Re: BUG kernel 6.12.19 defautl_swiotlb_limit() returns wrong value for CONFIG_SWIOTLB_DYNAMIC=y effects atm only under XEN dom0

[James Dingwall <james@dingwall.me.uk>]

Hi,

I've been having a problem with a Dell HBA330 SCSI controller (mpt3sas)
when booting under Xen and CONFIG_SWIOTLB_DYNAMIC=y is set.  I had a
similar issue with a megaraid_sas card that I previously posted about:

https://lkml.iu.edu/hypermail/linux/kernel/2407.3/08254.html

In that case we rebuilt the kernel with CONFIG_SWIOTLB_DYNAMIC=n.
While investigating the current problem I came across a patch that was
posted on the xen-devel list:

https://lists.xen.org/archives/html/xen-devel/2025-05/msg00991.html

I have applied that to the Ubuntu 7.0.0-31 kernel sources which has
resolved the controller initialisation error I was encountering and the
system now boots as expected.

[    3.921136] mpt3sas_cm0: no suitable DMA mask for 0000:03:00.0
[    3.921275] mpt3sas_cm0: failure at drivers/scsi/mpt3sas/mpt3sas_scsih.c:13610/_scsih_probe()!

I've included the patch below, I don't have the author's real address
for the s-o-b.  I'm able to test alternative fixes if there are any
issues with this one.

Thanks,
James


Signed-off-by: Andreas Greve andreas.greve@xxxxxxxxxx
Tested-by: James Dingwall <james@dingwall.me.uk>

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index abcf3fa63a56..742e6cbbe852 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1654,7 +1654,16 @@ phys_addr_t default_swiotlb_base(void)
 phys_addr_t default_swiotlb_limit(void)
 {
 #ifdef CONFIG_SWIOTLB_DYNAMIC
-	return io_tlb_default_mem.phys_limit;
+	struct io_tlb_mem *mem = &io_tlb_default_mem;
+	phys_addr_t retval = mem->defpool.end;
+	struct io_tlb_pool *pool;
+	rcu_read_lock();
+	list_for_each_entry_rcu(pool, &mem->pools, node) {
+		if (pool->end > retval)
+			retval = pool->end;
+	}
+	rcu_read_unlock();
+	return retval - 1;
 #else
 	return io_tlb_default_mem.defpool.end - 1;
 #endif