linux-kernel - Re: [PATCH v4] x86/cpu: clear SME feature flag when not in use

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Date:   Wed, 16 Feb 2022 09:05:07 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Mario Limonciello <mario.limonciello@....com>,
        Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>, hughsient@...il.com,
        Martin Fernandez <martin.fernandez@...ypsium.com>,
        linux-kernel@...r.kernel.org, Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v4] x86/cpu: clear SME feature flag when not in use

On 2/15/22 21:44, Mario Limonciello wrote:
> Currently the SME CPU feature flag is reflective of whether the CPU
> supports the feature but not whether is has been activated by the
> kernel.
> 
> Change this around to clear the SME feature flag if the kernel is not
> using it so userspace can determine if it is available and in use
> from `/proc/cpuinfo`.
> 
> As the feature flag is cleared on systems where SME isn't active use
> CPUID 0x8000001f to confirm SME availability before calling
> `native_wbinvd`.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>

Acked-by: Tom Lendacky <thomas.lendacky@....com>

> ---