linux-kernel - Re: Can't boot as Xen dom0 due to commit fe055896

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Date:   Thu, 15 Dec 2016 12:27:49 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Juergen Gross <jgross@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>
Subject: Re: Can't boot as Xen dom0 due to commit fe055896

On 12/15/2016 12:17 PM, Borislav Petkov wrote:
> On Thu, Dec 15, 2016 at 12:00:22PM -0500, Boris Ostrovsky wrote:
>> There is an error on AMD as well. We end up being called at
>> load_microcode_amd() with size=0 and crash soon after.
> Does that fix it?
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index dd47e60aabf5..e238119b5dff 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1202,6 +1202,7 @@ config X86_REBOOTFIXUPS
>  config MICROCODE
>  	bool "CPU microcode loading support"
>  	default y
> +	depends on !XEN
>  	depends on CPU_SUP_AMD || CPU_SUP_INTEL
>  	select FW_LOADER
>  	---help---


It will probably fix it but I don't think we want this: it's a
build-time solution. Most kernels have XEN on even though they are
booted bare-metal.

>
>> (As a side note, I think verify_and_add_patch() should return error
>> codes and not crnt_size, which may be a positive number. Which it was in
>> my case.)
> It does return negative values when there's some failure. 

I meant, for example:

        proc_fam = find_cpu_family_by_equiv_cpu(proc_id);
        if (!proc_fam) {
                pr_err("No patch family for equiv ID: 0x%04x\n", proc_id);
                return crnt_size;
        }

-boris

> It returns
> crnt_size which can be a positive number so that we can advance to the
> next patch in the blob.
>