x86: Make ARCH_USE_MEMREMAP_PROT a generic Kconfig symbol

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 <[e-mail]>
Cc: AKASHI Takahiro <[e-mail]>
Cc: Alexander Graf <[e-mail]>
Cc: Bjorn Andersson <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Heinrich Schuchardt <[e-mail]>
Cc: Jeffrey Hugo <[e-mail]>
Cc: Lee Jones <[e-mail]>
Cc: Leif Lindholm <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Matt Fleming <[e-mail]>
Cc: Peter Jones <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Sai Praneeth Prakhya <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/Kconfig

···
 	  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"

arch/x86/Kconfig

···
 	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
···
 
 	  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

arch/x86/mm/ioremap.c

···
 	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)
···
 
 	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;