[PATCH 1/2] iommu/amd: Program device table when kdump reuse fails

[Matt Fleming <matt@readmodwrite.com>]

From: Matt Fleming <mfleming@cloudflare.com>

Commit 38e5f33ee359 ("iommu/amd: Reuse device table for kdump") made
iommu_set_device_table() return early in every kdump kernel. That is
needed when the previous kernel's device table is reused: the base
register already points at it, and on SNP-enabled systems the register
is locked.

But if reuse isn't possible, early_enable_iommus() falls back to the
freshly allocated table and calls early_enable_iommu(). Because of the
early return, that table is never written to the base register. The
IOMMU keeps using whatever table the register pointed at before, while
the driver writes entries into the new one.

Only skip the write when the previous kernel's table was reused.

Fixes: 38e5f33ee359 ("iommu/amd: Reuse device table for kdump")
Cc: stable@vger.kernel.org
Signed-off-by: Matt Fleming <mfleming@cloudflare.com>
---
 drivers/iommu/amd/init.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index c07c3a01b978..0572e1a674f0 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -409,7 +409,13 @@ static void iommu_set_device_table(struct amd_iommu *iommu)
 
 	BUG_ON(iommu->mmio_base == NULL);
 
-	if (is_kdump_kernel())
+	/*
+	 * A kdump kernel that reuses the previous kernel's device table must
+	 * leave the base register alone. It already points at that table, and
+	 * with SNP enabled the register is locked. If reuse failed, program
+	 * the freshly allocated table like a normal boot.
+	 */
+	if (iommu->pci_seg->old_dev_tbl_cpy)
 		return;
 
 	entry = iommu_virt_to_phys(dev_table);
-- 
2.43.0