Re: [PATCH v2] iommu/vt-d: Turn off translations at shutdown

[Lu Baolu]

Hi,

On 11/11/19 1:27 AM, Deepa Dinamani wrote:
> The intel-iommu driver assumes that the iommu state is
> cleaned up at the start of the new kernel.
> But, when we try to kexec boot something other than the
> Linux kernel, the cleanup cannot be relied upon.
> Hence, cleanup before we go down for reboot.
>
> Keeping the cleanup at initialization also, in case BIOS
> leaves the IOMMU enabled.

Do you mind shining more light on this statement? I can't get your point
here. Currently iommu_shutdown() only happens for reboot, right?

Best regards,
baolu

> I considered turning off iommu only during kexec reboot, but a clean
> shutdown seems always a good idea. But if someone wants to make it
> conditional, such as VMM live update, we can do that.  There doesn't
> seem to be such a condition at this time.
>
> Tested that before, the info message
> 'DMAR: Translation was enabled for <iommu> but we are not in kdump mode'
> would be reported for each iommu. The message will not appear when the
> DMA-remapping is not enabled on entry to the kernel.
>
> Signed-off-by: Deepa Dinamani <deepa.kernel@xxxxxxxxx>
> ---
> Changes since v1:
> * move shutdown registration to iommu detection
>
>   drivers/iommu/dmar.c        |  5 ++++-
>   drivers/iommu/intel-iommu.c | 20 ++++++++++++++++++++
>   include/linux/dmar.h        |  2 ++
>   3 files changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
> index eecd6a421667..3acfa6a25fa2 100644
> --- a/drivers/iommu/dmar.c
> +++ b/drivers/iommu/dmar.c
> @@ -895,8 +895,11 @@ int __init detect_intel_iommu(void)
>   	}
>   
>   #ifdef CONFIG_X86
> -	if (!ret)
> +	if (!ret) {
>   		x86_init.iommu.iommu_init = intel_iommu_init;
> +		x86_platform.iommu_shutdown = intel_iommu_shutdown;
> +	}
> +
>   #endif
>   
>   	if (dmar_tbl) {
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index fe8097078669..7ac73410ba8e 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -4764,6 +4764,26 @@ static void intel_disable_iommus(void)
>   		iommu_disable_translation(iommu);
>   }
>   
> +void intel_iommu_shutdown(void)
> +{
> +	struct dmar_drhd_unit *drhd;
> +	struct intel_iommu *iommu = NULL;
> +
> +	if (no_iommu || dmar_disabled)
> +		return;
> +
> +	down_write(&dmar_global_lock);
> +
> +	/* Disable PMRs explicitly here. */
> +	for_each_iommu(iommu, drhd)
> +		iommu_disable_protect_mem_regions(iommu);
> +
> +	/* Make sure the IOMMUs are switched off */
> +	intel_disable_iommus();
> +
> +	up_write(&dmar_global_lock);
> +}
> +
>   static inline struct intel_iommu *dev_to_intel_iommu(struct device *dev)
>   {
>   	struct iommu_device *iommu_dev = dev_to_iommu_device(dev);
> diff --git a/include/linux/dmar.h b/include/linux/dmar.h
> index a7cf3599d9a1..f64ca27dc210 100644
> --- a/include/linux/dmar.h
> +++ b/include/linux/dmar.h
> @@ -129,6 +129,7 @@ static inline int dmar_res_noop(struct acpi_dmar_header *hdr, void *arg)
>   #ifdef CONFIG_INTEL_IOMMU
>   extern int iommu_detected, no_iommu;
>   extern int intel_iommu_init(void);
> +extern void intel_iommu_shutdown(void);
>   extern int dmar_parse_one_rmrr(struct acpi_dmar_header *header, void *arg);
>   extern int dmar_parse_one_atsr(struct acpi_dmar_header *header, void *arg);
>   extern int dmar_check_one_atsr(struct acpi_dmar_header *hdr, void *arg);
> @@ -137,6 +138,7 @@ extern int dmar_iommu_hotplug(struct dmar_drhd_unit *dmaru, bool insert);
>   extern int dmar_iommu_notify_scope_dev(struct dmar_pci_notify_info *info);
>   #else /* !CONFIG_INTEL_IOMMU: */
>   static inline int intel_iommu_init(void) { return -ENODEV; }
> +static inline void intel_iommu_shutdown(void) { }
>   
>   #define	dmar_parse_one_rmrr		dmar_res_noop
>   #define	dmar_parse_one_atsr		dmar_res_noop