Re: [Xen-devel] [PATCH v7 07/36] x86/mm: Don't use phys_to_virt in ioremap() if SME is active

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

On Fri, 16 Jun 2017, Tom Lendacky 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, however, this will result
> in the mapping having the encryption bit set when it is expected that
> an ioremap() should not have the encryption bit set. So only use the
> phys_to_virt() function if SME is not active
> 
> Reviewed-by: Borislav Petkov <bp@xxxxxxx>
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  arch/x86/mm/ioremap.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index 4c1b5fd..a382ba9 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>
> @@ -106,9 +107,11 @@ static void __iomem *__ioremap_caller(resource_size_t 
> phys_addr,
>       }
>  
>       /*
> -      * Don't remap the low PCI/ISA area, it's always mapped..
> +      * Don't remap the low PCI/ISA area, it's always mapped.
> +      *   But if SME is active, skip this so that the encryption bit
> +      *   doesn't get set.
>        */
> -     if (is_ISA_range(phys_addr, last_addr))
> +     if (is_ISA_range(phys_addr, last_addr) && !sme_active())
>               return (__force void __iomem *)phys_to_virt(phys_addr);

More thoughts about that.

Making this conditional on !sme_active() is not the best idea. I'd rather
remove that whole thing and make it unconditional so the code pathes get
always exercised and any subtle wreckage is detected on a broader base and
not only on that hard to access and debug SME capable machine owned by Joe
User.

Thanks,

        tglx

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