[PATCH 08/10] x86: make ARCH_USE_MEMREMAP_PROT a generic Kconfig symbol

[Ard Biesheuvel]

Turn ARCH_USE_MEMREMAP_PROT into a generic Kconfig symbol, and fix the
dependency expression to reflect that AMD_MEM_ENCRYPT depends on it,
instead of the other way around. This will permit ARCH_USE_MEMREMAP_PROT
to be selected by other architectures.

Note that the encryption related early memremap routines in
arch/x86/mm/ioremap.c cannot be built for 32-bit x86 without triggering
the following warning:

     arch/x86//mm/ioremap.c: In function 'early_memremap_encrypted':
  >> arch/x86/include/asm/pgtable_types.h:193:27: warning: conversion from
                     'long long unsigned int' to 'long unsigned int' changes
                     value from '9223372036854776163' to '355' [-Woverflow]
      #define __PAGE_KERNEL_ENC (__PAGE_KERNEL | _PAGE_ENC)
                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
     arch/x86//mm/ioremap.c:713:46: note: in expansion of macro '__PAGE_KERNEL_ENC'
       return early_memremap_prot(phys_addr, size, __PAGE_KERNEL_ENC);

which essentially means they are 64-bit only anyway. However, we cannot
make them dependent on CONFIG_ARCH_HAS_MEM_ENCRYPT, since that is always
defined, even for i386 (and changing that results in a slew of build errors)

So instead, build those routines only if CONFIG_AMD_MEM_ENCRYPT is
defined.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
 arch/Kconfig          | 3 +++
 arch/x86/Kconfig      | 5 +----
 arch/x86/mm/ioremap.c | 4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 4cfb6de48f79..9f0213213da8 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -885,6 +885,9 @@ config HAVE_ARCH_PREL32_RELOCATIONS
 	  architectures, and don't require runtime relocation on relocatable
 	  kernels.
 
+config ARCH_USE_MEMREMAP_PROT
+	bool
+
 source "kernel/gcov/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 15af091611e2..09c2c5600579 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1510,6 +1510,7 @@ config AMD_MEM_ENCRYPT
 	bool "AMD Secure Memory Encryption (SME) support"
 	depends on X86_64 && CPU_SUP_AMD
 	select DYNAMIC_PHYSICAL_MASK
+	select ARCH_USE_MEMREMAP_PROT
 	---help---
 	  Say yes to enable support for the encryption of system memory.
 	  This requires an AMD processor that supports Secure Memory
@@ -1529,10 +1530,6 @@ config AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT
 	  If set to N, then the encryption of system memory can be
 	  activated with the mem_encrypt=on command line option.
 
-config ARCH_USE_MEMREMAP_PROT
-	def_bool y
-	depends on AMD_MEM_ENCRYPT
-
 # Common NUMA Features
 config NUMA
 	bool "Numa Memory Allocation and Scheduler Support"
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 5378d10f1d31..0029604af8a4 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -705,7 +705,7 @@ bool phys_mem_access_encrypted(unsigned long phys_addr, unsigned long size)
 	return arch_memremap_can_ram_remap(phys_addr, size, 0);
 }
 
-#ifdef CONFIG_ARCH_USE_MEMREMAP_PROT
+#ifdef CONFIG_AMD_MEM_ENCRYPT
 /* Remap memory with encryption */
 void __init *early_memremap_encrypted(resource_size_t phys_addr,
 				      unsigned long size)
@@ -747,7 +747,7 @@ void __init *early_memremap_decrypted_wp(resource_size_t phys_addr,
 
 	return early_memremap_prot(phys_addr, size, __PAGE_KERNEL_NOENC_WP);
 }
-#endif	/* CONFIG_ARCH_USE_MEMREMAP_PROT */
+#endif	/* CONFIG_AMD_MEM_ENCRYPT */
 
 static pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)] __page_aligned_bss;
 
-- 
2.17.1