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From: Stephen Boyd <swboyd@chromium.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
	Evan Green <evgreen@chromium.org>,
	Rob Herring <robh+dt@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Andy Gross <agross@kernel.org>, Will Deacon <will.deacon@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>
Subject: [PATCH v2 3/5] memremap: Add support for read-only memory mappings
Date: Fri, 14 Jun 2019 13:37:15 -0700	[thread overview]
Message-ID: <20190614203717.75479-4-swboyd@chromium.org> (raw)
In-Reply-To: <20190614203717.75479-1-swboyd@chromium.org>

Sometimes we have memories that are supposed to be read-only, but when
we map these regions the best we can do is map them as write-back with
MEMREMAP_WB. Introduce a read-only memory mapping (MEMREMAP_RO) that
allows us to map reserved memory regions as read-only. This way, we're
less likely to see these special memory regions become corrupted by
stray writes to them.

Cc: Evan Green <evgreen@chromium.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Andy Gross <agross@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
 include/linux/io.h |  1 +
 kernel/iomem.c     | 15 +++++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/linux/io.h b/include/linux/io.h
index 32e30e8fb9db..16c7f4498869 100644
--- a/include/linux/io.h
+++ b/include/linux/io.h
@@ -159,6 +159,7 @@ enum {
 	MEMREMAP_WC = 1 << 2,
 	MEMREMAP_ENC = 1 << 3,
 	MEMREMAP_DEC = 1 << 4,
+	MEMREMAP_RO = 1 << 5,
 };
 
 void *memremap(resource_size_t offset, size_t size, unsigned long flags);
diff --git a/kernel/iomem.c b/kernel/iomem.c
index 93c264444510..10d5ef0ff09e 100644
--- a/kernel/iomem.c
+++ b/kernel/iomem.c
@@ -19,6 +19,13 @@ static void *arch_memremap_wb(resource_size_t offset, unsigned long size)
 }
 #endif
 
+#ifndef arch_memremap_ro
+static void *arch_memremap_ro(resource_size_t offset, unsigned long size)
+{
+	return NULL;
+}
+#endif
+
 #ifndef arch_memremap_can_ram_remap
 static bool arch_memremap_can_ram_remap(resource_size_t offset, size_t size,
 					unsigned long flags)
@@ -84,7 +91,10 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)
 	}
 
 	/* Try all mapping types requested until one returns non-NULL */
-	if (flags & MEMREMAP_WB) {
+	if ((flags & MEMREMAP_RO) && is_ram != REGION_INTERSECTS)
+		addr = arch_memremap_ro(offset, size);
+
+	if (!addr && (flags & MEMREMAP_WB)) {
 		/*
 		 * MEMREMAP_WB is special in that it can be satisfied
 		 * from the direct map.  Some archs depend on the
@@ -103,7 +113,8 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)
 	 * address mapping.  Enforce that this mapping is not aliasing
 	 * System RAM.
 	 */
-	if (!addr && is_ram == REGION_INTERSECTS && flags != MEMREMAP_WB) {
+	if (!addr && is_ram == REGION_INTERSECTS &&
+	    (flags != MEMREMAP_WB || flags != MEMREMAP_RO)) {
 		WARN_ONCE(1, "memremap attempted on ram %pa size: %#lx\n",
 				&offset, (unsigned long) size);
 		return NULL;
-- 
Sent by a computer through tubes


  parent reply	other threads:[~2019-06-14 20:37 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-14 20:37 [PATCH v2 0/5] Read-only memremap() Stephen Boyd
2019-06-14 20:37 ` [PATCH v2 1/5] reserved_mem: Add a devm_memremap_reserved_mem() API Stephen Boyd
2019-06-14 20:37 ` [PATCH v2 2/5] soc: qcom: cmd-db: Migrate to devm_memremap_reserved_mem() Stephen Boyd
2019-06-14 20:37 ` Stephen Boyd [this message]
2019-07-10 14:14   ` [PATCH v2 3/5] memremap: Add support for read-only memory mappings Will Deacon
2019-07-18 18:00     ` Stephen Boyd
2019-06-14 20:37 ` [PATCH v2 4/5] arm64: Add support for arch_memremap_ro() Stephen Boyd
2019-06-14 20:37 ` [PATCH v2 5/5] soc: qcom: cmd-db: Map with read-only mappings Stephen Boyd

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