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

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

On 6/21/2017 2:37 AM, Thomas Gleixner wrote:
> 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.
Ok, that sounds good.  I'll remove the check and usage of phys_to_virt()
and update the changelog with additional detail about that.

Thanks,
Tom

> Thanks,
>
>         tglx
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