Re: [PATCH] x86/HVM: fix hvmemul_rep_outs_set_context()

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 23/11/17 15:09, Jan Beulich wrote:
> There were two issues with this function: Its use of
> hvmemul_do_pio_buffer() was wrong (the function deals only with
> individual port accesses, not repeated ones, i.e. passing it
> "*reps * bytes_per_rep" does not have the intended effect). And it
> could have processed a larger set of operations in one go than was
> probably intended (limited just by the size that xmalloc() can hand
> back).
>
> By converting to proper use of hvmemul_do_pio_buffer(), no intermediate
> buffer is needed at all. As a result a preemption check is being added.
>
> Also drop unused parameters from the function.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

While this does look like real bug, and bugfix, it isn't the issue I'm
hitting.  I've distilled the repro scenario down to a tiny XTF test,
which is just a `rep outsb` with a buffer which crosses a page boundary.

The results are reliably:

(d1) --- Xen Test Framework ---
(d1) Environment: HVM 32bit (No paging)
(d1) Test hvm-print
(d1) String crossing a page boundary
(XEN) MMIO emulation failed (1): d1v0 32bit @ 0010:001032b0 -> 5e c3 8d
b4 26 00 00 00 00 8d bc 27 00 00 00 00
(d1) Test result: SUCCESS

The Port IO hits a retry because of hitting the page boundary, and the
retry logic successes, as evident by all data hitting hvm_print_line(). 
Somewhere however, the PIO turns into MMIO, and a failure is reported
after the PIO completed successfully.  %rip in the failure message
points after the `rep outsb`, rather than at it.

If anyone has any ideas, I'm all ears.  If not, I will try to find some
time to look deeper into the issue.

~Andrew

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>From 9141a36374f52434a291e3be41bd259cfb9bda72 Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Thu, 23 Nov 2017 18:31:40 +0000
Subject: [PATCH] MMIO failure trigger

---
 tests/hvm-print/Makefile |  9 +++++++++
 tests/hvm-print/main.c   | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)
 create mode 100644 tests/hvm-print/Makefile
 create mode 100644 tests/hvm-print/main.c

diff --git a/tests/hvm-print/Makefile b/tests/hvm-print/Makefile
new file mode 100644
index 0000000..c70bede
--- /dev/null
+++ b/tests/hvm-print/Makefile
@@ -0,0 +1,9 @@
+include $(ROOT)/build/common.mk
+
+NAME      := hvm-print
+CATEGORY  := utility
+TEST-ENVS := hvm32
+
+obj-perenv += main.o
+
+include $(ROOT)/build/gen.mk
diff --git a/tests/hvm-print/main.c b/tests/hvm-print/main.c
new file mode 100644
index 0000000..882b716
--- /dev/null
+++ b/tests/hvm-print/main.c
@@ -0,0 +1,40 @@
+/**
+ * @file tests/hvm-print/main.c
+ * @ref test-hvm-print
+ *
+ * @page test-hvm-print hvm-print
+ *
+ * @todo Docs for test-hvm-print
+ *
+ * @see tests/hvm-print/main.c
+ */
+#include <xtf.h>
+
+const char test_title[] = "Test hvm-print";
+
+static char buf[2 * PAGE_SIZE] __page_aligned_bss;
+
+void test_main(void)
+{
+    char *ptr = &buf[4090];
+    size_t len;
+
+    strcpy(ptr, "String crossing a page boundary\n");
+    len = strlen(ptr);
+
+    asm volatile("rep; outsb"
+                 : "+S" (ptr), "+c" (len)
+                 : "d" (0xe9));
+
+    xtf_success(NULL);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
-- 
2.1.4


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