Re: [RFC PATCH 2/4] PCI: Add "pci=iommu_passthrough=" parameter for iommu passthrough

Bjorn Helgaas
2020-01-21T14:17:22Z

[+cc linux-pci, thread at https://lore.kernel.org/r/20200101052648.14295-1-baolu.lu@linux.intel.com]

On Wed, Jan 01, 2020 at 01:26:46PM +0800, Lu Baolu wrote:
> The new parameter takes a list of devices separated by a semicolon.
> Each device specified will have its iommu_passthrough bit in struct
> device set. This is very similar to the existing 'disable_acs_redir'
> parameter.

Almost all of this patchset is in drivers/iommu. Should the parameter
be "iommu ..." instead of "pci=iommu_passthrough=..."?

There is already an "iommu.passthrough=" argument. Would this fit
better there? Since the iommu_passthrough bit is generic, it seems
like you anticipate similar situations for non-PCI devices.

> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
> .../admin-guide/kernel-parameters.txt | 5 +++
> drivers/pci/pci.c | 34 +++++++++++++++++++
> drivers/pci/pci.h | 1 +
> drivers/pci/probe.c | 2 ++
> 4 files changed, 42 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index ade4e6ec23e0..d3edc2cb6696 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3583,6 +3583,11 @@
> may put more devices in an IOMMU group.
> force_floating [S390] Force usage of floating interrupts.
> nomio [S390] Do not use MIO instructions.
> + iommu_passthrough=<pci_dev>[; ...]
> + Specify one or more PCI devices (in the format
> + specified above) separated by semicolons.
> + Each device specified will bypass IOMMU DMA
> + translation.
>
> pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
> Management.
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 90dbd7c70371..05bf3f4acc36 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6401,6 +6401,37 @@ void __weak pci_fixup_cardbus(struct pci_bus *bus)
> }
> EXPORT_SYMBOL(pci_fixup_cardbus);
>
> +static const char *iommu_passthrough_param;
> +bool pci_iommu_passthrough_match(struct pci_dev *dev)
> +{
> + int ret = 0;
> + const char *p = iommu_passthrough_param;
> +
> + if (!p)
> + return false;
> +
> + while (*p) {
> + ret = pci_dev_str_match(dev, p, &p);
> + if (ret < 0) {
> + pr_info_once("PCI: Can't parse iommu_passthrough parameter: %s\n",
> + iommu_passthrough_param);
> +
> + break;
> + } else if (ret == 1) {
> + pci_info(dev, "PCI: IOMMU passthrough\n");
> + return true;
> + }
> +
> + if (*p != ';' && *p != ',') {
> + /* End of param or invalid format */
> + break;
> + }
> + p++;
> + }
> +
> + return false;
> +}
> +
> static int __init pci_setup(char *str)
> {
> while (str) {
> @@ -6462,6 +6493,8 @@ static int __init pci_setup(char *str)
> pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
> } else if (!strncmp(str, "disable_acs_redir=", 18)) {
> disable_acs_redir_param = str + 18;
> + } else if (!strncmp(str, "iommu_passthrough=", 18)) {
> + iommu_passthrough_param = str + 18;
> } else {
> pr_err("PCI: Unknown option `%s'\n", str);
> }
> @@ -6486,6 +6519,7 @@ static int __init pci_realloc_setup_params(void)
> resource_alignment_param = kstrdup(resource_alignment_param,
> GFP_KERNEL);
> disable_acs_redir_param = kstrdup(disable_acs_redir_param, GFP_KERNEL);
> + iommu_passthrough_param = kstrdup(iommu_passthrough_param, GFP_KERNEL);
>
> return 0;
> }
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index a0a53bd05a0b..95f6af06aba6 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -288,6 +288,7 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev);
> void pci_disable_bridge_window(struct pci_dev *dev);
> struct pci_bus *pci_bus_get(struct pci_bus *bus);
> void pci_bus_put(struct pci_bus *bus);
> +bool pci_iommu_passthrough_match(struct pci_dev *dev);
>
> /* PCIe link information */
> #define PCIE_SPEED2STR(speed) \
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 512cb4312ddd..4c571ee75621 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2404,6 +2404,8 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
>
> dev->state_saved = false;
>
> + dev->dev.iommu_passthrough = pci_iommu_passthrough_match(dev);
> +
> pci_init_capabilities(dev);
>
> /*
> --
> 2.17.1