xen: privcmd: Add support for ioeventfd

Virtio guests send VIRTIO_MMIO_QUEUE_NOTIFY notification when they need
to notify the backend of an update to the status of the virtqueue. The
backend or another entity, polls the MMIO address for updates to know
when the notification is sent.

It works well if the backend does this polling by itself. But as we move
towards generic backend implementations, we end up implementing this in
a separate user-space program.

Generally, the Virtio backends are implemented to work with the Eventfd
based mechanism. In order to make such backends work with Xen, another
software layer needs to do the polling and send an event via eventfd to
the backend once the notification from guest is received. This results
in an extra context switch.

This is not a new problem in Linux though. It is present with other
hypervisors like KVM, etc. as well. The generic solution implemented in
the kernel for them is to provide an IOCTL call to pass the address to
poll and eventfd, which lets the kernel take care of polling and raise
an event on the eventfd, instead of handling this in user space (which
involves an extra context switch).

This patch adds similar support for xen.

Inspired by existing implementations for KVM, etc..

This also copies ioreq.h header file (only struct ioreq and related
macros) from Xen's source tree (Top commit 5d84f07fe6bf ("xen/pci: drop
remaining uses of bool_t")).

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/b20d83efba6453037d0c099912813c79c81f7714.1697439990.git.viresh.kumar@linaro.org
Signed-off-by: Juergen Gross <jgross@suse.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/include/xen/interface/hvm/ioreq.h b/include/xen/interface/hvm/ioreq.h
new file mode 100644
index 000000000000..b02cfeae7eb5
--- /dev/null
+++ b/include/xen/interface/hvm/ioreq.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * ioreq.h: I/O request definitions for device models
+ * Copyright (c) 2004, Intel Corporation.
+ */
+
+#ifndef __XEN_PUBLIC_HVM_IOREQ_H__
+#define __XEN_PUBLIC_HVM_IOREQ_H__
+
+#define IOREQ_READ      1
+#define IOREQ_WRITE     0
+
+#define STATE_IOREQ_NONE        0
+#define STATE_IOREQ_READY       1
+#define STATE_IOREQ_INPROCESS   2
+#define STATE_IORESP_READY      3
+
+#define IOREQ_TYPE_PIO          0 /* pio */
+#define IOREQ_TYPE_COPY         1 /* mmio ops */
+#define IOREQ_TYPE_PCI_CONFIG   2
+#define IOREQ_TYPE_TIMEOFFSET   7
+#define IOREQ_TYPE_INVALIDATE   8 /* mapcache */
+
+/*
+ * VMExit dispatcher should cooperate with instruction decoder to
+ * prepare this structure and notify service OS and DM by sending
+ * virq.
+ *
+ * For I/O type IOREQ_TYPE_PCI_CONFIG, the physical address is formatted
+ * as follows:
+ *
+ * 63....48|47..40|39..35|34..32|31........0
+ * SEGMENT |BUS   |DEV   |FN    |OFFSET
+ */
+struct ioreq {
+	uint64_t addr;          /* physical address */
+	uint64_t data;          /* data (or paddr of data) */
+	uint32_t count;         /* for rep prefixes */
+	uint32_t size;          /* size in bytes */
+	uint32_t vp_eport;      /* evtchn for notifications to/from device model */
+	uint16_t _pad0;
+	uint8_t state:4;
+	uint8_t data_is_ptr:1;  /* if 1, data above is the guest paddr
+				 * of the real data to use. */
+	uint8_t dir:1;          /* 1=read, 0=write */
+	uint8_t df:1;
+	uint8_t _pad1:1;
+	uint8_t type;           /* I/O type */
+};
+
+#endif /* __XEN_PUBLIC_HVM_IOREQ_H__ */