Re: [PATCH 4/4] vfio: vfio_iommu_type1: implement VFIO_IOMMU_INFO_CAPABILITIES

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On 16/05/2019 20:40, Alex Williamson wrote:
On Fri, 10 May 2019 10:22:35 +0200
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:

We implement a capability intercafe for VFIO_IOMMU_GET_INFO and add the
first capability: VFIO_IOMMU_INFO_CAPABILITIES.

When calling the ioctl, the user must specify
VFIO_IOMMU_INFO_CAPABILITIES to retrieve the capabilities and must check
in the answer if capabilities are supported.
Older kernel will not check nor set the VFIO_IOMMU_INFO_CAPABILITIES in
the flags of vfio_iommu_type1_info.

The iommu get_attr callback will be called to retrieve the specific
attributes and fill the capabilities, VFIO_IOMMU_INFO_CAP_QFN for the
PCI query function attributes and VFIO_IOMMU_INFO_CAP_QGRP for the
PCI query function group.

Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
---
  drivers/vfio/vfio_iommu_type1.c | 95 ++++++++++++++++++++++++++++++++++++++++-
  1 file changed, 94 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index d0f731c..f7f8120 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -1658,6 +1658,70 @@ static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
  	return ret;
  }
+int vfio_iommu_type1_caps(struct vfio_iommu *iommu, struct vfio_info_cap *caps,
+			  size_t size)
+{
+	struct vfio_domain *d;
+	struct vfio_iommu_type1_info_block *info_fn;
+	struct vfio_iommu_type1_info_block *info_grp;
+	unsigned long total_size, fn_size, grp_size;
+	int ret;
+
+	d = list_first_entry(&iommu->domain_list, struct vfio_domain, next);
+	if (!d)
+		return -ENODEV;
+	/* The size of these capabilities are device dependent */
+	fn_size = iommu_domain_get_attr(d->domain,
+					DOMAIN_ATTR_ZPCI_FN_SIZE, NULL);
+	if (fn_size < 0)
+		return fn_size;

What if non-Z archs want to use this?  The function is architected
specifically for this one use case, fail if any component is not there
which means it requires a re-write to add further support.  If
ZPCI_FN_SIZE isn't support, move on to the next thing.

yes, clear.


+	fn_size +=  sizeof(struct vfio_info_cap_header);
+	total_size = fn_size;

Here too, total_size should be initialized to zero and each section +=
the size they'd like to add.

thanks, clear too.


+
+	grp_size = iommu_domain_get_attr(d->domain,
+					 DOMAIN_ATTR_ZPCI_GRP_SIZE, NULL);
+	if (grp_size < 0)
+		return grp_size;
+	grp_size +=  sizeof(struct vfio_info_cap_header);
+	total_size += grp_size;
+
+	/* Tell caller to call us with a greater buffer */
+	if (total_size > size) {
+		caps->size = total_size;
+		return 0;
+	}
+
+	info_fn = kzalloc(fn_size, GFP_KERNEL);
+	if (!info_fn)
+		return -ENOMEM;

Maybe fn_size was zero because we're not on Z.

+	ret = iommu_domain_get_attr(d->domain,
+				    DOMAIN_ATTR_ZPCI_FN, &info_fn->data);

Kernel internal structures != user api.  Thanks,

Alex

Thanks a lot Alex,
I understand the concerns, I was too focussed on Z, I will rework this as you said:
- definition of the user API and
- take care that another architecture may want to use the interface.

Regards,
Pierre



--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany




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