Hi Eric,
On Mon, Jun 27, 2022 at 02:55:34PM +0200, Eric Auger wrote:
> Currently acpi_viot_init() gets called after the pci
> device has been scanned and pci_enable_acs() has been called.
> So pci_request_acs() fails to be taken into account leading
> to wrong single iommu group topologies when dealing with
> multi-function root ports for instance.
>
> We cannot simply move the acpi_viot_init() earlier, similarly
> as the IORT init because the VIOT parsing relies on the pci
> scan. However we can detect VIOT is present earlier and in
> such a case, request ACS. Introduce a new acpi_viot_early_init()
> routine that allows to call pci_request_acs() before the scan.
>
> Fixes: 3cf485540e7b ("ACPI: Add driver for the VIOT table")
> Signed-off-by: Eric Auger <eric.au...@redhat.com>
> Reported-by: Jin Liu <j...@redhat.com>
Thanks for the fix, the patch makes sense and fixes the issue.
I wondered whether we should keep the logic where we only request ACS if
an IOMMU is found to manage a PCI range, but I can't see any harm in
requesting it regardless (plus there is a precedent with AMD IOMMU).
I could imagine some VMM wanting to only put an IOMMU in front of its MMIO
devices and leave PCI to roam free, but that seems like a stretch.
There is another issue with the existing code, though: we can't call
pci_request_acs() when CONFIG_PCI is disabled because no stub is defined.
Could you wrap the call in an #ifdef?
> ---
> drivers/acpi/bus.c | 1 +
> drivers/acpi/viot.c | 23 +++++++++++++++++------
> include/linux/acpi_viot.h | 2 ++
> 3 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> index 86fa61a21826..906ad8153fd9 100644
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -1400,6 +1400,7 @@ static int __init acpi_init(void)
>
> pci_mmcfg_late_init();
> acpi_iort_init();
> + acpi_viot_early_init();
> acpi_hest_init();
> acpi_ghes_init();
> acpi_scan_init();
> diff --git a/drivers/acpi/viot.c b/drivers/acpi/viot.c
> index d2256326c73a..3c1be123e4d6 100644
> --- a/drivers/acpi/viot.c
> +++ b/drivers/acpi/viot.c
> @@ -248,6 +248,23 @@ static int __init viot_parse_node(const struct
> acpi_viot_header *hdr)
> return ret;
> }
>
> +/**
> + * acpi_viot_early_init - Test the presence of VIOT and enable ACS
> + *
> + * If the VIOT does exist, ACS must be enabled. This cannot be
> + * done in acpi_viot_init() which is called after the bus scan
> + */
> +void __init acpi_viot_early_init(void)
> +{
> + acpi_status status;
> + struct acpi_table_header *hdr;
> +
> + status = acpi_get_table(ACPI_SIG_VIOT, 0, &hdr);
> + if (!ACPI_FAILURE(status))
> + pci_request_acs();
> + acpi_put_table(hdr);
I'd rather not call acpi_put_table() in case of failure. I know it is
handled but it looks fragile and I couldn't find any other user of
acpi_get_table() doing this.
> +}
> +
> /**
> * acpi_viot_init - Parse the VIOT table
> *
> @@ -319,12 +336,6 @@ static int viot_pci_dev_iommu_init(struct pci_dev *pdev,
> u16 dev_id, void *data)
> epid = ((domain_nr - ep->segment_start) << 16) +
> dev_id - ep->bdf_start + ep->endpoint_id;
>
> - /*
> - * If we found a PCI range managed by the viommu, we're
> - * the one that has to request ACS.
> - */
> - pci_request_acs();
> -
> return viot_dev_iommu_init(&pdev->dev, ep->viommu,
> epid);
> }
> diff --git a/include/linux/acpi_viot.h b/include/linux/acpi_viot.h
> index 1eb8ee5b0e5f..e58d60f8ff2e 100644
> --- a/include/linux/acpi_viot.h
> +++ b/include/linux/acpi_viot.h
> @@ -6,10 +6,12 @@
> #include <linux/acpi.h>
>
> #ifdef CONFIG_ACPI_VIOT
> +void __init acpi_viot_early_init(void);
> void __init acpi_viot_init(void);
> int viot_iommu_configure(struct device *dev);
> #else
> static inline void acpi_viot_init(void) {}
> +static inline void acpi_viot_early_init(void) {}
nit: different declaration order
Thanks,
Jean
> static inline int viot_iommu_configure(struct device *dev)
> {
> return -ENODEV;
> --
> 2.35.3
>
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