linux-kernel - Re: system locks up with CONFIG

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Date:   Wed, 16 Mar 2022 23:02:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Jamie Heilman <jamie@...ible.transient.net>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org
Subject: Re: system locks up with CONFIG_SLS=Y; 5.17.0-rc

On Wed, Mar 16, 2022 at 10:23:37PM +0100, Borislav Petkov wrote:
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index f667bd8df533..e88ce4171c4a 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -430,8 +430,11 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
>  	FOP_END
>  
>  /* Special case for SETcc - 1 instruction per cc */
> +
> +#define SETCC_ALIGN 8

I'd suggest writing that like:

	#define SETCC_ALIGN	(4 * (1 + IS_ENABLED(CONFIG_SLS)))

That way people can enjoy smaller text when they don't do the whole SLS
thing.... Also, it appears to me I added an ENDBR to this in
tip/x86/core, well, that needs fixing too. Tomorrow tho.

> +
>  #define FOP_SETCC(op) \
> -	".align 4 \n\t" \
> +	".align " __stringify(SETCC_ALIGN) " \n\t" \
>  	".type " #op ", @function \n\t" \
>  	#op ": \n\t" \
>  	ASM_ENDBR \
> @@ -1049,7 +1052,7 @@ static int em_bsr_c(struct x86_emulate_ctxt *ctxt)
>  static __always_inline u8 test_cc(unsigned int condition, unsigned long flags)
>  {
>  	u8 rc;
> -	void (*fop)(void) = (void *)em_setcc + 4 * (condition & 0xf);
> +	void (*fop)(void) = (void *)em_setcc + SETCC_ALIGN * (condition & 0xf);
>  
>  	flags = (flags & EFLAGS_MASK) | X86_EFLAGS_IF;
>  	asm("push %[flags]; popf; " CALL_NOSPEC
> -- 
> 2.29.2
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette