Currently memremap(MEMREMAP_WB) produces decrypted/shared mapping:

memremap(MEMREMAP_WB)
  arch_memremap_wb()
    ioremap_cache()
      __ioremap_caller(.encrytped = false)

It is a bad default. On TDX guests, access via shared mapping can be
destructive[1].

Kernel already provides a way to request decrypted mapping explicitly
via MEMREMAP_DEC flag.

Make memremap(MEMREMAP_WB) produce encrypted/private mapping by default
unless MEMREMAP_DEC is specified.

It fixes crash on kexec in TDX guests if CONFIG_EISA is enabled.

[1] https://lore.kernel.org/all/20240822095122.736522-1-kirill.shutemov@linux.intel.com

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Ashish Kalra <ashish.kalra@amd.com>
Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>
---
 arch/x86/include/asm/io.h | 3 +++
 arch/x86/mm/ioremap.c     | 8 ++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 1d60427379c9..1a3a34b40598 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -180,6 +180,9 @@ extern void __iomem *ioremap_prot(resource_size_t offset, unsigned long size, un
 extern void __iomem *ioremap_encrypted(resource_size_t phys_addr, unsigned long size);
 #define ioremap_encrypted ioremap_encrypted
 
+void *arch_memremap_wb(phys_addr_t phys_addr, size_t size, unsigned long flags);
+#define arch_memremap_wb arch_memremap_wb
+
 /**
  * ioremap     -   map bus memory into CPU space
  * @offset:    bus address of the memory
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 70b02fc61d93..fc65a81fd777 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -503,6 +503,14 @@ void iounmap(volatile void __iomem *addr)
 }
 EXPORT_SYMBOL(iounmap);
 
+void *arch_memremap_wb(phys_addr_t phys_addr, size_t size, unsigned long flags)
+{
+	if (flags & MEMREMAP_DEC)
+		return ioremap_cache(phys_addr, size);
+
+	return ioremap_encrypted(phys_addr, size);
+}
+
 /*
  * Convert a physical pointer to a virtual kernel pointer for /dev/mem
  * access
-- 
2.45.2

Hi Kirill,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tip/master]
[also build test WARNING on tip/x86/mm linus/master tip/auto-latest tip/x86/core v6.12-rc3 next-20241018]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Kirill-A-Shutemov/memremap-Pass-down-MEMREMAP_-flags-to-arch_memremap_wb/20241018-001138
base:   tip/master
patch link:    https://lore.kernel.org/r/20241017155642.1942514-3-kirill.shutemov%40linux.intel.com
patch subject: [PATCH 2/2] x86/mm: Make memremap(MEMREMAP_WB) map memory as encrypted by default
config: i386-randconfig-061-20241019 (https://download.01.org/0day-ci/archive/20241020/202410200112.Ut6HtXKD-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241020/202410200112.Ut6HtXKD-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202410200112.Ut6HtXKD-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> arch/x86/mm/ioremap.c:509:37: sparse: sparse: incorrect type in return expression (different address spaces) @@     expected void * @@     got void [noderef] __iomem * @@
   arch/x86/mm/ioremap.c:509:37: sparse:     expected void *
   arch/x86/mm/ioremap.c:509:37: sparse:     got void [noderef] __iomem *
   arch/x86/mm/ioremap.c:511:33: sparse: sparse: incorrect type in return expression (different address spaces) @@     expected void * @@     got void [noderef] __iomem * @@
   arch/x86/mm/ioremap.c:511:33: sparse:     expected void *
   arch/x86/mm/ioremap.c:511:33: sparse:     got void [noderef] __iomem *

vim +509 arch/x86/mm/ioremap.c

   505	
   506	void *arch_memremap_wb(phys_addr_t phys_addr, size_t size, unsigned long flags)
   507	{
   508		if (flags & MEMREMAP_DEC)
 > 509			return ioremap_cache(phys_addr, size);
   510	
   511		return ioremap_encrypted(phys_addr, size);
   512	}
   513	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki