On Fri, Feb 22, 2019 at 12:28:30PM +0100, Cédric Le Goater wrote:

These controls will be used by the H_INT_SET_QUEUE_CONFIG and
H_INT_GET_QUEUE_CONFIG hcalls from QEMU. They will also be used to
restore the configuration of the XIVE EQs in the KVM device and to
capture the internal runtime state of the EQs. Both 'get' and 'set'
rely on an OPAL call to access from the XIVE interrupt controller the
EQ toggle bit and EQ index which are updated by the HW when event
notifications are enqueued in the EQ.

The value of the guest physical address of the event queue is saved in
the XIVE internal xive_q structure for later use. That is when
migration needs to mark the EQ pages dirty to capture a consistent
memory state of the VM.

To be noted that H_INT_SET_QUEUE_CONFIG does not require the extra
OPAL call setting the EQ toggle bit and EQ index to configure the EQ,
but restoring the EQ state will.

[snip]

+/* Layout of 64-bit eq attribute */
+#define KVM_XIVE_EQ_PRIORITY_SHIFT	0
+#define KVM_XIVE_EQ_PRIORITY_MASK	0x7
+#define KVM_XIVE_EQ_SERVER_SHIFT	3
+#define KVM_XIVE_EQ_SERVER_MASK		0xfffffff8ULL
+
+/* Layout of 64-bit eq attribute values */
+struct kvm_ppc_xive_eq {
+	__u32 flags;
+	__u32 qsize;
+	__u64 qpage;
+	__u32 qtoggle;
+	__u32 qindex;
+	__u8  pad[40];
+};

This is confusing.  What's the difference between an "eq attribute"
and an "eq attribute value"?  Is the first actually a queue index or
a queue identifier?

Also, the kvm_ppc_xive_eq is not 64 bits, so the comment above it is
wrong.  Maybe you meant "64-byte"?

[snip]

+	page = gfn_to_page(kvm, gpa_to_gfn(kvm_eq.qpage));
+	if (is_error_page(page)) {
+		pr_warn("Couldn't get guest page for %llx!\n", kvm_eq.qpage);
+		return -ENOMEM;
+	}
+	qaddr = page_to_virt(page) + (kvm_eq.qpage & ~PAGE_MASK);

Isn't this assuming that we can map the whole queue with a single
gfn_to_page?  That would only be true if kvm_eq.qsize <= PAGE_SHIFT.
What happens if kvm_eq.qsize > PAGE_SHIFT?

Paul.