linux-kernel - Re: [PATCH] x86, microcode: Remove unnecessary paravirt

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Message-ID: <CAHp75VebVT0U3fZNKeV1BWhHg-QXP3Lpk2T5=-HkrQt2V4_otA@mail.gmail.com>
Date:	Fri, 19 Feb 2016 12:06:33 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	david.vrabel@...rix.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] x86, microcode: Remove unnecessary paravirt_enabled check

On Thu, Feb 11, 2016 at 5:13 PM, Boris Ostrovsky
<boris.ostrovsky@...cle.com> wrote:
> Commit a18a0f6850d4 ("x86, microcode: Don't initialize microcode code on
> paravirt") added a paravirt test in microcode_init(), primarily to avoid
> making mc_bp_resume()->load_ucode_ap()->check_loader_disabled_ap() calls
> On 32-bit kernels this callchain ends up using __pa_nodebug() macro
> which is invalid for Xen PV guests.
>
> A subsequent commit, fbae4ba8c4a3 ("x86, microcode: Reload microcode on
> resume"), eliminated this callchain thus making a18a0f6850d4
> unnecessary.

Sorry for being too late, but this commit breaks 32-bit kernel on
Intel Medfield.
Reverting the only commit from today's linux-next helps.

Put me in Cc list to pursue testing whatever you come with.

> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
>  arch/x86/kernel/cpu/microcode/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index cea8552..ac360bf 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -623,7 +623,7 @@ int __init microcode_init(void)
>         struct cpuinfo_x86 *c = &boot_cpu_data;
>         int error;
>
> -       if (paravirt_enabled() || dis_ucode_ldr)
> +       if (dis_ucode_ldr)
>                 return -EINVAL;
>
>         if (c->x86_vendor == X86_VENDOR_INTEL)
> --
> 2.1.0
>



-- 
With Best Regards,
Andy Shevchenko