Hi Jean
On 6/29/22 11:14, Jean-Philippe Brucker wrote:
> 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).
Yes that's what I saw too
> 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?
sure
>
>> ---
>> 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.
OK
>
>> +}
>> +
>> /**
>> * 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
OK
Thanks
Eric
>
> Thanks,
> Jean
>
>
>> static inline int viot_iommu_configure(struct device *dev)
>> {
>> return -ENODEV;
>> --
>> 2.35.3
>>
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