linux-kernel - Re: [PATCH repost] x86/boot: Add a message about ignored early NMIs

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Date: Fri, 12 Jan 2024 15:06:16 +0300
From: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To: NOMURA JUNICHI(野村　淳一) <junichi.nomura@....com>
Cc: "mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"bp@...en8.de" <bp@...en8.de>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
	"ardb@...nel.org" <ardb@...nel.org>,
	"david@...hat.com" <david@...hat.com>,
	"nikunj@....com" <nikunj@....com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>,
	"debarbos@...hat.com" <debarbos@...hat.com>,
	"jlelli@...hat.com" <jlelli@...hat.com>,
	"lgoncalv@...hat.com" <lgoncalv@...hat.com>,
	"dzickus@...hat.com" <dzickus@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH repost] x86/boot: Add a message about ignored early NMIs

On Fri, Jan 12, 2024 at 11:13:53AM +0000, NOMURA JUNICHI(野村 淳一) wrote:
> Commit 78a509fba9c9 ("x86/boot: Ignore NMIs during very early boot") added
> empty handler in early boot stage to avoid boot failure by spurious NMIs.
> 
> Add a diagnostic message in case we need to know whether early NMIs have
> occurred and/or what happened to them.
> 
> Signed-off-by: Jun'ichi Nomura <junichi.nomura@....com>
> Suggested-by: Borislav Petkov <bp@...en8.de>
> Suggested-by: H. Peter Anvin <hpa@...or.com>
> Link: https://lore.kernel.org/lkml/20231130103339.GCZWhlA196uRklTMNF@fat_crate.local/
> 
> diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
> --- a/arch/x86/boot/compressed/ident_map_64.c
> +++ b/arch/x86/boot/compressed/ident_map_64.c
> @@ -387,7 +387,10 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
>  	kernel_add_identity_map(address, end);
>  }
>  
> +extern int spurious_nmi_count;
> +

It has to be in a header file.

>  void do_boot_nmi_trap(struct pt_regs *regs, unsigned long error_code)
>  {
>  	/* Empty handler to ignore NMI during early boot */
> +	spurious_nmi_count++;
>  }
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -357,6 +357,8 @@ unsigned long decompress_kernel(unsigned char *outbuf, unsigned long virt_addr,
>  	return entry;
>  }
>  
> +int spurious_nmi_count;
> +

It is not a right place to define a variable. Do it next to rest of
variables at the beginning of the file.
>  /*
>   * The compressed kernel image (ZO), has been moved so that its position
>   * is against the end of the buffer used to hold the uncompressed kernel
> @@ -493,6 +495,12 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
>  	/* Disable exception handling before booting the kernel */
>  	cleanup_exception_handling();
>  
> +	if (spurious_nmi_count) {
> +		error_putstr("Spurious early NMI ignored. Number of NMIs: 0x");
> +		error_puthex(spurious_nmi_count);
> +		error_putstr("\n");
> +	}
> +
>  	return output + entry_offset;
>  }
>  

-- 
  Kiryl Shutsemau / Kirill A. Shutemov