Re: [kvm-unit-tests PATCH v4 2/3] s390x: define UV compatible I/O allocation

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On 1/21/21 10:32 AM, Thomas Huth wrote:

...snip...

+#include <asm/facility.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))
+            return i;

Just a matter of taste, but you could replace the "return i" here also with a "break" since you're returning i below anyway.

right a single out point is always better.


+    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_pages(int size, int flags)

I still think the naming or size parameter is confusing here. If I read something like alloc_io_pages(), I'd expect a "num_pages" parameter. So if you want to keep the "size" in bytes, I'd suggest to rename the function to "alloc_io_mem" instead.

OK, I rename the function, allowing the user to keep a simple interface
without having to calculate the page order.


+{
+    int order = (size >> PAGE_SHIFT);

I think this is wrong. According to the description of alloc_pages_flag, it allocates "1ull << order" pages.
So you likely want to do this instead here:

         int order = get_order(size >> PAGE_SHIFT);

you are absolutely right.


+    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_pages(void *p, int size)
+{
+    int order = size >> PAGE_SHIFT;

dito?

yes :(


+    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..494dfe9
--- /dev/null
+++ b/lib/s390x/malloc_io.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0 */

GPL-2.0-only please.

almmost... I use:
/* SPDX-License-Identifier: GPL-2.0-or-later */

as in other files updated by janosch if this is not a problem.


+/*
+ * I/O allocations
+ *
+ * Copyright (c) 2021 IBM Corp
+ *
+ * Authors:
+ *  Pierre Morel <pmorel@xxxxxxxxxxxxx>
+ *
+ */
+#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 Virtualization 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.

I think "virtualization" (with an z) is more common than "virtualisation".

OK


Thanks,
Pierre

--
Pierre Morel
IBM Lab Boeblingen



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