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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id s12sm3218300edu.28.2021.01.28.07.07.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Jan 2021 07:07:34 -0800 (PST) Subject: Re: [PATCH v2 05/14] KVM: x86: Override reported SME/SEV feature flags with host mask To: Sean Christopherson , Dave Hansen , Andy Lutomirski , Peter Zijlstra Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Borislav Petkov , Tom Lendacky , Brijesh Singh References: <20210114003708.3798992-1-seanjc@google.com> <20210114003708.3798992-6-seanjc@google.com> From: Paolo Bonzini Message-ID: <74642db3-14dc-4e13-3130-dc8abe1a2b6e@redhat.com> Date: Thu, 28 Jan 2021 16:07:31 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210114003708.3798992-6-seanjc@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14/01/21 01:36, Sean Christopherson wrote: > Add a reverse-CPUID entry for the memory encryption word, 0x8000001F.EAX, > and use it to override the supported CPUID flags reported to userspace. > Masking the reported CPUID flags avoids over-reporting KVM support, e.g. > without the mask a SEV-SNP capable CPU may incorrectly advertise SNP > support to userspace. > > Cc: Brijesh Singh > Cc: Tom Lendacky > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/cpuid.c | 2 ++ > arch/x86/kvm/cpuid.h | 1 + > 2 files changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 13036cf0b912..b7618cdd06b5 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -855,6 +855,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) > case 0x8000001F: > if (!boot_cpu_has(X86_FEATURE_SEV)) > entry->eax = entry->ebx = entry->ecx = entry->edx = 0; > + else > + cpuid_entry_override(entry, CPUID_8000_001F_EAX); > break; > /*Add support for Centaur's CPUID instruction*/ > case 0xC0000000: > diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h > index dc921d76e42e..8b6fc9bde248 100644 > --- a/arch/x86/kvm/cpuid.h > +++ b/arch/x86/kvm/cpuid.h > @@ -63,6 +63,7 @@ static const struct cpuid_reg reverse_cpuid[] = { > [CPUID_8000_0007_EBX] = {0x80000007, 0, CPUID_EBX}, > [CPUID_7_EDX] = { 7, 0, CPUID_EDX}, > [CPUID_7_1_EAX] = { 7, 1, CPUID_EAX}, > + [CPUID_8000_001F_EAX] = {0x8000001f, 1, CPUID_EAX}, > }; > > /* > I don't understand, wouldn't this also need a kvm_cpu_cap_mask call somewhere else? As it is, it doesn't do anything. Paolo