linux-kernel - Re: [PATCH v2 1/1] x86/fred: Fix init_task thread stack pointer initialization

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Date: Wed, 6 Mar 2024 10:28:25 -0800
From: Xin Li <xin@...or.com>
To: linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        jgross@...e.com, boris.ostrovsky@...cle.com, arnd@...db.de,
        andrew.cooper3@...rix.com, brgerst@...il.com
Subject: Re: [PATCH v2 1/1] x86/fred: Fix init_task thread stack pointer
 initialization

On 3/4/2024 12:33 AM, Xin Li (Intel) wrote:
> As TOP_OF_KERNEL_STACK_PADDING is defined as 0 on x86_64, no one noticed
> it's missing in the calculation of the .sp field in INIT_THREAD until it
> is defined to 16 with CONFIG_X86_FRED=y.
> 
> Subtract TOP_OF_KERNEL_STACK_PADDING from the .sp field of INIT_THREAD.
> 
> Fixes: 65c9cc9e2c14 ("x86/fred: Reserve space for the FRED stack frame")
> Fixes: 3adee777ad0d ("x86/smpboot: Remove initial_stack on 64-bit")
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202402262159.183c2a37-lkp@intel.com
> Signed-off-by: Xin Li (Intel) <xin@...or.com>
> ---

Should this fix, if it looks good, be included for the coming merge
window?

Thanks!
     Xin

> 
> Change Since v1:
> * Apply offset TOP_OF_KERNEL_STACK_PADDING to all uses of __end_init_task
>    (Brian Gerst).
> ---
>   arch/x86/include/asm/processor.h | 6 ++++--
>   arch/x86/kernel/head_64.S        | 3 ++-
>   arch/x86/xen/xen-head.S          | 2 +-
>   3 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 26620d7642a9..17fe81998ce4 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -664,8 +664,10 @@ static __always_inline void prefetchw(const void *x)
>   #else
>   extern unsigned long __end_init_task[];
>   
> -#define INIT_THREAD {							    \
> -	.sp	= (unsigned long)&__end_init_task - sizeof(struct pt_regs), \
> +#define INIT_THREAD {							\
> +	.sp	= (unsigned long)&__end_init_task -			\
> +		  TOP_OF_KERNEL_STACK_PADDING -				\
> +		  sizeof(struct pt_regs),				\
>   }
>   
>   extern unsigned long KSTK_ESP(struct task_struct *task);
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index d4918d03efb4..c38e43589046 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -26,6 +26,7 @@
>   #include <asm/apicdef.h>
>   #include <asm/fixmap.h>
>   #include <asm/smp.h>
> +#include <asm/thread_info.h>
>   
>   /*
>    * We are not able to switch in one step to the final KERNEL ADDRESS SPACE
> @@ -66,7 +67,7 @@ SYM_CODE_START_NOALIGN(startup_64)
>   	mov	%rsi, %r15
>   
>   	/* Set up the stack for verify_cpu() */
> -	leaq	(__end_init_task - PTREGS_SIZE)(%rip), %rsp
> +	leaq	(__end_init_task - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE)(%rip), %rsp
>   
>   	leaq	_text(%rip), %rdi
>   
> diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
> index a0ea285878db..04101b984f24 100644
> --- a/arch/x86/xen/xen-head.S
> +++ b/arch/x86/xen/xen-head.S
> @@ -49,7 +49,7 @@ SYM_CODE_START(startup_xen)
>   	ANNOTATE_NOENDBR
>   	cld
>   
> -	leaq	(__end_init_task - PTREGS_SIZE)(%rip), %rsp
> +	leaq	(__end_init_task - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE)(%rip), %rsp
>   
>   	/* Set up %gs.
>   	 *
> 
> base-commit: e13841907b8fda0ae0ce1ec03684665f578416a8