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[2001:1c00:c14:2800:ec23:a060:24d5:2453]) by smtp.gmail.com with ESMTPSA id x5sm1967822ejc.53.2019.10.07.12.36.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Oct 2019 12:36:26 -0700 (PDT) Subject: Re: [PATCH v2 5.4 regression fix] x86/boot: Provide memzero_explicit To: Arvind Sankar , Ingo Molnar Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , Herbert Xu , Ard Biesheuvel , linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Stephan Mueller , linux-s390@vger.kernel.org References: <20191007134724.4019-1-hdegoede@redhat.com> <20191007140022.GA29008@gmail.com> <1dc3c53d-785e-f9a4-1b4c-3374c94ae0a7@redhat.com> <20191007142230.GA117630@gmail.com> <2982b666-e310-afb7-40eb-e536ce95e23d@redhat.com> <20191007144600.GB59713@gmail.com> <20191007152049.GA384920@rani.riverdale.lan> <20191007154007.GA96929@gmail.com> <20191007184237.GB13589@rani.riverdale.lan> From: Hans de Goede Message-ID: <1d17349e-98ab-b582-6981-b484b0e970b6@redhat.com> Date: Mon, 7 Oct 2019 21:36:25 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191007184237.GB13589@rani.riverdale.lan> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-crypto-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org Hi, On 07-10-2019 20:42, Arvind Sankar wrote: > On Mon, Oct 07, 2019 at 05:40:07PM +0200, Ingo Molnar wrote: >> >> * Arvind Sankar wrote: >> >>> With the barrier in there, is there any reason to *not* inline the >>> function? barrier_data() is an asm statement that tells the compiler >>> that the asm uses the memory that was set to zero, thus preventing it >>> from removing the memset even if nothing else uses that memory later. A >>> more detailed comment is there in compiler-gcc.h. I can't see why it >>> wouldn't work even if it were inlined. >>> >>> If the function can indeed be inlined, we could just make the common >>> implementation a macro and avoid duplicating it? As mentioned in another >>> mail, we otherwise will likely need another duplicate implementation for >>> arch/s390/purgatory as well. >> >> I suspect macro would be justified in this case. Mind sending a v3 patch >> to demonstrate how it would all look like? >> >> I'll zap v2 if the macro solution looks better. >> >> Thanks, >> >> Ingo > > Patch attached to turn memzero_explicit into inline function. Hehe, I had prepared and have just tested the exact same patch (only the commit msg was different). I've just booted a kernel build with that patch and that works fine (as expected). So your patch is: Reviewed-by: Hans de Goede Tested-by: Hans de Goede Since this is a bit of a core change though, I think it is best if you send it to the linux-kernel list (with my tags from above added) as is normally done for kernel patches. Then others, who may not be following this thread, will get a chance to give feedback on it. Regards, Hans