linux-kernel - [RFC PATCH v2 08/32] x86: Use PAGE_KERNEL protection for ioremap of memory page

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Date:   Thu, 2 Mar 2017 10:13:32 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     <simon.guinot@...uanux.org>, <linux-efi@...r.kernel.org>,
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Subject: [RFC PATCH v2 08/32] x86: Use PAGE_KERNEL protection for ioremap of
 memory page

From: Tom Lendacky <thomas.lendacky@....com>

In order for memory pages to be properly mapped when SEV is active, we
need to use the PAGE_KERNEL protection attribute as the base protection.
This will insure that memory mapping of, e.g. ACPI tables, receives the
proper mapping attributes.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/mm/ioremap.c |    8 ++++++++
 include/linux/mm.h    |    1 +
 kernel/resource.c     |   40 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index c400ab5..481c999 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -151,7 +151,15 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
 		pcm = new_pcm;
 	}
 
+	/*
+	 * If the page being mapped is in memory and SEV is active then
+	 * make sure the memory encryption attribute is enabled in the
+	 * resulting mapping.
+	 */
 	prot = PAGE_KERNEL_IO;
+	if (sev_active() && page_is_mem(pfn))
+		prot = __pgprot(pgprot_val(prot) | _PAGE_ENC);
+
 	switch (pcm) {
 	case _PAGE_CACHE_MODE_UC:
 	default:
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b84615b..825df27 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -445,6 +445,7 @@ static inline int get_page_unless_zero(struct page *page)
 }
 
 extern int page_is_ram(unsigned long pfn);
+extern int page_is_mem(unsigned long pfn);
 
 enum {
 	REGION_INTERSECTS,
diff --git a/kernel/resource.c b/kernel/resource.c
index 9b5f044..db56ba3 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -518,6 +518,46 @@ int __weak page_is_ram(unsigned long pfn)
 }
 EXPORT_SYMBOL_GPL(page_is_ram);
 
+/*
+ * This function returns true if the target memory is marked as
+ * IORESOURCE_MEM and IORESOUCE_BUSY and described as other than
+ * IORES_DESC_NONE (e.g. IORES_DESC_ACPI_TABLES).
+ */
+static int walk_mem_range(unsigned long start_pfn, unsigned long nr_pages)
+{
+	struct resource res;
+	unsigned long pfn, end_pfn;
+	u64 orig_end;
+	int ret = -1;
+
+	res.start = (u64) start_pfn << PAGE_SHIFT;
+	res.end = ((u64)(start_pfn + nr_pages) << PAGE_SHIFT) - 1;
+	res.flags = IORESOURCE_MEM | IORESOURCE_BUSY;
+	orig_end = res.end;
+	while ((res.start < res.end) &&
+		(find_next_iomem_res(&res, IORES_DESC_NONE, true) >= 0)) {
+		pfn = (res.start + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		end_pfn = (res.end + 1) >> PAGE_SHIFT;
+		if (end_pfn > pfn)
+			ret = (res.desc != IORES_DESC_NONE) ? 1 : 0;
+		if (ret)
+			break;
+		res.start = res.end + 1;
+		res.end = orig_end;
+	}
+	return ret;
+}
+
+/*
+ * This generic page_is_mem() returns true if specified address is
+ * registered as memory in iomem_resource list.
+ */
+int __weak page_is_mem(unsigned long pfn)
+{
+	return walk_mem_range(pfn, 1) == 1;
+}
+EXPORT_SYMBOL_GPL(page_is_mem);
+
 /**
  * region_intersects() - determine intersection of region with known resources
  * @start: region start address