From d80f6de9d601c30b53c17f00cb7cfe3169f2ddad Mon Sep 17 00:00:00 2001
From: Alexey Kardashevskiy <aik@ozlabs.ru>
Date: Thu, 14 Jul 2022 18:11:19 +1000
Subject: [PATCH] powerpc/iommu: Fix iommu_table_in_use for a small default DMA
window case
References: bsc#1212091 ltc#199106
Patch-mainline: v6.0-rc1
Git-commit: d80f6de9d601c30b53c17f00cb7cfe3169f2ddad
The existing iommu_table_in_use() helper checks if the kernel is using
any of TCEs. There are some reserved TCEs:
1) the very first one if DMA window starts from 0 to avoid having a zero
but still valid DMA handle;
2) it_reserved_start..it_reserved_end to exclude MMIO32 window in case
the default window spans across that - this is the default for the first
DMA window on PowerNV.
When 1) is the case and 2) is not the helper does not skip 1) and returns
wrong status.
This only seems occurring when passing through a PCI device to a nested
guest (not something we support really well) so it has not been seen
before.
This fixes the bug by adding a special case for no MMIO32 reservation.
Fixes: 3c33066a2190 ("powerpc/kernel/iommu: Add new iommu_table_in_use() helper")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220714081119.3714605-1-aik@ozlabs.ru
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kernel/iommu.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index 7e56ddb3e0b9..caebe1431596 100644
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -775,6 +775,11 @@ bool iommu_table_in_use(struct iommu_table *tbl)
/* ignore reserved bit0 */
if (tbl->it_offset == 0)
start = 1;
+
+ /* Simple case with no reserved MMIO32 region */
+ if (!tbl->it_reserved_start && !tbl->it_reserved_end)
+ return find_next_bit(tbl->it_map, tbl->it_size, start) != tbl->it_size;
+
end = tbl->it_reserved_start - tbl->it_offset;
if (find_next_bit(tbl->it_map, end, start) != end)
return true;
--
2.41.0