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Re: [Xen-devel] [PATCH v9 07/38] x86/mm: Remove phys_to_virt() usage in ioremap()

On 7/10/2017 11:58 PM, Brian Gerst wrote:
On Mon, Jul 10, 2017 at 3:50 PM, Tom Lendacky <thomas.lendacky@xxxxxxx> wrote:
On 7/8/2017 7:57 AM, Brian Gerst wrote:

On Fri, Jul 7, 2017 at 9:39 AM, Tom Lendacky <thomas.lendacky@xxxxxxx>

Currently there is a check if the address being mapped is in the ISA
range (is_ISA_range()), and if it is, then phys_to_virt() is used to
perform the mapping. When SME is active, the default is to add pagetable
mappings with the encryption bit set unless specifically overridden. The
resulting pagetable mapping from phys_to_virt() will result in a mapping
that has the encryption bit set. With SME, the use of ioremap() is
intended to generate pagetable mappings that do not have the encryption
bit set through the use of the PAGE_KERNEL_IO protection value.

Rather than special case the SME scenario, remove the ISA range check and
usage of phys_to_virt() and have ISA range mappings continue through the
remaining ioremap() path.

Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
   arch/x86/mm/ioremap.c |    7 +------
   1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 4c1b5fd..bfc3e2d 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -13,6 +13,7 @@
   #include <linux/slab.h>
   #include <linux/vmalloc.h>
   #include <linux/mmiotrace.h>
+#include <linux/mem_encrypt.h>

   #include <asm/set_memory.h>
   #include <asm/e820/api.h>
@@ -106,12 +107,6 @@ static void __iomem
*__ioremap_caller(resource_size_t phys_addr,

-        * Don't remap the low PCI/ISA area, it's always mapped..
-        */
-       if (is_ISA_range(phys_addr, last_addr))
-               return (__force void __iomem *)phys_to_virt(phys_addr);
-       /*
           * Don't allow anybody to remap normal RAM that we're using..
          pfn      = phys_addr >> PAGE_SHIFT;

Removing this also affects 32-bit, which is more likely to access
legacy devices in this range.  Put in a check for SME instead

I originally had a check for SME here in a previous version of the
patch.  Thomas Gleixner recommended removing the check so that the code
path was always exercised regardless of the state of SME in order to
better detect issues:



Looking a bit closer, this shortcut doesn't set the caching
attributes.  So it's probably best to get rid of it anyways.  Also
note, there is a corresponding check in iounmap().

Good catch.  I'll update the patch to include the removal of the ISA
checks in the iounmap() path as well.


Brian Gerst

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