linux-kernel - Re: [PATCH 1/2] x86/fred: Always install system interrupt handler into IDT

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Date: Tue, 25 Jun 2024 02:19:20 -0700
From: Xin Li <xin@...or.com>
To: Hou Wenlong <houwenlong.hwl@...group.com>, linux-kernel@...r.kernel.org
Cc: Lai Jiangshan <jiangshan.ljs@...group.com>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Xin Li
 <xin3.li@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 1/2] x86/fred: Always install system interrupt handler
 into IDT

On 6/21/2024 6:12 AM, Hou Wenlong wrote:
> In sysvec_install(), the system interrupt handler is not installed into
> the IDT when the FRED feature is present, but FRED can be disabled
> in trap_init(). However, sysvec_install() can be used
> before trap_init(), e.g., the HYPERVISOR_CALLBACK_VECTOR handler is
> registered in kvm_guest_init(), which is called by setup_arch() before
> trap_init(). If FRED is disabled later, then the spurious_interrupt()
> handler will be used due to the handler not being installed into the
> IDT. Therefore, always install system interrupt handler into IDT.
> 
> Fixes: 3810da12710a ("x86/fred: Add a fred= cmdline param")
> Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> ---
>   arch/x86/include/asm/idtentry.h | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
> index d4f24499b256..daee9f7765bc 100644
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -470,8 +470,7 @@ static inline void fred_install_sysvec(unsigned int vector, const idtentry_t fun
>   #define sysvec_install(vector, function) {				\
>   	if (cpu_feature_enabled(X86_FEATURE_FRED))			\
>   		fred_install_sysvec(vector, function);			\
> -	else								\
> -		idt_install_sysvec(vector, asm_##function);		\

empty line, it improves readability.

And please put a comment here to explain why this is unconditionally
done for IDT.

> +	idt_install_sysvec(vector, asm_##function);			\
>   }
>   
>   #else /* !__ASSEMBLY__ */

Thanks!
     Xin