[ fixed Will's address... ]
On 2020-05-05 4:59 pm, Prabhakar Kushwaha wrote:
An SMMU Stream table is created by the primary kernel. This table is
used by the SMMU to perform address translations for device-originated
transactions. Any crash (if happened) launches the kdump kernel which
re-creates the SMMU Stream table. New transactions will be translated
via this new table.
There are scenarios, where devices are still having old pending
transactions (configured in the primary kernel). These transactions
come in-between Stream table creation and device-driver probe.
As new stream table does not have entry for older transactions,
it will be aborted by SMMU.
Similar observations were found with PCIe-Intel 82576 Gigabit
Network card. It sends old Memory Read transaction in kdump kernel.
Transactions configured for older Stream table entries, that do not
exist any longer in the new table, will cause a PCIe Completion Abort.
Returned PCIe completion abort further leads to AER Errors from APEI
Generic Hardware Error Source (GHES) with completion timeout.
A network device hang is observed even after continuous
reset/recovery from driver, Hence device is no more usable.
So, If we are in a kdump kernel try to copy SMMU Stream table from
primary/old kernel to preserve the mappings until the device driver
takes over.
What about the context descriptors and pagetables that the old stream
table points to - can you trust that those are still present and correct
and not going to kill your device?
Signed-off-by: Prabhakar Kushwaha <pkushwaha@xxxxxxxxxxx>
---
This patch has been tested with
A) PCIe-Intel 82576 Gigabit Network card in following
configurations with "no AER error". Each iteration has
been tested on both Suse kdump rfs And default Centos distro rfs.
1) with 2 level stream table
----------------------------------------------------
SMMU | Normal Ping | Flood Ping
-----------------------------------------------------
Default Operation | 100 times | 10 times
-----------------------------------------------------
IOMMU bypass | 41 times | 10 times
-----------------------------------------------------
2) with Linear stream table.
-----------------------------------------------------
SMMU | Normal Ping | Flood Ping
------------------------------------------------------
Default Operation | 100 times | 10 times
------------------------------------------------------
IOMMU bypass | 55 times | 10 times
-------------------------------------------------------
B) This patch is also tested with Micron Technology Inc 9200 PRO NVMe
SSD card with 2 level stream table using "fio" in mixed read/write and
only read configurations. It is tested for both Default Operation and
IOMMU bypass mode for minimum 10 iterations across Centos kdump rfs and
default Centos ditstro rfs.
This patch is not full proof solution. Issue can still come
from the point device is discovered and driver probe called.
This patch has reduced window of scenario from "SMMU Stream table
creation - device-driver" to "device discovery - device-driver".
Usually, device discovery to device-driver is very small time. So
the probability is very low.
Note: device-discovery will overwrite existing stream table entries
with both SMMU stage as by-pass.
...which if there *is* ongoing DMA to addresses from previous virtual
mappings, stands just as much chance of killing the device and/or
corrupting the kdump kernel when it starts hitting random bits of the
physical address map.
drivers/iommu/arm-smmu-v3.c | 36 +++++++++++++++++++++++++++++++++++-
1 file changed, 35 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 82508730feb7..64d1b925932d 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1847,7 +1847,13 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
break;
case STRTAB_STE_0_CFG_S1_TRANS:
case STRTAB_STE_0_CFG_S2_TRANS:
- ste_live = true;
+ /*
+ * As kdump kernel copy STE table from previous
+ * kernel. It still may have valid stream table entries.
+ * Forcing entry as false to allow overwrite.
+ */
+ if (!is_kdump_kernel())
+ ste_live = true;
break;
case STRTAB_STE_0_CFG_ABORT:
BUG_ON(!disable_bypass);
@@ -3264,6 +3270,9 @@ static int arm_smmu_init_l1_strtab(struct arm_smmu_device *smmu)
return -ENOMEM;
}
+ if (is_kdump_kernel())
+ return 0;
+
for (i = 0; i < cfg->num_l1_ents; ++i) {
arm_smmu_write_strtab_l1_desc(strtab, &cfg->l1_desc[i]);
strtab += STRTAB_L1_DESC_DWORDS << 3;
@@ -3272,6 +3281,23 @@ static int arm_smmu_init_l1_strtab(struct arm_smmu_device *smmu)
return 0;
}
+static void arm_smmu_copy_table(struct arm_smmu_device *smmu,
+ struct arm_smmu_strtab_cfg *cfg, u32 size)
+{
+ struct arm_smmu_strtab_cfg rdcfg;
+
+ rdcfg.strtab_dma = readq_relaxed(smmu->base + ARM_SMMU_STRTAB_BASE);
+ rdcfg.strtab_base_cfg = readq_relaxed(smmu->base
+ + ARM_SMMU_STRTAB_BASE_CFG);
+
+ rdcfg.strtab_dma &= STRTAB_BASE_ADDR_MASK;
+ rdcfg.strtab = ioremap(rdcfg.strtab_dma, size);
ioremap? The old table is probably in RAM and previously mapped with
some Normal memory attribute, and may well be cached. This pretty much
guarantees mismatched attributes, at which point who knows what you'll
actually read?
Frankly, I'm going to say we already support a way to completely
preserve the previous SMMU configuration in a kdump kernel if users
really want to. Can you guess what that is?
Robin.
+ memcpy_fromio(cfg->strtab, rdcfg.strtab, size);
+
+ cfg->strtab_base_cfg = rdcfg.strtab_base_cfg;
+}
+
static int arm_smmu_init_strtab_2lvl(struct arm_smmu_device *smmu)
{
void *strtab;
@@ -3307,6 +3333,9 @@ static int arm_smmu_init_strtab_2lvl(struct arm_smmu_device *smmu)
reg |= FIELD_PREP(STRTAB_BASE_CFG_SPLIT, STRTAB_SPLIT);
cfg->strtab_base_cfg = reg;
+ if (is_kdump_kernel())
+ arm_smmu_copy_table(smmu, cfg, l1size);
+
return arm_smmu_init_l1_strtab(smmu);
}
@@ -3334,6 +3363,11 @@ static int arm_smmu_init_strtab_linear(struct arm_smmu_device *smmu)
reg |= FIELD_PREP(STRTAB_BASE_CFG_LOG2SIZE, smmu->sid_bits);
cfg->strtab_base_cfg = reg;
+ if (is_kdump_kernel()) {
+ arm_smmu_copy_table(smmu, cfg, size);
+ return 0;
+ }
+
arm_smmu_init_bypass_stes(strtab, cfg->num_l1_ents);
return 0;
}
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