linux-kernel - Re: [PATCHv3, RESEND] x86/trampoline: Bypass compat mode in trampoline

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Date: Thu, 25 Jan 2024 06:50:07 -0800
From: Andi Kleen <ak@...ux.intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: 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>, linux-kernel@...r.kernel.org,
	Kai Huang <kai.huang@...el.com>,
	Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCHv3, RESEND] x86/trampoline: Bypass compat mode in
 trampoline_start64() if not needed

> I think it is cleaner to switch to IRET here. Does this work for you?
> 
> diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
> index 608f108cba7d..14d9c7daf90f 100644
> --- a/arch/x86/realmode/rm/trampoline_64.S
> +++ b/arch/x86/realmode/rm/trampoline_64.S
> @@ -243,7 +243,9 @@ SYM_CODE_START(trampoline_start64)
>  	movl	$pa_trampoline_pgd, %eax
>  	movq	%rax, %cr3
>  
> -	jmpq	*tr_start(%rip)
> +	pushq	$__KERNEL_CS
> +	pushq	tr_start(%rip)
> +	lretq

Looks good. Thanks.

-Andi