From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH 1/1 v2] KVM: MMU: Optimize guest page table walk
Date: Tue, 26 Apr 2011 11:21:10 +0300
Message-ID: <4DB68076.8090902@redhat.com>
References: <20110422003222.9d08aee3.takuya.yoshikawa@gmail.com> <20110422003444.5b3a876a.takuya.yoshikawa@gmail.com> <4DB52B1B.5080407@web.de> <4DB6775F.9050207@redhat.com> <4DB67823.4010304@web.de>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Cc: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>, mtosatti@redhat.com,
	kvm@vger.kernel.org, yoshikawa.takuya@oss.ntt.co.jp,
	xiaoguangrong@cn.fujitsu.com, Joerg.Roedel@amd.com
To: Jan Kiszka <jan.kiszka@web.de>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:1027 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750941Ab1DZIVZ (ORCPT <rfc822;kvm@vger.kernel.org>);
	Tue, 26 Apr 2011 04:21:25 -0400
In-Reply-To: <4DB67823.4010304@web.de>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On 04/26/2011 10:45 AM, Jan Kiszka wrote:
> On 2011-04-26 09:42, Avi Kivity wrote:
> >  On 04/25/2011 11:04 AM, Jan Kiszka wrote:
> >>  >   +
> >>  >   +        ptep_user = (pt_element_t __user *)((void *)host_addr +
> >>  offset);
> >>  >   +        if (get_user(pte, ptep_user)) {
> >>                       ^^^^^^^^^^^^
> >>  This doesn't work for x86-32: pte is 64 bit, but get_user is only
> >>  defined up to 32 bit on that platform.
> >>
> >
> >  I actually considered this, and saw:
> >
> >  #ifdef CONFIG_X86_32
> >  #define __get_user_8(__ret_gu, __val_gu, ptr)                \
> >          __get_user_x(X, __ret_gu, __val_gu, ptr)
> >  #else
> >  #define __get_user_8(__ret_gu, __val_gu, ptr)                \
> >          __get_user_x(8, __ret_gu, __val_gu, ptr)
> >  #endif
> >
> >  #define get_user(x, ptr)                        \
> >  ({                                    \
> >      int __ret_gu;                            \
> >      unsigned long __val_gu;                        \
> >      __chk_user_ptr(ptr);                        \
> >      might_fault();                            \
> >      switch (sizeof(*(ptr))) {                    \
> >
> >  ...
> >
> >      case 8:                                \
> >          __get_user_8(__ret_gu, __val_gu, ptr);            \
> >          break;                            \
> >
> >  ...
> >
> >      }                                \
> >      (x) = (__typeof__(*(ptr)))__val_gu;                \
> >      __ret_gu;                            \
> >  })
> >
> >  so it should work.  How does it fail?
>
> On x86-32, the above macro resolves to __get_user_X, an undefined symbol.
>

Tricky stuff.

-- 
error compiling committee.c: too many arguments to function