linux-kernel - Re: [PATCH] x86: Don't use NOPL on 32-bit cpu's because not all systems support it.

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Date:	Tue, 16 Sep 2008 13:48:23 -0400
From:	David Sanders <linux@...dersweb.net>
To:	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:	the arch/x86 maintainers <x86@...nel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] x86: Don't use NOPL on 32-bit cpu's because not all systems support it.

On Tuesday 16 September 2008 12:32, H. Peter Anvin wrote:
> Oh good grief.
>
> VPC is apparently so broken that these instructions work *some* of the
> time, which may include the first time, but not later.  That is an
> impressive level of cockup.
>
> Given that, we should either just rip this code out, or detect VPC
> (how?).  The latter option can be done post-.27, of course; if so, we
> should just force the bit off for now rather than doing it in the
> alternatives code.  The only reason for doing the latter at all would be
> to mitigate the overhead of paravirt_ops and other dynamic patch sites.
>
> It would also be the least impact for .27, I believe.

I think you still want the nopl enabled for 64-bits.

This is how I detect virtual pc.  I based it on a google search.  Microsoft 
itself provides no info:

#include <stdio.h>
#include <signal.h>
#include <stdlib.h>

void except(int e)
{
	printf("Not in Virtual PC\n");
	exit(1);
}

int main()
{
	signal(SIGILL, except);
	asm("\n"
		"mov $0x01, %eax\n" /* function number */
		".byte 0x0f, 0x3f, 0x07, 0x0b\n" /* call VPC */
	   );
	printf("Inside Virtual PC\n");
	return 0;
}


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