Re: [PATCH v1 2/2] acpi, x86: Remove encryption mask from ACPI page protection type

[Tom Lendacky]

On 7/27/2017 9:41 AM, Borislav Petkov wrote:
> On Wed, Jul 26, 2017 at 01:04:34PM -0500, Tom Lendacky wrote:
> > The function arch_apei_get_mem_attributes() is used to set the page
> > protection type for ACPI physical addresses. When SME is active, the
> > associated protection type needs to not have the encryption mask set
> > since the ACPI tables live in un-encrypted memory. Modify the
> > arch_apei_get_mem_attributes() function to remove the encryption mask
> > when SME is active by returning the PAGE_KERNEL_IO protection type.
> >
> > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > ---
> >   arch/x86/include/asm/acpi.h | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
> > index 562286f..89df39d 100644
> > --- a/arch/x86/include/asm/acpi.h
> > +++ b/arch/x86/include/asm/acpi.h
> > @@ -34,6 +34,7 @@
> >   
> >   #ifdef CONFIG_ACPI_APEI
> >   # include <asm/pgtable_types.h>
> > +# include <linux/mem_encrypt.h>
> >   #endif
> >   
> >   #ifdef CONFIG_ACPI
> > @@ -164,8 +165,12 @@ static inline pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
> >   	 * anything other than PAGE_KERNEL (some arm64 platforms
> >   	 * require the equivalent of PAGE_KERNEL_NOCACHE), return that
> >   	 * until we know differently.
> > +	 *
> > +	 * When SME is active, the ACPI information will not reside in
> > +	 * in memory in an encrypted state so return a protection attribute
> > +	 * that does not have the encryption bit set.
> >   	 */
> > -	 return PAGE_KERNEL;
> > +	 return sme_active() ? PAGE_KERNEL_IO : PAGE_KERNEL;
>
> Why isn't there a PAGE_KERNEL_NOENC define which you can simply return
> instead of testing?

Sounds like something I should add to pgtable_types.h (which has a
#define for PAGE_KERNEL_EXEC_NOENC, but not PAGE_KERNEL_NOENC). I'll
create that #define.

As for the sme_active() check I was getting ahead of myself since
under SEV the encryption mask is needed.  I'll change it to just
return PAGE_KERNEL_NOENC and then worry about the SEV change in
the SEV patches.

Thanks,
Tom

>