [PATCH v5 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VM.
Date: Wed, 11 Dec 2019 19:20:56 +0100 [thread overview]
Message-ID: <20191211182056.GA17052@lst.de> (raw)
In-Reply-To: <157608763756.3810.12346253559039287143@sif>
On Wed, Dec 11, 2019 at 12:07:17PM -0600, Michael Roth wrote:
> > io_tlb_start/io_tlb_end are only guaranteed to stay within 4GB and our
> > default DMA window is 1GB (KVM) or 2GB (PowerVM), ok, we can define
> > ARCH_LOW_ADDRESS_LIMIT as 1GB.
>
> True, and limiting allocations to under 1GB might be brittle (also saw a
> patching floating around that increased IO_TLB_DEFAULT_SIZE size to 1GB,
> which obviously wouldn't work out with this approach, but not sure if
> that's still needed or not: "powerpc/svm: Increase SWIOTLB buffer size")
FYI, there is a patch out there that allocates the powerpc swiotlb
from the boottom of the memblock area instead of the top to fix a 85xx
regression.
Also the AMD folks have been asking about non-GFP_DMA32 swiotlb pools
as they have the same bounce buffer issue with SEV. I think it is
entirely doable to have multiple swiotlb pool, I just need a volunteer
to implement that.
>
> However that's only an issue if we insist on using an identity mapping
> in the IOMMU, which would be nice because non-IOMMU virtio would
> magically work, but since that's not a goal of this series I think we do
> have the option of mapping io_tlb_start at DMA address 0 (or
> thereabouts).
>
> We'd probably need to modify __phys_to_dma to treat archdata.dma_offset
> as a negative offset in this case, but it seems like it would work about
> the same as with DDW offset.
Or switch to the generic version of __phys_to_dma that has a negative
offset. We'd just need to look into a signed value for dma_pfn_offset
to allow for the existing platforms that need the current positive
offset.
next prev parent reply other threads:[~2019-12-11 18:21 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-07 1:12 [PATCH v5 0/2] Enable IOMMU support for pseries Secure VMs Ram Pai
2019-12-07 1:12 ` [PATCH v5 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor Ram Pai
2019-12-07 1:12 ` [PATCH v5 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VM Ram Pai
2019-12-10 3:08 ` Alexey Kardashevskiy
2019-12-10 22:09 ` Thiago Jung Bauermann
2019-12-11 1:43 ` Michael Roth
2019-12-11 8:36 ` Alexey Kardashevskiy
2019-12-11 18:07 ` Michael Roth
2019-12-11 18:20 ` Christoph Hellwig [this message]
2019-12-12 6:45 ` Ram Pai
2019-12-13 0:19 ` Michael Roth
2019-12-10 3:07 ` [PATCH v5 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor Alexey Kardashevskiy
2019-12-10 5:12 ` Ram Pai
2019-12-10 5:32 ` Alexey Kardashevskiy
2019-12-10 15:35 ` Ram Pai
2019-12-11 8:15 ` Alexey Kardashevskiy
2019-12-11 20:31 ` Michael Roth
2019-12-11 22:47 ` Alexey Kardashevskiy
2019-12-12 2:39 ` Alexey Kardashevskiy
2019-12-13 0:22 ` Michael Roth
2019-12-12 4:11 ` Ram Pai
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