linux-kernel - Re: [PATCH] x86/sev: Don't use cc_platform

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Message-ID: <10bc452f-3564-e41b-836d-e135a8f4260d@intel.com>
Date:   Wed, 24 Aug 2022 11:43:10 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Asish Kalra <ashish.kalra@....com>,
        Michael Roth <michael.roth@....com>,
        Joerg Roedel <jroedel@...e.de>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH] x86/sev: Don't use cc_platform_has() for early SEV-SNP
 calls

On 8/23/22 14:55, Tom Lendacky wrote:
> When running identity mapped and depending on the kernel configuration,
> it is possible that cc_platform_has() can have compiler generated code
> that uses jump tables. This causes a boot failure because the jump table
> uses un-mapped kernel virtual addresses, not identity mapped addresses.
> This has been seen with CONFIG_RETPOLINE=n.

So, we don't have *ANY* control over where the compiler uses jump
tables.  The kernel just happened to add some code that uses them, fell
over, and this adds a hack to get booting again.

Isn't this a bigger problem?