RE: [PATCH rc v4 2/5] iommu/arm-smmu-v3: Implement is_attach_deferred() for kdump

RE: [PATCH rc v4 2/5] iommu/arm-smmu-v3: Implement is_attach_deferred() for kdump

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@nvidia.com>
> Sent: Wednesday, April 29, 2026 3:21 PM
> 
> Though the kdump kernel adopts the crashed kernel's stream table, the
> iommu
> core will still try to attach each probed device to a default domain, which
> overwrites the adopted STE and breaks in-flight DMA from that device.
> 
> Implement an is_attach_deferred() callback to prevent this. For each device
> that has STE.V=1 and STE.Cfg!=Abort in the adopted table, defer the default
> domain attachment, until the device driver explicitly requests it.
> 
> Fixes: b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions if SMMU
> is enabled in kdump kernel")
> Cc: stable@vger.kernel.org # v6.12+
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

RE: [PATCH rc v4 3/5] iommu/arm-smmu-v3: Skip EVTQ/PRIQ setup in kdump kernel

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@nvidia.com>
> Sent: Wednesday, April 29, 2026 3:21 PM
> 
> In kdump cases, the crashed kernel's CDs and page tables can be corrupted,
> which could trigger event spamming. Also, we cannot serve page requests.
> 
> Skip the EVTQ/PRIQ setup entirely rather than enabling then disabling them.

this is a refactoring to achieve the same goal as before...

> 
> Skip the IRQ setup and guard their thread functions as well.

... while this sounds a new enforcement (then better in a separate patch?)

> 
> Also add some inline comments explaining that.
> 
> Fixes: b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions if SMMU
> is enabled in kdump kernel")
> Cc: stable@vger.kernel.org # v6.12+
> Suggested-by: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Overall it looks good:

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

RE: [PATCH rc v4 4/5] iommu/arm-smmu-v3: Retain CR0_SMMUEN during kdump device reset

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@nvidia.com>
> Sent: Wednesday, April 29, 2026 3:21 PM
> 
> When ARM_SMMU_OPT_KDUMP_ADOPT is detected, do not disable
> SMMUEN and skip
> the CR1/CR2/STRTAB_BASE update sequence in arm_smmu_device_reset().
> Those
> register writes are all CONSTRAINED UNPREDICTABLE while
> CR0_SMMUEN==1, so
> leaving them intact lets in-flight DMAs continue to be translated by the
> adopted stream table.
> 
> Initialize 'enables' to 0 so it can carry CR0_SMMUEN in kdump case. Then,
> preserve that when enabling the command queue.
> 
> Clear latched gerror bits if necessary.
> 
> Fixes: b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions if SMMU
> is enabled in kdump kernel")
> Cc: stable@vger.kernel.org # v6.12+
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

RE: [PATCH rc v4 5/5] iommu/arm-smmu-v3: Detect ARM_SMMU_OPT_KDUMP_ADOPT in probe()

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@nvidia.com>
> Sent: Wednesday, April 29, 2026 3:21 PM
> 
> arm_smmu_device_hw_probe() runs before arm_smmu_init_structures(), so
> it's
> natural to decide whether the kdump kernel must adopt the crashed kernel's
> stream table.
> 
> Given that memremap is used to adopt the old stream table, set this option
> only on a coherent SMMU.
> 
> And make sure SMMU isn't in Service Failure Mode.
> 
> Fixes: b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions if SMMU
> is enabled in kdump kernel")
> Cc: stable@vger.kernel.org # v6.12+
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>, with nits:

> 
> +static void arm_smmu_device_hw_probe_kdump(struct arm_smmu_device
> *smmu)
> +{
> +	u32 gerror, gerrorn, active;
> +
> +	/*
> +	 * If SMMU is already active in kdump case, there could be in-flight
> DMA
> +	 * from devices initiated by the crashed kernel.
> +	 */
> +	if (!(readl_relaxed(smmu->base + ARM_SMMU_CR0) &
> CR0_SMMUEN))
> +		return;

Above comment is for the entire function. for the check here the comment
should be that no in-fly DMA to require adoption due to SMMU disabled.

> +
> +	/* For now, only support a coherent SMMU that works with
> MEMREMAP_WB */
> +	if (!(smmu->features & ARM_SMMU_FEAT_COHERENCY)) {
> +		dev_warn(smmu->dev,
> +			 "kdump: non-coherent SMMU can't adopt stream
> table\n");

"can't adopt stream table so SMMU will be reset to block all DMAs"

Re: [PATCH rc v4 3/5] iommu/arm-smmu-v3: Skip EVTQ/PRIQ setup in kdump kernel

[Nicolin Chen]

On Fri, May 08, 2026 at 07:41:20AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: Wednesday, April 29, 2026 3:21 PM
> > 
> > In kdump cases, the crashed kernel's CDs and page tables can be corrupted,
> > which could trigger event spamming. Also, we cannot serve page requests.
> > 
> > Skip the EVTQ/PRIQ setup entirely rather than enabling then disabling them.
> 
> this is a refactoring to achieve the same goal as before...
> 
> > 
> > Skip the IRQ setup and guard their thread functions as well.
> 
> ... while this sounds a new enforcement (then better in a separate patch?)

In v5, I split it into two patches and kept your Reviewed-by:
 - iommu/arm-smmu-v3: Skip EVTQ/PRIQ setup in kdump kernel
 - iommu/arm-smmu-v3: Suppress EVTQ/PRIQ events in kdump kernel

Thanks
Nicolin

Re: [PATCH rc v4 5/5] iommu/arm-smmu-v3: Detect ARM_SMMU_OPT_KDUMP_ADOPT in probe()

[Nicolin Chen]

On Fri, May 08, 2026 at 07:47:22AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > +	/*
> > +	 * If SMMU is already active in kdump case, there could be in-flight
> > DMA
> > +	 * from devices initiated by the crashed kernel.
> > +	 */
> > +	if (!(readl_relaxed(smmu->base + ARM_SMMU_CR0) &
> > CR0_SMMUEN))
> > +		return;
> 
> Above comment is for the entire function. for the check here the comment
> should be that no in-fly DMA to require adoption due to SMMU disabled.

Changed it to:
	/* No adoption if SMMU is disabled (i.e., there is no in-flight DMA) */

> > +
> > +	/* For now, only support a coherent SMMU that works with
> > MEMREMAP_WB */
> > +	if (!(smmu->features & ARM_SMMU_FEAT_COHERENCY)) {
> > +		dev_warn(smmu->dev,
> > +			 "kdump: non-coherent SMMU can't adopt stream
> > table\n");
> 
> "can't adopt stream table so SMMU will be reset to block all DMAs"

That'd be a bit too long. So, I changed it to:
	"kdump: non-coherent SMMU unsupported; reset to block all DMAs\n");

Thanks
Nicolin