linux-kernel - Re: [PATCH v5 26/32] x86, drm, fbdev: Do not specify encrypted memory for video mappings

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Date:   Tue, 30 May 2017 15:07:05 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kasan-dev@...glegroups.com>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 26/32] x86, drm, fbdev: Do not specify encrypted memory
 for video mappings

On 5/16/2017 12:35 PM, Borislav Petkov wrote:
> On Tue, Apr 18, 2017 at 04:20:56PM -0500, Tom Lendacky wrote:
>> Since video memory needs to be accessed decrypted, be sure that the
>> memory encryption mask is not set for the video ranges.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>> ---
>>   arch/x86/include/asm/vga.h       |   13 +++++++++++++
>>   arch/x86/mm/pageattr.c           |    2 ++
>>   drivers/gpu/drm/drm_gem.c        |    2 ++
>>   drivers/gpu/drm/drm_vm.c         |    4 ++++
>>   drivers/gpu/drm/ttm/ttm_bo_vm.c  |    7 +++++--
>>   drivers/gpu/drm/udl/udl_fb.c     |    4 ++++
>>   drivers/video/fbdev/core/fbmem.c |   12 ++++++++++++
>>   7 files changed, 42 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/vga.h b/arch/x86/include/asm/vga.h
>> index c4b9dc2..5c7567a 100644
>> --- a/arch/x86/include/asm/vga.h
>> +++ b/arch/x86/include/asm/vga.h
>> @@ -7,12 +7,25 @@
>>   #ifndef _ASM_X86_VGA_H
>>   #define _ASM_X86_VGA_H
>>   
>> +#include <asm/cacheflush.h>
>> +
>>   /*
>>    *	On the PC, we can just recalculate addresses and then
>>    *	access the videoram directly without any black magic.
>> + *	To support memory encryption however, we need to access
>> + *	the videoram as decrypted memory.
>>    */
>>   
>> +#ifdef CONFIG_AMD_MEM_ENCRYPT
>> +#define VGA_MAP_MEM(x, s)					\
>> +({								\
>> +	unsigned long start = (unsigned long)phys_to_virt(x);	\
>> +	set_memory_decrypted(start, (s) >> PAGE_SHIFT);		\
>> +	start;							\
>> +})
>> +#else
>>   #define VGA_MAP_MEM(x, s) (unsigned long)phys_to_virt(x)
>> +#endif
> 
> Can we push the check in and save us the ifdeffery?
> 
> #define VGA_MAP_MEM(x, s)                                       \
> ({                                                              \
>          unsigned long start = (unsigned long)phys_to_virt(x);   \
>                                                                  \
>          if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))                 \
>                  set_memory_decrypted(start, (s) >> PAGE_SHIFT); \
>                                                                  \
>          start;                                                  \
> })
> 
> It does build here. :)
> 

That works for me and it's a lot cleaner.  I'll make the change.

Thanks,
Tom