linux-kernel - Re: [PATCH 12/70] x86/boot/compressed/64: Add IDT Infrastructure

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Date:   Mon, 6 Apr 2020 22:21:27 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 12/70] x86/boot/compressed/64: Add IDT Infrastructure

On Thu, Mar 19, 2020 at 10:13:09AM +0100, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> Add code needed to setup an IDT in the early pre-decompression
> boot-code. The IDT is loaded first in startup_64, which is after
> EfiExitBootServices() has been called, and later reloaded when the
> kernel image has been relocated to the end of the decompression area.
> 
> This allows to setup different IDT handlers before and after the
> relocation.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index 1f1f6c8139b3..d27a9ce1bcb0 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -465,6 +470,16 @@ SYM_FUNC_END_ALIAS(efi_stub_entry)
>  	.text
>  SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
>  
> +/*
> + * Reload GDT after relocation - The GDT at the non-relocated position
> + * might be overwritten soon by the in-place decompression, so reload
> + * GDT at the relocated address. The GDT is referenced by exception
> + * handling and needs to be set up correctly.
> + */
> +	leaq	gdt(%rip), %rax
> +	movq	%rax, gdt64+2(%rip)
> +	lgdt	gdt64(%rip)
> +
>  /*
>   * Clear BSS (stack is currently empty)
>   */

Note that this is now done in mainline as of commit c98a76eabbb6e, just
prior to jumping to .Lrelocated, so this can be dropped on the next
rebase.

Thanks.