linux-kernel - Re: [PATCH 3/3] X86, mpx: Intel MPX xstate feature definition

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Date:	Fri, 06 Dec 2013 09:23:22 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>, Qiaowei Ren <qiaowei.ren@...el.com>
CC:	Paolo Bonzini <pbonzini@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org, qemu-devel@...gnu.org,
	kvm@...r.kernel.org, Xudong Hao <xudong.hao@...el.com>,
	Liu Jinsong <jinsong.liu@...el.com>
Subject: Re: [PATCH 3/3] X86, mpx: Intel MPX xstate feature definition

On 12/06/2013 05:46 AM, Borislav Petkov wrote:
> 
> I'm guessing this and the struct lwp_struct above is being added so that
> you can have the LWP XSAVE area size? If so, you don't need it: LWP
> XSAVE area is 128 bytes at offset 832 according to my manuals so I'd
> guess having a u8 lwp_area[128] should be fine.
> 

Sure, but any reason to *not* document the internal structure?

> 
>> +	struct bndregs_struct bndregs;
>> +	struct bndcsr_struct bndcsr;
>>  	/* new processor state extensions will go here */
>>  } __attribute__ ((packed, aligned (64)));
>>  
>> diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
>> index 0415cda..5cd9de3 100644
>> --- a/arch/x86/include/asm/xsave.h
>> +++ b/arch/x86/include/asm/xsave.h
>> @@ -9,6 +9,8 @@
>>  #define XSTATE_FP	0x1
>>  #define XSTATE_SSE	0x2
>>  #define XSTATE_YMM	0x4
>> +#define XSTATE_BNDREGS	0x8
>> +#define XSTATE_BNDCSR	0x10
>>  
>>  #define XSTATE_FPSSE	(XSTATE_FP | XSTATE_SSE)
>>  
>> @@ -20,10 +22,12 @@
>>  #define XSAVE_YMM_SIZE	    256
>>  #define XSAVE_YMM_OFFSET    (XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET)
>>  
>> +#define XSTATE_FLEXIBLE (XSTATE_FP | XSTATE_SSE | XSTATE_YMM)
> 
> What's the use of that macro if it is used only once?

Documentation seems good enough.  Explicitly separating out the features
which MUST be eagerly saved seems like a good thing.

>> +#define XSTATE_EAGER	(XSTATE_BNDREGS | XSTATE_BNDCSR)
>>  /*
>>   * These are the features that the OS can handle currently.
>>   */
>> -#define XCNTXT_MASK	(XSTATE_FP | XSTATE_SSE | XSTATE_YMM)
>> +#define XCNTXT_MASK	(XSTATE_FLEXIBLE | XSTATE_EAGER)
>>  

	-hpa


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