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    Subject[PATCH 4.19 070/118] iommu/arm-smmu-v3: Dont disable SMMU in kdump kernel
    Date
    [ Upstream commit 3f54c447df34ff9efac7809a4a80fd3208efc619 ]

    Disabling the SMMU when probing from within a kdump kernel so that all
    incoming transactions are terminated can prevent the core of the crashed
    kernel from being transferred off the machine if all I/O devices are
    behind the SMMU.

    Instead, continue to probe the SMMU after it is disabled so that we can
    reinitialise it entirely and re-attach the DMA masters as they are reset.
    Since the kdump kernel may not have drivers for all of the active DMA
    masters, we suppress fault reporting to avoid spamming the console and
    swamping the IRQ threads.

    Reported-by: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
    Tested-by: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
    Tested-by: Bhupesh Sharma <bhsharma@redhat.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/iommu/arm-smmu-v3.c | 10 ++++------
    1 file changed, 4 insertions(+), 6 deletions(-)

    diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
    index 9ae3678844eb..40fbf20d69e5 100644
    --- a/drivers/iommu/arm-smmu-v3.c
    +++ b/drivers/iommu/arm-smmu-v3.c
    @@ -2414,13 +2414,9 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu, bool bypass)
    /* Clear CR0 and sync (disables SMMU and queue processing) */
    reg = readl_relaxed(smmu->base + ARM_SMMU_CR0);
    if (reg & CR0_SMMUEN) {
    - if (is_kdump_kernel()) {
    - arm_smmu_update_gbpa(smmu, GBPA_ABORT, 0);
    - arm_smmu_device_disable(smmu);
    - return -EBUSY;
    - }
    -
    dev_warn(smmu->dev, "SMMU currently enabled! Resetting...\n");
    + WARN_ON(is_kdump_kernel() && !disable_bypass);
    + arm_smmu_update_gbpa(smmu, GBPA_ABORT, 0);
    }

    ret = arm_smmu_device_disable(smmu);
    @@ -2513,6 +2509,8 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu, bool bypass)
    return ret;
    }

    + if (is_kdump_kernel())
    + enables &= ~(CR0_EVTQEN | CR0_PRIQEN);

    /* Enable the SMMU interface, or ensure bypass */
    if (!bypass || disable_bypass) {
    --
    2.20.1


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