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([2001:b07:6468:f312:63a7:c72e:ea0e:6045]) by smtp.gmail.com with ESMTPSA id gb2sm2413667ejc.52.2021.11.04.03.00.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Nov 2021 03:00:18 -0700 (PDT) Message-ID: <3f4bf34f-fdc2-37f7-c789-249f19b0653f@redhat.com> Date: Thu, 4 Nov 2021 11:00:15 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH] crypto: x86/aes-ni: fix AVX detection Content-Language: en-US To: Herbert Xu , Dave Hansen Cc: Maxim Levitsky , linux-kernel@vger.kernel.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "open list:CRYPTO API" , Dave Hansen , Thomas Gleixner , Borislav Petkov , Ingo Molnar , "David S. Miller" , "H. Peter Anvin" , Tim Chen References: <20211103124614.499580-1-mlevitsk@redhat.com> <622444d6-f98b-dae4-381e-192e5cb02621@intel.com> <20211103145231.GA4485@gondor.apana.org.au> From: Paolo Bonzini In-Reply-To: <20211103145231.GA4485@gondor.apana.org.au> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/3/21 15:52, Herbert Xu wrote: > On Wed, Nov 03, 2021 at 07:43:43AM -0700, Dave Hansen wrote: >> The kernel shouldn't crash in this case. We've got a software >> dependency which should disable AVX2 if AVX is off: > It's qemu, I thought it was a qemu bug but Paulo disagrees. I don't disagree that QEMU could do better in preventing nonsensical combinations; however, independent of that you shouldn't use AVX2 without factoring XCR0 in the decision. This is true no matter if userspace/kernel or even bare metal/virt. That does not have to be done directly with cpu_has_xfeatures as in Maxim's patch: if boot_cpu_has(AVX) returns false after xsave_cpuid_features has filtered it out, or if boot_cpu_has(AVX2) returns false after cpuid_deps has filtered it out, that's fine. I guess Maxim can look at the pointers that Dave provided and check if there's another bug somewhere in arch/x86/kernel. Paolo