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From:   Ricardo =?utf-8?Q?Ca=C3=B1uelo?= <ricardo.canuelo@collabora.com>
To:     Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc:     Borislav Petkov <bp@alien8.de>, linux-kernel@vger.kernel.org,
        Thadeu Lima de Souza Cascardo <cascardo@canonical.com>,
        Mark Gross <mgross@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Johansen <john.johansen@canonical.com>,
        Steve Beattie <sbeattie@ubuntu.com>, kernel@collabora.com
Subject: Re: [PATCH v2] x86/speculation/srbds: do not try to turn mitigation off when not supported
References: <20220330082026.1549073-1-ricardo.canuelo@collabora.com> <YkS3OKLS1Cixs9up@zn.tnic> <87o81mzhoh.fsf@rcn-XPS-13-9305.i-did-not-set--mail-host-address--so-tickle-me> <20220331084536.y4sl7qcfzltsnnew@guptapa-desk>
In-reply-to: <20220331084536.y4sl7qcfzltsnnew@guptapa-desk>
Date:   Thu, 31 Mar 2022 15:18:42 +0200
Message-ID: <87lewqz2dp.fsf@rcn-XPS-13-9305.i-did-not-set--mail-host-address--so-tickle-me>
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Pawan Gupta <pawan.kumar.gupta@linux.intel.com> writes:

Hi Pawan,

>   void update_srbds_msr(void)
>   {
>   	u64 mcu_ctrl;
>   
> -	if (!boot_cpu_has_bug(X86_BUG_SRBDS))
> -		return;
> -
> -	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
> -		return;
> -
> -	if (srbds_mitigation == SRBDS_MITIGATION_UCODE_NEEDED)
> +	if (!boot_cpu_has_bug(X86_BUG_SRBDS) ||
> +	    !boot_cpu_has(X86_FEATURE_SRBDS_CTRL))
>   		return;

Just to clarify, this changes the behavior wrt the hypervisor case:
currently it just bails out of update_srbds_msr(), with your patch it'd
clear RNGDS_MITG_DIS from MSR_IA32_MCU_OPT_CTRL. Is that what you
intended?

Ricardo