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Re: [Minios-devel] [UNIKRAFT PATCHv6 07/37] plat/common: Add cache maintenance support for arm64



Hi Wei,

On 09/14/2018 08:56 AM, Wei Chen wrote:
When MMU is disabled, when we modify some data, for example, write
page-table, we will write with Device nGnRnE attributes. So the
cache will be bypassed. But the cache may still contain stall data
that we will hit when enabling MMU and cache. To prevent such issue,
we need to clean the cache potentially before and after updating
the page-table area.

So we introduce the cache maintenance functions in this patch.

Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
---
  plat/common/arm/cache64.S                | 85 ++++++++++++++++++++++++
  plat/common/include/arm/arm64/cpu_defs.h | 46 +++++++++++++
  plat/common/include/arm/cpu_defs.h       | 44 ++++++++++++
  plat/kvm/Makefile.uk                     |  1 +
  4 files changed, 176 insertions(+)
  create mode 100644 plat/common/arm/cache64.S
  create mode 100644 plat/common/include/arm/arm64/cpu_defs.h
  create mode 100644 plat/common/include/arm/cpu_defs.h

diff --git a/plat/common/arm/cache64.S b/plat/common/arm/cache64.S
new file mode 100644
index 0000000..a725557
--- /dev/null
+++ b/plat/common/arm/cache64.S
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+/*
+ * Authors: Wei Chen <wei.chen@xxxxxxx>
+ *
+ * Copyright (c) 2014 Robin Randhawa
+ * Copyright (c) 2015 The FreeBSD Foundation
+ * All rights reserved.
+ * Copyright (c) 2018, Arm Ltd. All rights reserved.

From the copyright, I suspect the code is from FreeBSD. However, I can't find anything close to it in the source. Did I miss anything?

In general, it is a good idea to mention where you code comes from and the commit used in the commit message. This helps to check whether code has been updated afterwards.

+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ * THIS HEADER MAY NOT BE EXTRACTED OR MODIFIED IN ANY WAY.
+ */
+#include <uk/asm.h>
+#include <arm/cpu_defs.h>
+
+/*
+ * Function to invalidate I/D cache. This takes the start address in x0,
+ * length in x1. It will corrupt x0 ~ x5.
+ */
+ENTRY(invalidate_idcache_range)

IHMO, the name is misleading. You don't only invalidate the cache, you clean it as well.

But I am a bit confused of the purpose of the function in the context you are using it. Why do you need to invalidate the I-Cache? The boot code will not rewrite itself, so the I-Cache will not need an invalidation.

+       /* Get information about the caches from CTR_EL0 */
+       mrs     x3, ctr_el0
+       mov     x2, #CTR_BYTES_PER_WORD
+
+       /* Get minimum D cache line size */
+       ubfx    x4, x3, #CTR_DMINLINE_SHIFT, #CTR_DMINLINE_WIDTH
+       lsl     x4, x2, x4
+
+       /* Get minimum I cache line size */
+       and     x5, x3, #CTR_IMINLINE_MASK
+       lsl     x5, x2, x5
+
+       /* Select the smaller one as I/D cache line size */
+       cmp     x5, x4
+       csel    x3, x5, x4, le
+
+       /* Align the start address to line size */
+       sub     x4, x3, #1
+       and     x2, x0, x4
+       add     x1, x1, x2
+       bic     x0, x0, x4
+1:
+       /* clean and invalidate D cache by I/D cache line size */
+       dc      civac, x0
+       dsb     ish

This looks incorrect given you use it before the MMU is on. I think you want to use nsh here (if not sy).

+
+       /* clean and invalidate I cache by I/D cache line size */
+       ic      ivau, x0
+       dsb     ish

Ditto.

+
+       /* Move to next line and reduce the size */
+       add     x0, x0, x3
+       subs    x1, x1, x3
+
+       /* Check if all range has been invalidated */
+       b.hi    1b
+
+       isb
+
+       ret
+END(invalidate_idcache_range)

Cheers,

--
Julien Grall

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