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From:   Andi Kleen <ak@linux.intel.com>
To:     Joerg Roedel <joro@8bytes.org>
Cc:     x86@kernel.org, hpa@zytor.com, Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        Jiri Slaby <jslaby@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Juergen Gross <jgross@suse.com>,
        Kees Cook <keescook@chromium.org>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH 08/62] x86/boot/compressed/64: Add IDT Infrastructure
References: <20200211135256.24617-1-joro@8bytes.org>
        <20200211135256.24617-9-joro@8bytes.org>
Date:   Fri, 14 Feb 2020 11:40:36 -0800
In-Reply-To: <20200211135256.24617-9-joro@8bytes.org> (Joerg Roedel's message
        of "Tue, 11 Feb 2020 14:52:02 +0100")
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Joerg Roedel <joro@8bytes.org> writes:
> +	addq    $8, %rsp
> +
> +	/*
> +	 * Make sure we return to __KERNEL_CS - the CS selector on
> +	 * the IRET frame might still be from an old BIOS GDT
> +	 */
> +	movq	$__KERNEL_CS, 8(%rsp)

This doesn't make sense. Either it's running on the correct CS
before the exception or not. Likely there's some other problem
here that you patched over with this hack.

-Andi