thr3ads.net - Linux Virtualization - [RFC PATCH] vring: Force use of DMA API for ARM-based systems [Jan 2017]

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Will Deacon

2016-Dec-20 15:14 UTC

[RFC PATCH] vring: Force use of DMA API for ARM-based systems

Booting Linux on an ARM fastmodel containing an SMMU emulation results
in an unexpected I/O page fault from the legacy virtio-blk PCI device:

[    1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received:
[    1.211800] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
[    1.211880] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
[    1.211959] arm-smmu-v3 2b400000.smmu:	0x00000008fa081002
[    1.212075] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
[    1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received:
[    1.212234] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
[    1.212314] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
[    1.212394] arm-smmu-v3 2b400000.smmu:	0x00000008fa081000
[    1.212471] arm-smmu-v3 2b400000.smmu:	0x0000000000000000

<system hangs failing to read partition table>

This is because the virtio-blk is behind an SMMU, so we have consequently
swizzled its DMA ops and configured the SMMU to translate accesses. This
then requires the vring code to use the DMA API to establish translations,
otherwise all transactions will result in fatal faults and termination.

Given that ARM-based systems only see an SMMU if one is really present
(the topology is all described by firmware tables such as device-tree or
IORT), then we can safely use the DMA API for all virtio devices.

Cc: Andy Lutomirski <luto at kernel.org>
Cc: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
---
 drivers/virtio/virtio_ring.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index ed9c9eeedfe5..06b91e29d1b7 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -159,6 +159,10 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
 	if (xen_domain())
 		return true;
 
+	/* On ARM-based machines, the DMA ops will do the right thing */
+	if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64))
+		return true;
+
 	return false;
 }
 
-- 
2.1.4

Marc Zyngier

2016-Dec-20 16:50 UTC

head link

[RFC PATCH] vring: Force use of DMA API for ARM-based systems

On 20/12/16 15:14, Will Deacon wrote:> Booting Linux on an ARM fastmodel containing an SMMU emulation results
> in an unexpected I/O page fault from the legacy virtio-blk PCI device:
> 
> [    1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received:
> [    1.211800] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
> [    1.211880] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
> [    1.211959] arm-smmu-v3 2b400000.smmu:	0x00000008fa081002
> [    1.212075] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
> [    1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received:
> [    1.212234] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
> [    1.212314] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
> [    1.212394] arm-smmu-v3 2b400000.smmu:	0x00000008fa081000
> [    1.212471] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
> 
> <system hangs failing to read partition table>
> 
> This is because the virtio-blk is behind an SMMU, so we have consequently
> swizzled its DMA ops and configured the SMMU to translate accesses. This
> then requires the vring code to use the DMA API to establish translations,
> otherwise all transactions will result in fatal faults and termination.
> 
> Given that ARM-based systems only see an SMMU if one is really present
> (the topology is all described by firmware tables such as device-tree or
> IORT), then we can safely use the DMA API for all virtio devices.
> 
> Cc: Andy Lutomirski <luto at kernel.org>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Will Deacon <will.deacon at arm.com>
> ---
>  drivers/virtio/virtio_ring.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index ed9c9eeedfe5..06b91e29d1b7 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -159,6 +159,10 @@ static bool vring_use_dma_api(struct virtio_device
*vdev)
>  	if (xen_domain())
>  		return true;
>  
> +	/* On ARM-based machines, the DMA ops will do the right thing */
> +	if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64))
> +		return true;
> +
>  	return false;
>  }
>  
> 
This patch makes my model usable again, so FWIW:

Acked-by: Marc Zyngier <marc.zyngier at arm.com>

	M.
-- 
Jazz is not dead. It just smells funny...

Jean-Philippe Brucker

2017-Jan-06 17:48 UTC

head link

[RFC PATCH] vring: Force use of DMA API for ARM-based systems

Hi Will,

On 20/12/16 15:14, Will Deacon wrote:> Booting Linux on an ARM fastmodel containing an SMMU emulation results
> in an unexpected I/O page fault from the legacy virtio-blk PCI device:
> 
> [    1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received:
> [    1.211800] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
> [    1.211880] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
> [    1.211959] arm-smmu-v3 2b400000.smmu:	0x00000008fa081002
> [    1.212075] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
> [    1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received:
> [    1.212234] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
> [    1.212314] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
> [    1.212394] arm-smmu-v3 2b400000.smmu:	0x00000008fa081000
> [    1.212471] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
> 
> <system hangs failing to read partition table>
> 
> This is because the virtio-blk is behind an SMMU, so we have consequently
> swizzled its DMA ops and configured the SMMU to translate accesses. This
> then requires the vring code to use the DMA API to establish translations,
> otherwise all transactions will result in fatal faults and termination.
> 
> Given that ARM-based systems only see an SMMU if one is really present
> (the topology is all described by firmware tables such as device-tree or
> IORT), then we can safely use the DMA API for all virtio devices.
There is a problem with the platform block device on that same model.
Since it's not behind the SMMU, the DMA ops fall back to swiotlb, which
limits the number of mappings.

It used to work with 4.9, but since 9491ae4 ("mm: don't cap request
size
based on read-ahead setting") unlocked read-ahead, we quickly run into
the limit of swiotlb and panic:

[    5.382359] virtio-mmio 1c130000.virtio_block: swiotlb buffer is full
(sz: 491520 bytes)
[    5.382452] virtio-mmio 1c130000.virtio_block: DMA: Out of SW-IOMMU
space for 491520 bytes
[    5.382531] Kernel panic - not syncing: DMA: Random memory could be
DMA written
...
[    5.383148] [<ffff0000083ad754>] swiotlb_map_page+0x194/0x1a0
[    5.383226] [<ffff000008096bb8>] __swiotlb_map_page+0x20/0x88
[    5.383320] [<ffff0000084bf738>] vring_map_one_sg.isra.1+0x70/0x88
[    5.383417] [<ffff0000084c04fc>] virtqueue_add_sgs+0x2ec/0x4e8
[    5.383505] [<ffff00000856d99c>] __virtblk_add_req+0x9c/0x1a8
...
[    5.384449] [<ffff0000081829c4>] ondemand_readahead+0xfc/0x2b8

Commit 9491ae4 caps the read-ahead request to a limit set by the backing
device. For virtio-blk, it is infinite (as set by the call to
blk_queue_max_hw_sectors in virtblk_probe).

I'm not sure how to fix this. Setting an arbitrary sector limit in the
virtio-blk driver seems unfair to other users. Maybe we should check if
the device is behind a hardware IOMMU before using the DMA API?

Thanks,
Jean-Philippe
> Cc: Andy Lutomirski <luto at kernel.org>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Will Deacon <will.deacon at arm.com>
> ---
>  drivers/virtio/virtio_ring.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index ed9c9eeedfe5..06b91e29d1b7 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -159,6 +159,10 @@ static bool vring_use_dma_api(struct virtio_device
*vdev)
>  	if (xen_domain())
>  		return true;
>  
> +	/* On ARM-based machines, the DMA ops will do the right thing */
> +	if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64))
> +		return true;
> +
>  	return false;
>  }
>  
>

Will Deacon

2017-Jan-06 18:08 UTC

head link

[RFC PATCH] vring: Force use of DMA API for ARM-based systems

Hi Jean-Philippe,

On Fri, Jan 06, 2017 at 05:48:33PM +0000, Jean-Philippe Brucker
wrote:> On 20/12/16 15:14, Will Deacon wrote:
> > Booting Linux on an ARM fastmodel containing an SMMU emulation results
> > in an unexpected I/O page fault from the legacy virtio-blk PCI device:
> > 
> > [    1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received:
> > [    1.211800] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
> > [    1.211880] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
> > [    1.211959] arm-smmu-v3 2b400000.smmu:	0x00000008fa081002
> > [    1.212075] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
> > [    1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received:
> > [    1.212234] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
> > [    1.212314] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
> > [    1.212394] arm-smmu-v3 2b400000.smmu:	0x00000008fa081000
> > [    1.212471] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
> > 
> > <system hangs failing to read partition table>
> > 
> > This is because the virtio-blk is behind an SMMU, so we have
consequently
> > swizzled its DMA ops and configured the SMMU to translate accesses.
This
> > then requires the vring code to use the DMA API to establish
translations,
> > otherwise all transactions will result in fatal faults and
termination.
> > 
> > Given that ARM-based systems only see an SMMU if one is really present
> > (the topology is all described by firmware tables such as device-tree
or
> > IORT), then we can safely use the DMA API for all virtio devices.
> 
> There is a problem with the platform block device on that same model.
> Since it's not behind the SMMU, the DMA ops fall back to swiotlb, which
> limits the number of mappings.
> 
> It used to work with 4.9, but since 9491ae4 ("mm: don't cap
request size
> based on read-ahead setting") unlocked read-ahead, we quickly run into
> the limit of swiotlb and panic:
> 
> [    5.382359] virtio-mmio 1c130000.virtio_block: swiotlb buffer is full
> (sz: 491520 bytes)
> [    5.382452] virtio-mmio 1c130000.virtio_block: DMA: Out of SW-IOMMU
> space for 491520 bytes
> [    5.382531] Kernel panic - not syncing: DMA: Random memory could be
> DMA written
> ...
> [    5.383148] [<ffff0000083ad754>] swiotlb_map_page+0x194/0x1a0
> [    5.383226] [<ffff000008096bb8>] __swiotlb_map_page+0x20/0x88
> [    5.383320] [<ffff0000084bf738>] vring_map_one_sg.isra.1+0x70/0x88
> [    5.383417] [<ffff0000084c04fc>] virtqueue_add_sgs+0x2ec/0x4e8
> [    5.383505] [<ffff00000856d99c>] __virtblk_add_req+0x9c/0x1a8
> ...
> [    5.384449] [<ffff0000081829c4>] ondemand_readahead+0xfc/0x2b8
Oh, lovely!
> Commit 9491ae4 caps the read-ahead request to a limit set by the backing
> device. For virtio-blk, it is infinite (as set by the call to
> blk_queue_max_hw_sectors in virtblk_probe).
> 
> I'm not sure how to fix this. Setting an arbitrary sector limit in the
> virtio-blk driver seems unfair to other users. Maybe we should check if
> the device is behind a hardware IOMMU before using the DMA API?
Couldn't the same issue potentially occur with a hardware IOMMU, where
we run out of IOVA space due to unlimited readahead? I think it might be
best to enforce a finite limit for virtio devices when the DMA API is in
use.

Do any drivers for physical (i.e. non-virtual) hardware make use of
unlimited readahead?

Will

Robin Murphy

2017-Jan-06 18:32 UTC

head link

[RFC PATCH] vring: Force use of DMA API for ARM-based systems

On 06/01/17 17:48, Jean-Philippe Brucker wrote:> Hi Will,
> 
> On 20/12/16 15:14, Will Deacon wrote:
>> Booting Linux on an ARM fastmodel containing an SMMU emulation results
>> in an unexpected I/O page fault from the legacy virtio-blk PCI device:
>>
>> [    1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received:
>> [    1.211800] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
>> [    1.211880] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
>> [    1.211959] arm-smmu-v3 2b400000.smmu:	0x00000008fa081002
>> [    1.212075] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
>> [    1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received:
>> [    1.212234] arm-smmu-v3 2b400000.smmu:	0x00000000fffff010
>> [    1.212314] arm-smmu-v3 2b400000.smmu:	0x0000020800000000
>> [    1.212394] arm-smmu-v3 2b400000.smmu:	0x00000008fa081000
>> [    1.212471] arm-smmu-v3 2b400000.smmu:	0x0000000000000000
>>
>> <system hangs failing to read partition table>
>>
>> This is because the virtio-blk is behind an SMMU, so we have
consequently
>> swizzled its DMA ops and configured the SMMU to translate accesses.
This
>> then requires the vring code to use the DMA API to establish
translations,
>> otherwise all transactions will result in fatal faults and termination.
>>
>> Given that ARM-based systems only see an SMMU if one is really present
>> (the topology is all described by firmware tables such as device-tree
or
>> IORT), then we can safely use the DMA API for all virtio devices.
> 
> There is a problem with the platform block device on that same model.
> Since it's not behind the SMMU, the DMA ops fall back to swiotlb, which
> limits the number of mappings.
> 
> It used to work with 4.9, but since 9491ae4 ("mm: don't cap
request size
> based on read-ahead setting") unlocked read-ahead, we quickly run into
> the limit of swiotlb and panic:
> 
> [    5.382359] virtio-mmio 1c130000.virtio_block: swiotlb buffer is full
> (sz: 491520 bytes)
> [    5.382452] virtio-mmio 1c130000.virtio_block: DMA: Out of SW-IOMMU
> space for 491520 bytes
> [    5.382531] Kernel panic - not syncing: DMA: Random memory could be
> DMA written
> ...
> [    5.383148] [<ffff0000083ad754>] swiotlb_map_page+0x194/0x1a0
> [    5.383226] [<ffff000008096bb8>] __swiotlb_map_page+0x20/0x88
> [    5.383320] [<ffff0000084bf738>] vring_map_one_sg.isra.1+0x70/0x88
> [    5.383417] [<ffff0000084c04fc>] virtqueue_add_sgs+0x2ec/0x4e8
> [    5.383505] [<ffff00000856d99c>] __virtblk_add_req+0x9c/0x1a8
> ...
> [    5.384449] [<ffff0000081829c4>] ondemand_readahead+0xfc/0x2b8
> 
> Commit 9491ae4 caps the read-ahead request to a limit set by the backing
> device. For virtio-blk, it is infinite (as set by the call to
> blk_queue_max_hw_sectors in virtblk_probe).
> 
> I'm not sure how to fix this. Setting an arbitrary sector limit in the
> virtio-blk driver seems unfair to other users. Maybe we should check if
> the device is behind a hardware IOMMU before using the DMA API?
Hmm, this looks more like the virtio_block device simply has the wrong
DMA mask to begin with. For virtio-pci we set the streaming DMA mask to
64 bits - should a platform device not be similarly capable?

Robin.
> 
> Thanks,
> Jean-Philippe
> 
>> Cc: Andy Lutomirski <luto at kernel.org>
>> Cc: Michael S. Tsirkin <mst at redhat.com>
>> Signed-off-by: Will Deacon <will.deacon at arm.com>
>> ---
>>  drivers/virtio/virtio_ring.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/virtio/virtio_ring.c
b/drivers/virtio/virtio_ring.c
>> index ed9c9eeedfe5..06b91e29d1b7 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -159,6 +159,10 @@ static bool vring_use_dma_api(struct virtio_device
*vdev)
>>  	if (xen_domain())
>>  		return true;
>>  
>> +	/* On ARM-based machines, the DMA ops will do the right thing */
>> +	if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64))
>> +		return true;
>> +
>>  	return false;
>>  }
>>  
>>
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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