[PATCH v5 15/16] x86/tdx: Implement ioremap_host_shared for x86

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

From: Andi Kleen <ak@linux.intel.com>

Implement ioremap_host_shared for x86. In TDX most memory is encrypted,
but some memory that is used to communicate with the host must
be declared shared with special page table attributes and a
special hypercall. Previously all ioremaped memory was declared
shared, but this leads to various BIOS tables and other private
state being shared, which is a security risk.

This patch replaces the unconditional ioremap sharing with an explicit
ioremap_host_shared that enables sharing.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---

Changes since v4:
 * Rebased on top of Tom Lendacky's CC guest
   changes (https://www.spinics.net/lists/linux-tip-commits/msg58716.html)

 arch/x86/include/asm/io.h |  4 ++++
 arch/x86/mm/ioremap.c     | 41 ++++++++++++++++++++++++++++++---------
 2 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 67e0c4a0a0f4..521b239c013f 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -380,6 +380,10 @@ extern void __iomem *ioremap_wc(resource_size_t offset, unsigned long size);
 extern void __iomem *ioremap_wt(resource_size_t offset, unsigned long size);
 #define ioremap_wt ioremap_wt
 
+extern void __iomem *ioremap_host_shared(resource_size_t offset,
+					 unsigned long size);
+#define ioremap_host_shared ioremap_host_shared
+
 extern bool is_early_ioremap_ptep(pte_t *ptep);
 
 #define IO_SPACE_LIMIT 0xffff
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 83daa3f8f39c..a83a69045f61 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -178,7 +178,8 @@ static void __ioremap_check_mem(resource_size_t addr, unsigned long size,
  */
 static void __iomem *
 __ioremap_caller(resource_size_t phys_addr, unsigned long size,
-		 enum page_cache_mode pcm, void *caller, bool encrypted)
+		 enum page_cache_mode pcm, void *caller, bool encrypted,
+		 bool shared)
 {
 	unsigned long offset, vaddr;
 	resource_size_t last_addr;
@@ -248,7 +249,7 @@ __ioremap_caller(resource_size_t phys_addr, unsigned long size,
 	prot = PAGE_KERNEL_IO;
 	if ((io_desc.flags & IORES_MAP_ENCRYPTED) || encrypted)
 		prot = pgprot_encrypted(prot);
-	else if (cc_platform_has(CC_ATTR_GUEST_SHARED_MAPPING_INIT))
+	else if (shared)
 		prot = pgprot_cc_guest(prot);
 
 	switch (pcm) {
@@ -340,7 +341,8 @@ void __iomem *ioremap(resource_size_t phys_addr, unsigned long size)
 	enum page_cache_mode pcm = _PAGE_CACHE_MODE_UC_MINUS;
 
 	return __ioremap_caller(phys_addr, size, pcm,
-				__builtin_return_address(0), false);
+				__builtin_return_address(0), false,
+				false);
 }
 EXPORT_SYMBOL(ioremap);
 
@@ -373,7 +375,8 @@ void __iomem *ioremap_uc(resource_size_t phys_addr, unsigned long size)
 	enum page_cache_mode pcm = _PAGE_CACHE_MODE_UC;
 
 	return __ioremap_caller(phys_addr, size, pcm,
-				__builtin_return_address(0), false);
+				__builtin_return_address(0), false,
+				false);
 }
 EXPORT_SYMBOL_GPL(ioremap_uc);
 
@@ -390,10 +393,29 @@ EXPORT_SYMBOL_GPL(ioremap_uc);
 void __iomem *ioremap_wc(resource_size_t phys_addr, unsigned long size)
 {
 	return __ioremap_caller(phys_addr, size, _PAGE_CACHE_MODE_WC,
-					__builtin_return_address(0), false);
+					__builtin_return_address(0), false,
+					false);
 }
 EXPORT_SYMBOL(ioremap_wc);
 
+/**
+ * ioremap_host_shared - map memory into CPU space shared with host
+ * @phys_addr:	bus address of the memory
+ * @size:	size of the resource to map
+ *
+ * This version of ioremap ensures that the memory is marked shared
+ * with the host. This is useful for confidential guests.
+ *
+ * Must be freed with iounmap.
+ */
+void __iomem *ioremap_host_shared(resource_size_t phys_addr, unsigned long size)
+{
+	return __ioremap_caller(phys_addr, size, _PAGE_CACHE_MODE_UC,
+			__builtin_return_address(0), false,
+			cc_platform_has(CC_ATTR_GUEST_SHARED_MAPPING_INIT));
+}
+EXPORT_SYMBOL(ioremap_host_shared);
+
 /**
  * ioremap_wt	-	map memory into CPU space write through
  * @phys_addr:	bus address of the memory
@@ -407,21 +429,22 @@ EXPORT_SYMBOL(ioremap_wc);
 void __iomem *ioremap_wt(resource_size_t phys_addr, unsigned long size)
 {
 	return __ioremap_caller(phys_addr, size, _PAGE_CACHE_MODE_WT,
-					__builtin_return_address(0), false);
+					__builtin_return_address(0), false,
+					false);
 }
 EXPORT_SYMBOL(ioremap_wt);
 
 void __iomem *ioremap_encrypted(resource_size_t phys_addr, unsigned long size)
 {
 	return __ioremap_caller(phys_addr, size, _PAGE_CACHE_MODE_WB,
-				__builtin_return_address(0), true);
+				__builtin_return_address(0), true, false);
 }
 EXPORT_SYMBOL(ioremap_encrypted);
 
 void __iomem *ioremap_cache(resource_size_t phys_addr, unsigned long size)
 {
 	return __ioremap_caller(phys_addr, size, _PAGE_CACHE_MODE_WB,
-				__builtin_return_address(0), false);
+				__builtin_return_address(0), false, false);
 }
 EXPORT_SYMBOL(ioremap_cache);
 
@@ -430,7 +453,7 @@ void __iomem *ioremap_prot(resource_size_t phys_addr, unsigned long size,
 {
 	return __ioremap_caller(phys_addr, size,
 				pgprot2cachemode(__pgprot(prot_val)),
-				__builtin_return_address(0), false);
+				__builtin_return_address(0), false, false);
 }
 EXPORT_SYMBOL(ioremap_prot);
 
-- 
2.25.1