linux-kernel - Re: [PATCH 1/4] x86/wakeup/sleep: Check whether the TSS GDT descriptor is empty before using it.

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Message-ID: <507F473D.1060700@zytor.com>
Date:	Wed, 17 Oct 2012 17:03:09 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	lenb@...nel.org, linux-acpi@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 1/4] x86/wakeup/sleep: Check whether the TSS GDT descriptor
 is empty before using it.

On 10/17/2012 06:49 AM, Konrad Rzeszutek Wilk wrote:
> We check the TSS descriptor before we try to dereference it.
> Also fix up the value to use the #defines.
>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>   arch/x86/power/cpu.c |    7 +++++--
>   1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
> index 218cdb1..c17370e 100644
> --- a/arch/x86/power/cpu.c
> +++ b/arch/x86/power/cpu.c
> @@ -133,7 +133,9 @@ static void fix_processor_context(void)
>   {
>   	int cpu = smp_processor_id();
>   	struct tss_struct *t = &per_cpu(init_tss, cpu);
> -
> +#ifdef CONFIG_X86_64
> +	struct desc_struct *desc = get_cpu_gdt_table(cpu);
> +#endif
>   	set_tss_desc(cpu, t);	/*
>   				 * This just modifies memory; should not be
>   				 * necessary. But... This is necessary, because
> @@ -142,7 +144,8 @@ static void fix_processor_context(void)
>   				 */
>
>   #ifdef CONFIG_X86_64
> -	get_cpu_gdt_table(cpu)[GDT_ENTRY_TSS].type = 9;
> +	if (!desc_empty(&desc[GDT_ENTRY_TSS]))
> +		desc[GDT_ENTRY_TSS].type = DESC_TSS;
>
>   	syscall_init();				/* This sets MSR_*STAR and related */
>   #endif
>

Why is this patch necessary?  Presumably there is something further down 
the line which depends on the TSS descriptor being empty, but if so, what?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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