Hello Randy,

Thanks for your quick review.

Randy Dunlap [off-list ref] writes:

On 08/24/2018 09:25 AM, Thiago Jung Bauermann wrote:

quoted

From: Anshuman Khandual <redacted>

SWIOTLB buffer default size (64MB) is not enough for large sequential write
operations which eventually leads to kernel crash like here.

virtio-pci 0000:00:05.0: swiotlb buffer is full (sz: 327680 bytes)
virtio-pci 0000:00:05.0: DMA: Out of SW-IOMMU space for 327680 bytes
Kernel panic - not syncing: DMA: Random memory could be DMA read
CPU: 12 PID: 3985 Comm: mkfs.ext4 Not tainted 4.18.0-rc4+ #285
Call Trace:
[c0000007d2a27020] [c000000000cfdffc] dump_stack+0xb0/0xf4 (unreliable)
[c0000007d2a27060] [c000000000112a98] panic+0x140/0x328
[c0000007d2a270f0] [c0000000001b4f88] swiotlb_full+0x108/0x130
[c0000007d2a27180] [c0000000001b5f6c] swiotlb_map_page+0x25c/0x2c0
[c0000007d2a271e0] [c0000000007bfaf8] vring_map_one_sg.isra.0+0x58/0x70
[c0000007d2a27200] [c0000000007c08dc] virtqueue_add_sgs+0x1bc/0x690
[c0000007d2a272f0] [d0000000042a1280] virtio_queue_rq+0x358/0x4a0 [virtio_blk]
[c0000007d2a273d0] [c0000000006b5d68] blk_mq_dispatch_rq_list+0x1f8/0x6d0
..................

Increase the SWIOTLB size to 1GB on Ultravisor based secure guests.

Signed-off-by: Anshuman Khandual <redacted>
Signed-off-by: Thiago Jung Bauermann <redacted>
---
 arch/powerpc/Kconfig | 5 +++++
 kernel/dma/swiotlb.c | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 1466d1234723..fee7194ce9e4 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -457,6 +457,11 @@ config PPC_SVM

 	 If unsure, say "N".

+config SWIOTLB_DEFAULT_SIZE
+       int "Size of Software I/O TLB buffer (in MiB)"
+       default "1024"

I would add a "range" to limit (restrict) how small or large that can be.  E.g.:

	range 16 102400

or even smaller for the maximum value...

That's an interesting idea. Since this config option is restricted to
PPC_SVM it may be possible to find out what reasonable limits would be.
I'll have to experiment a bit to find out. Though I can say that 16 MB
is too small since even with 64 MB the kernel panics with the simple
task of formatting a filesystem...

--
Thiago Jung Bauermann
IBM Linux Technology Center