[kvm-unit-tests PATCH v5 2/3] s390x: define UV compatible I/O allocation

From: Pierre Morel <pmorel@linux.ibm.com>
To: kvm@vger.kernel.org
Cc: linux-s390@vger.kernel.org, frankja@linux.ibm.com,
	david@redhat.com, thuth@redhat.com, cohuck@redhat.com,
	imbrenda@linux.ibm.com, drjones@redhat.com, pbonzini@redhat.com
Subject: [kvm-unit-tests PATCH v5 2/3] s390x: define UV compatible I/O allocation
Date: Fri, 22 Jan 2021 14:27:39 +0100	[thread overview]
Message-ID: <1611322060-1972-3-git-send-email-pmorel@linux.ibm.com> (raw)
In-Reply-To: <1611322060-1972-1-git-send-email-pmorel@linux.ibm.com>

To centralize the memory allocation for I/O we define
the alloc_io_mem/free_io_mem functions which share the I/O
memory with the host in case the guest runs with
protected virtualization.

These functions allocate on a page integral granularity to
ensure a dedicated sharing of the allocated objects.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
---
 lib/s390x/malloc_io.c | 71 +++++++++++++++++++++++++++++++++++++++++++
 lib/s390x/malloc_io.h | 45 +++++++++++++++++++++++++++
 s390x/Makefile        |  1 +
 3 files changed, 117 insertions(+)
 create mode 100644 lib/s390x/malloc_io.c
 create mode 100644 lib/s390x/malloc_io.h

diff --git a/lib/s390x/malloc_io.c b/lib/s390x/malloc_io.c
new file mode 100644
index 0000000..b01222e
--- /dev/null
+++ b/lib/s390x/malloc_io.c
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * I/O page allocation
+ *
+ * Copyright (c) 2021 IBM Corp
+ *
+ * Authors:
+ *  Pierre Morel <pmorel@linux.ibm.com>
+ *
+ * Using this interface provide host access to the allocated pages in
+ * case the guest is a secure guest.
+ * This is needed for I/O buffers.
+ *
+ */
+#include <libcflat.h>
+#include <asm/page.h>
+#include <asm/uv.h>
+#include <malloc_io.h>
+#include <alloc_page.h>
+#include <asm/facility.h>
+#include <bitops.h>
+
+static int share_pages(void *p, int count)
+{
+	int i = 0;
+
+	for (i = 0; i < count; i++, p += PAGE_SIZE)
+		if (uv_set_shared((unsigned long)p))
+			break;
+	return i;
+}
+
+static void unshare_pages(void *p, int count)
+{
+	int i;
+
+	for (i = count; i > 0; i--, p += PAGE_SIZE)
+		uv_remove_shared((unsigned long)p);
+}
+
+void *alloc_io_mem(int size, int flags)
+{
+	int order = get_order(size >> PAGE_SHIFT);
+	void *p;
+	int n;
+
+	assert(size);
+
+	p = alloc_pages_flags(order, AREA_DMA31 | flags);
+	if (!p || !test_facility(158))
+		return p;
+
+	n = share_pages(p, 1 << order);
+	if (n == 1 << order)
+		return p;
+
+	unshare_pages(p, n);
+	free_pages(p);
+	return NULL;
+}
+
+void free_io_mem(void *p, int size)
+{
+	int order = get_order(size >> PAGE_SHIFT);
+
+	assert(IS_ALIGNED((uintptr_t)p, PAGE_SIZE));
+
+	if (test_facility(158))
+		unshare_pages(p, 1 << order);
+	free_pages(p);
+}
diff --git a/lib/s390x/malloc_io.h b/lib/s390x/malloc_io.h
new file mode 100644
index 0000000..cc5fad7
--- /dev/null
+++ b/lib/s390x/malloc_io.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * I/O allocations
+ *
+ * Copyright (c) 2021 IBM Corp
+ *
+ * Authors:
+ *  Pierre Morel <pmorel@linux.ibm.com>
+ *
+ */
+#ifndef _S390X_MALLOC_IO_H_
+#define _S390X_MALLOC_IO_H_
+
+/*
+ * Allocates a page aligned page bound range of contiguous real or
+ * absolute memory in the DMA31 region large enough to contain size
+ * bytes.
+ * If Protected Virtualisation facility is present, shares the pages
+ * with the host.
+ * If all the pages for the specified size cannot be reserved,
+ * the function rewinds the partial allocation and a NULL pointer
+ * is returned.
+ *
+ * @size: the minimal size allocated in byte.
+ * @flags: the flags used for the underlying page allocator.
+ *
+ * Errors:
+ *   The allocation will assert the size parameter, will fail if the
+ *   underlying page allocator fail or in the case of protected
+ *   virtualisation if the sharing of the pages fails.
+ *
+ * Returns a pointer to the first page in case of success, NULL otherwise.
+ */
+void *alloc_io_mem(int size, int flags);
+
+/*
+ * Frees a previously memory space allocated by alloc_io_mem.
+ * If Protected Virtualisation facility is present, unshares the pages
+ * with the host.
+ * The address must be aligned on a page boundary otherwise an assertion
+ * breaks the program.
+ */
+void free_io_mem(void *p, int size);
+
+#endif /* _S390X_MALLOC_IO_H_ */
diff --git a/s390x/Makefile b/s390x/Makefile
index 08d85c9..f3b0fcc 100644
--- a/s390x/Makefile
+++ b/s390x/Makefile
@@ -64,6 +64,7 @@ cflatobjs += lib/s390x/smp.o
 cflatobjs += lib/s390x/vm.o
 cflatobjs += lib/s390x/css_dump.o
 cflatobjs += lib/s390x/css_lib.o
+cflatobjs += lib/s390x/malloc_io.o
 
 OBJDIRS += lib/s390x
 
-- 
2.17.1
