On 8/9/19 10:22 AM, Joerg Roedel wrote:
> From: Joerg Roedel <jroe...@suse.de>
>
> Using Passthrough mode when SME is active causes certain
> devices to use the SWIOTLB bounce buffer. The bounce buffer
> code has an upper limit of 256kb for the size of DMA
> allocations, which is too small for certain devices and
> causes them to fail.
>
> With this patch we enable IOMMU by default when SME is
> active in the system, making the default configuration work
> for more systems than it does now.
>
> Users that don't want IOMMUs to be enabled still can disable
> them with kernel parameters.
>
> Signed-off-by: Joerg Roedel <jroe...@suse.de>
> ---
> drivers/iommu/iommu.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 62cae6db0970..fbe1aa51bce9 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -104,6 +104,12 @@ static int __init iommu_subsys_init(void)
> else
> iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>
> + if ((iommu_def_domain_type == IOMMU_DOMAIN_IDENTITY) &&
> + sme_active()) {
> + pr_info("SME detected - Disabling default IOMMU passthrough\n");
> + iommu_def_domain_type = IOMMU_DOMAIN_DMA;
Should this also clear the iommu_pass_through variable (the one set by the
iommu kernel parameter in arch/x86/kernel/pci-dma.c)?
I guess this is more applicable to the original patchset that created the
CONFIG_IOMMU_DEFAULT_PASSTHROUGH option, but should the default
passthrough support be modified so that you don't have to specify multiple
kernel parameters to change it?
Right now, if CONFIG_IOMMU_DEFAULT_PASSTHROUGH is set to yes, you can't
just specify iommu=nopt to enable the IOMMU. You have to also specify
iommu.passthrough=0. Do we want to fix that so that just specifying
iommu=nopt or iommu.passthrough=0 does what is needed?
Thanks,
Tom
> + }
> +
> pr_info("Default domain type: %s\n",
> iommu_domain_type_str(iommu_def_domain_type));
>
>
