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

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Message-ID: <5d7f9a32-89d1-e2f2-4dea-98527ac3492e@amd.com>
Date:   Thu, 27 Jul 2017 09:57:45 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Young <dyoung@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v1 2/2] acpi, x86: Remove encryption mask from ACPI page
 protection type

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@....com>
>> ---
>>   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

>