Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 4 Feb 2022 19:00:49 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Tom Lendacky <thomas.lendacky@amd.com>
Cc:     "Limonciello, Mario" <mario.limonciello@amd.com>,
        Martin Fernandez <martin.fernandez@eclypsium.com>,
        linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org,
        platform-driver-x86@vger.kernel.org, linux-mm@kvack.org,
        tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com,
        x86@kernel.org, hpa@zytor.com, ardb@kernel.org,
        dvhart@infradead.org, andy@infradead.org,
        gregkh@linuxfoundation.org, rafael@kernel.org, rppt@kernel.org,
        akpm@linux-foundation.org, daniel.gutson@eclypsium.com,
        hughsient@gmail.com, alex.bazhaniuk@eclypsium.com,
        alison.schofield@intel.com, keescook@chromium.org
Subject: Re: [PATCH v6 6/6] drivers/node: Show in sysfs node's crypto
 capabilities
Message-ID: <Yf1p0ZjPf9Qaqwtg@zn.tnic>
References: <20220203164328.203629-1-martin.fernandez@eclypsium.com>
 <20220203164328.203629-7-martin.fernandez@eclypsium.com>
 <67d2711b-200c-0894-4ff7-beb3eb304399@amd.com>
 <CAKgze5YM2+BRjj2nvb+_dnuCg5WtWvQ6FQyNYJ1c8G6Orn=aQw@mail.gmail.com>
 <5c5ffe29-d3d3-2955-cf78-ad275110f012@amd.com>
 <ec9e29a4-0d2b-1423-d92e-6f025b56f8cc@amd.com>
 <Yf1UO6jF91o9k4jB@zn.tnic>
 <5ee34cad-8daf-6282-f2ed-cbc92a89d013@amd.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <5ee34cad-8daf-6282-f2ed-cbc92a89d013@amd.com>
Precedence: bulk

On Fri, Feb 04, 2022 at 11:12:04AM -0600, Tom Lendacky wrote:
> https://elixir.bootlin.com/linux/latest/source/arch/x86/kernel/process.c#L761

For those who won't open a browser just to see what he means :), that's
this snippet:

void stop_this_cpu(void *dummy):
	/*
	 * Use wbinvd on processors that support SME. This provides support
	 * for performing a successful kexec when going from SME inactive
	 * to SME active (or vice-versa). The cache must be cleared so that
	 * if there are entries with the same physical address, both with and
	 * without the encryption bit, they don't race each other when flushed
	 * and potentially end up with the wrong entry being committed to
	 * memory.
	 */
	if (boot_cpu_has(X86_FEATURE_SME))
		native_wbinvd();


Well, we do clear our *representation* of CPUID flags for other features
- see output of

$ git grep -E "(setup_)?clear_cpu_cap"

for examples. We do that for SME even: early_detect_mem_encrypt().

Which means, since this needs to be "processors that support SME", this
line should change to:

	/* ... test the CPUID bit directly because the machine might've cleared
	 * X86_FEATURE_SME due to cmdline options.
	 */
	if (cpuid_eax(0x8000001f) & BIT(0))
		native_wbinvd();

I'd say...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette