linux-kernel - Re: [PATCH 1/4] x86-64: Allow emulated vsyscalls from user addresses

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Message-ID: <CAObL_7Fq9qHNgu6-+bhagp=_kVnKzx2Kb1BufR2=g6pGeNEPdQ@mail.gmail.com>
Date:	Tue, 9 Aug 2011 15:16:50 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	x86@...nel.org, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	lueckintel@...oo.com, kimwooyoung@...il.com,
	Ingo Molnar <mingo@...e.hu>, Borislav Petkov <bp@...en8.de>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH 1/4] x86-64: Allow emulated vsyscalls from user addresses

On Tue, Aug 9, 2011 at 2:59 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 08/09/2011 09:27 AM, Andy Lutomirski wrote:
>>   *
>>   *  Vectors   0 ...  31 : system traps and exceptions - hardcoded events
>> - *  Vectors  32 ... 127 : device interrupts
>> - *  Vector  128         : legacy int80 syscall interface
>> - *  Vector  204         : legacy x86_64 vsyscall emulation
>> - *  Vectors 129 ... INVALIDATE_TLB_VECTOR_START-1 except 204 : device interrupts
>> + *  Vectors  32 ... INVALIDATE_TLB_VECTOR_START-1 : device interrupts, except:
>> + *   Vectors 64 ... 66  : legacy x86_64 vsyscall emulation
>> + *   Vector  128        : legacy int80 syscall interface
>>   *  Vectors INVALIDATE_TLB_VECTOR_START ... 255 : special interrupts
>>   *
>
> Hi Andy,
>
> Was there a reason to not use the vectors in the 0x2X range?

My general lack of understanding of how all the numbers work, and the
fact that I was waiting for Suresh to answer.  I assumed that
/proc/interrupts showed numbers that corresponded to offsets from
FIRST_EXTERNAL_VECTOR, in which case the 0x2X range is no good.  I
think that's wrong and they start at 0x40 (maybe?).  This comment in
irq_vector.h doesn't help:

/*
 * Vectors 0x30-0x3f are used for ISA interrupts.
 *   round up to the next 16-vector boundary
 */
#define IRQ0_VECTOR                     ((FIRST_EXTERNAL_VECTOR + 16) & ~15)


If IRQ0_VECTOR is a legacy ISA interrupt, then it's 0x30.  So what's
with the rounding?  In any case, I don't actually know which vector
irq 18 uses, and I don't know how to dump that information out of
/proc or /sys.



In any case, I won't fix this unless you and/or the rest of the x86
maintainers tell me you prefer this patch to the one that adds a
vsyscall boot parameter.

--Andy
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