linux-kernel - Re: [PATCH 11/16] turn priviled operation into a macro in head

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Date:	Wed, 31 Oct 2007 21:50:50 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Glauber de Oliveira Costa <gcosta@...hat.com>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	rusty@...tcorp.com.au, ak@...e.de, mingo@...e.hu,
	chrisw@...s-sol.org, avi@...ranet.com, anthony@...emonkey.ws,
	virtualization@...ts.linux-foundation.org, lguest@...abs.org,
	kvm-devel@...ts.sourceforge.net, zach@...are.com,
	tglx@...utronix.de, jun.nakajima@...el.com, glommer@...il.com,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 11/16] turn priviled operation into a macro in head_64.S

Glauber de Oliveira Costa wrote:
> under paravirt, read cr2 cannot be issued directly anymore.
> So wrap it in a macro, defined to the operation itself in case
> paravirt is off, but to something else if we have paravirt
> in the game
>   

Is this actually needed?  It's only used in the early fault handler in
head_64.S.  Will we be taking that path in the paravirt case?  If so,
should we disable the fault handler altogether, since the hypervisor can
probably provide better diagnositcs.

    J
> Signed-off-by: Glauber de Oliveira Costa <gcosta@...hat.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> Acked-by: Jeremy Fitzhardinge <jeremy@...source.com>
> ---
>  arch/x86/kernel/head_64.S |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index b6167fe..c31b1c9 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -19,6 +19,13 @@
>  #include <asm/msr.h>
>  #include <asm/cache.h>
>  
> +#ifdef CONFIG_PARAVIRT
> +#include <asm/asm-offsets.h>
> +#include <asm/paravirt.h>
> +#else
> +#define GET_CR2_INTO_RCX movq %cr2, %rcx
> +#endif
> +
>  /* we are not able to switch in one step to the final KERNEL ADRESS SPACE
>   * because we need identity-mapped pages.
>   *
> @@ -267,7 +274,7 @@ ENTRY(early_idt_handler)
>  	xorl %eax,%eax
>  	movq 8(%rsp),%rsi	# get rip
>  	movq (%rsp),%rdx
> -	movq %cr2,%rcx
> +	GET_CR2_INTO_RCX
>  	leaq early_idt_msg(%rip),%rdi
>  	call early_printk
>  	cmpl $2,early_recursion_flag(%rip)
>   

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