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

[Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>]

On 7/10/2017 11:58 PM, Brian Gerst wrote:
> On Mon, Jul 10, 2017 at 3:50 PM, Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org> wrote:
>> On 7/8/2017 7:57 AM, Brian Gerst wrote:
>>>
>>> On Fri, Jul 7, 2017 at 9:39 AM, Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
>>> wrote:
>>>>
>>>> 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-5C7GfCeVMHo@public.gmane.org>
>>>> ---
>>>>    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:
>>
>> http://marc.info/?l=linux-kernel&m=149803067811436&w=2
>>
>> Thanks,
>> Tom
> 
> 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.

Thanks,
Tom

> 
> --
> Brian Gerst
>