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

[Brian Gerst <brgerst@xxxxxxxxx>]

On Fri, Jul 7, 2017 at 9:39 AM, Tom Lendacky <thomas.lendacky@xxxxxxx> 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@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
(provided you follow my recommendations to not set the SME feature bit
on 32-bit even when the processor supports it).

--
Brian Gerst

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